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Effect of herbicide clomazone on photosynthetic processes in primary barley (Hordeum vulgare L.) leaves
Abstract
The effect of pre-emergently applied herbicide clomazone on the photosynthetic apparatus of primary barley leaves (Hordeum vulgare L.) was studied. Clomazone application caused a reduction in chlorophyll (a + b) and carotenoid levels that was accompanied by a decline in the content of light harvesting complexes as judged from the increasing chlorophyll a/b ratio. The pigment reduction also resulted in changes in 77 K chlorophyll fluorescence emission spectra indicating lower chlorophyll (Chl) fluorescence reabsorption and absence of the long-wavelength emission forms of photosystem I. The maximal photochemical yield of photosystem II (PSII) and the reoxidation kinetics of the primary quinone acceptor QA- were not significantly influenced by clomazone. A higher initial slope of Chl fluorescence rise in the Chl fluorescence induction kinetic indicated an increased delivery of excitations to PSII. Simultaneously, analysis of the Chl fluorescence quenching revealed that clomazone reduced function of the electron transport chain behind PSII. The decrease in the saturation rates of CO2 assimilation paralleled the decrease of the Chl content and has been suggested to be caused by a suppressed number of the electron transport chains in the thylakoid membranes or by their decreased functionality. The obtained results are discussed in view of physiological similarity of the clomazone effect with changes of photosynthetic apparatus during photoadaptation.
... It was possible to observe the typical effects of clomazone in S. viridis leaves, characterized by complete depigmentation that emerged after the herbicide had been applied (Fig. 1E). This is associated with the action of clomazone as an inhibitor of carotenoids biosynthesis followed by degradation of chlorophyll caused by photo-inhibition (Ka na et al., 2004). Carotenoids are pigments involved in photosynthesis, photoprotection and membrane stabilization (Vítek et al., 2017;Biswal, 1995). ...
... This difference could be related to the increase of necrosis points over time, mainly due to the herbicide's direct contact on the S. viridis leaves. A similar reduction in the content of photosynthetic pigments as an effect of the clomazone application was observed in Hordeum vulgare L. (Ka na et al., 2004) and this preferential reduction of chlorophyll a overtime suggested degradation of the chlorophyll a-containing light-harvesting complexes (LHCs) in thylakoid membranes. Similar decreases were observed under higher concentrations of clomazone in plantlets leaves of tobacco (Darwish et al., 2014), in adult leaves of tobacco and tomato (Darwish et al., 2013;Scott et al., 1994), and in the adult leaves of barley (Ka na et al., 2004). ...
... A similar reduction in the content of photosynthetic pigments as an effect of the clomazone application was observed in Hordeum vulgare L. (Ka na et al., 2004) and this preferential reduction of chlorophyll a overtime suggested degradation of the chlorophyll a-containing light-harvesting complexes (LHCs) in thylakoid membranes. Similar decreases were observed under higher concentrations of clomazone in plantlets leaves of tobacco (Darwish et al., 2014), in adult leaves of tobacco and tomato (Darwish et al., 2013;Scott et al., 1994), and in the adult leaves of barley (Ka na et al., 2004). Here, therefore, after the pigment content of S. viridis in the young leaf blades was drastically affected by clomazone, the pigment pre-existing in older leaf blades may have suffered degradation by photo-inhibition. ...
Clomazone and saflufenacil are herbicides extensively used worldwide to weed control. We studied the effects of these two herbicides on morphoanatomical parameters of Setaria viridis. Plants were sprayed with four concentrations of each herbicide (clomazone: 500, 1000, 1500 and 2000 g of active ingredient (ai) ha−1 and saflufenacil: 49, 98, 147 and 196 g ai ha−1) besides control (without spraying) 20 days after transplantation. The experimental design was completely randomized with five replicates per treatment. Pigment content, visible injuries, morphological and ultrastructural changes were evaluated. No signs of tolerance to either of the tested herbicides were observed. Clomazone caused a decrease in photosynthetic pigment content over time, mostly in young leaves, leading to an “albino” like appearance. There was a reduction in the number of grana in the chloroplasts of mesophyll cells (MC) in necrotic areas. Saflufenacil reduced chlorophyll content, impairing energy absorption in the antenna complex. Injuries to foliar tissues, such as necrosis and depigmentation, were visible as early as 24 h after herbicide application. Bundle sheath chloroplasts (BSC) and MC were completely deformed. The data support the use of S. viridis as a model plant for studies on herbicide effects in C4 monocots.
... The development of herbicide symptoms in shoots is understood to reflect the amount and speed of herbicide absorbed by deep roots, and can thus be used as an indicator of root depth and root activity. Specifically, the herbicide chosen for our study, clomazone, blocks the synthesis of chlorophyll and other pigments and thus causes bleaching of the leaves, which can be readily observed (Kaňa et al. 2004;Corre-Hellou and Crozat 2005). The Herbicide technique relied on the bleaching effect of the active substance clomazone on photosystem II and the reduction of chlorophyll in leaves, while it is sensitive to low light intensity (Kaňa et al. 2004). ...
... Specifically, the herbicide chosen for our study, clomazone, blocks the synthesis of chlorophyll and other pigments and thus causes bleaching of the leaves, which can be readily observed (Kaňa et al. 2004;Corre-Hellou and Crozat 2005). The Herbicide technique relied on the bleaching effect of the active substance clomazone on photosystem II and the reduction of chlorophyll in leaves, while it is sensitive to low light intensity (Kaňa et al. 2004). ...
Selection for deep rooting is critical for the development of genotypes that are able to explore deep soil water and nutrients, particularly as agricultural resources become more limited. However, current root phenotyping techniques demand significant investments of time, money, and effort, and measurements on very young plants or plants grown under soilless culture. This study introduced four novel and simple techniques for fast evaluation of root depth in tube rhizotrons, which enable root observation around the transparent tube walls, and allow roots growing to natural size in semi-field conditions. The first and second innovations involve the introduction of ¹⁵N tracer and herbicide to the roots, which estimated root activity by measuring the responses of the shoots aboveground. The third involves placement of a cone deep in the rhizotron, to increase chances to observe more deep roots along the tube walls. The fourth involves measurement of roots that emerge from the rhizotron bottom. The reliability of these techniques were assessed in a series of five experiments during 2014 and 2015. These tests compared two pairs of genotypes that previous studies had shown to have mutually distinctive root traits: the spring wheat pair of ‘April bearded’ vs. ‘Dacke’; and the winter wheat pair of ‘Tabasco’ vs. ‘Genius’, with the first of each pair being the genotype known for deep rooting. Results showed that the new techniques were as good as or better than existing alternatives at accurately measuring root traits. In eight of the nine comparisons, the measurements were consistent with the expectations of root characteristics for these known genotypes. Importantly, the indirect root activity measures (herbicide and ¹⁵N) showed the same trend as the direct root observation techniques in all experiments, but higher ability to distinguish the genotypes and more promise for future upscaling for plant breeding.
... Some studies have indicated that nicosulfuron can reduce chlorophyll (Chl) contents and photosynthesis, thereby inhibiting plant growth (Saladin et al. 2003, Belgers et al. 2007, Bigot et al. 2007, Macedo et al. 2008, Hussain et al. 2010. Herbicide application damages the photosynthetic apparatus within the PSI and PSII, thus reducing the maximum photochemical efficiency of PSII (Fv/Fm), the photochemical quenching coefficient (q P ), and the ---quantum yield of PSII electron transport (Ф PSII ) (Kaňa et al. 2004, Tan et al. 2012, Hu et al. 2014, Debona et al. 2016. This is due to the excessive reactive oxygen species (ROS) which are produced by photosynthesis under the stress conditions. ...
... Herbicide-induced damage to crops can be evaluated by measuring agronomic traits and physiological indexes. Many herbicides are photosynthesis inhibitors, that operate by interfering with the electron transport rate, which is significantly reduced in the thylakoid membranes of chloroplasts from plants treated with clomazone (Kaňa et al. 2004). A similar effect occurs following atrazine treatment. ...
Nicosulfuron is a post-emergence herbicide used for weed control in fields of maize (Zea mays L.). We used a pair of nearly isogenic inbred lines, SN509-R (nicosulfuron-resistant) and SN509-S (nicosulfuron-sensitive), to study the effect of nicosulfuron on waxy maize seedling. After the nicosulfuron treatment, net photosynthetic rate, stomatal conductance, transpiration rate, leaf maximum photochemical efficiency of PSII, photochemical quenching of chlorophyll fluorescence, and the actual photochemical efficiency of PSII were significantly lower in SN509-S than those of SN509-R, contrary to intercellular CO2 concentration, stomatal limitation, and nonphotochemical quenching. Compared to SN509-R, antioxidant enzyme activities in SN509-S decreased significantly in response to the nicosulfuron treatment, while SN509-S exhibited an increased malondialdehyde content, which was associated with lower antioxidant enzyme activities. These results collectively suggest that the nicosulfuron-resistance mechanism was associated with photosynthetic rate, reactive oxygen species metabolism, and protective mechanisms.
... Methods based on chlorophyll a fluorescence (ChlF) were developed to detect photosystem II (PSII) inhibitors in the environment [9]. More recently, ChlF was employed in detecting activity of acetolactate synthase (ALS) inhibitors [10], carotenoid biosynthesis [11], and protoporphyrinogen oxidase (PPO) inhibitors [12]. ...
... Under short exposure to carotenoid biosynthesis inhibitors, the effect on the electron transport rate has been reported to be relatively low [12]. Longer exposure, however, led to a significant reduction in photosynthetic electron transport [11]. ...
... Our experiment shows that clomazone caused not only a reduction in chlorophyll and carotenoid levels but also a decline in the content of LHCII (Chl a/b ratio) in tobacco plantlets ( Table 2). A similar decrease was observed in the case of a higher concentration of clomazone in the adult leaves of tobacco and tomato [7,42], and the adult leaves of barley seedlings [43]. Due to the effect of clomazone in the reduction of the antenna pigments (LHCII), an excessive influx of the excitation ABS is transferred into the active reaction centre (RC) of the photosystem II according to Kaň a et al. [43]. ...
... A similar decrease was observed in the case of a higher concentration of clomazone in the adult leaves of tobacco and tomato [7,42], and the adult leaves of barley seedlings [43]. Due to the effect of clomazone in the reduction of the antenna pigments (LHCII), an excessive influx of the excitation ABS is transferred into the active reaction centre (RC) of the photosystem II according to Kaň a et al. [43]. During this process, the formation of the reactive singlet oxygen 1 O 2 via the 3 Chl * was excepted according to Fufezan et al. [4], especially with the reduction of the carotenoids which have an important role in protecting the chlorophyll from photooxidation during the plant growth [44]. ...
... Using 1/100 of the recommended dose, the young plants were more affected. Indeed, their cane weight was significantly lower after exposure with 2,4-D (50%), chlorsulfuron (50%), thifensulfuron (30-40%) or glyphosate (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40). In the meantime, the established grapevines were only affected by 2,4-D, which generated a 40% reduction of the cane weight the first year and 30% the following year. ...
... In addition, the transpiration and the dark respiration rates decreased by 28 and 63% respectively. The pre-emergence herbicide clomazone (isoxazolidinone) used on wheat seedlings reduced concomitantly the photosynthetic rate and the carotenoid content by more than 50% and the chlorophyll content by 70% in primary leaves [36]. Several aminophosphonate herbicides used on cucumber at a concentration of 0.25 mM caused a decrease of the chlorophyll content by 30 to 55% [37]. ...
Crops undergo many biotic stresses such as the competition with weeds or the attack by various microorganisms, insects, nematodes… At present, the use of agrochemicals is the main strategy to limit these biotic stresses but this can generate a dramatic alteration of plant health and a subsequent loss of yield. Among the different classes of products, herbicides, insecticides and fungicides are the most commonly used, corresponding to 90% of chemicals used in agriculture. New pesticides regularly appear on the market in order 1/ to improve the efficiency of chemical treatments, 2/ to limit the occurrence of resistant targets by a diversification of the active molecules and 3/ to preserve the environment by reducing soil and water pollutions. The new generation of chemicals is currently applied at low concentrations and has a less deleterious impact on the environment than in the past. However it was reported than many protection products still have negative obvious effects on crop physiology such as visible injuries (chlorosis, leaf necrosis, vein discoloration, terminal bud death…) and growth reduction. Beside their toxicity related to their specific target, several pesticides generate stress to crops which is reflected by an alteration of nitrogen and/or carbon metabolism leading to a lower nutrient availability for plant growth. Pesticides also perturb the development of the reproductive organs, which may have dramatic consequences on fruit and seed formation. In some cases, crops are capable to overcome the toxic effects of chemicals. Indeed it
was reported that agrochemicals, in particular fungicides, trigger different pathways of
plant defenses enabling crops to recover normal physiology and thus to counteract the
effect of chemical treatments. Nevertheless the induction of plant defense mechanisms is
not always sufficient to maintain an optimal plant growth. Whatever the mode of action
of pesticides, their side effects cause a decrease of yield in term of biomass, fruit/seed
quantity and/or quality. The overall side effects of chemicals on crops and environment,
as well as the putative presence of residues in harvested organs highlight the necessity to
commercialize less toxic pesticides and to develop alternative strategies for plant
protection (bio-control, elicitation), which can limit the damages caused by chemical
treatments.
... Although Norman et al. ( 1990 ) did not identify specifi c clomazone metabolites, they did note that up to 5.9% of recovered residues in the seeds of both soybean ( Glycine max ) and cotton ( Gossypium hirsutum ) were β-glucosides. Kana et al. ( 2004 ) investigated the photosynthetic capability of barley seedlings ( Hordeum vulgare ) that were cultivated on fi lter paper containing either 0.25 or 0.5 mM clomazone (12 days, continuous light, 10 °C). Adverse effects included a reduction in chlorophyll (a + b) and carotenoid levels. ...
... Adverse effects included a reduction in chlorophyll (a + b) and carotenoid levels. Kana et al. ( 2004 ) concluded that the photochemical processes in this species cannot operate fully due to pigment loss brought on by clomazone toxicity. Similarly, Yasuor et al. ( 2008 ) found clomazone and 5-ketoclomazone to illicit greater inhibition of chlorophyll a and carotenoids in susceptible populations of late watergrass ( Echinochloa phyllopogon ) than in resistant populations. ...
Clomazone, an isoxazolane herbicide, was first registered for use in 1986 for pest grasses and broadleaf weeds. Although the exact mode of action is still unclear, it is well documented that clomazone causes bleaching of foliar structures; the clomazone metabolite 5-ketoclomazone is regarded to cause the bleaching and to be the ultimate plant toxicant. Although clomazone exhibits low mammalian toxicity and is selective towards certain plant species, studies have shown that it does inhibit AChE and catalase activities. In addition, it has been found to be highly toxic to aquatic invertebrates, in particular mysid shrimp. Clomazone has a low Henry's law constant and moderate vapor pressure, and thus may volatilize from dry soils. Photolysis represents a minor dissipation pathway; however, clomazone can be photolytically degraded under both direct and indirect conditions. Clomazone has high water solubility, and it is often assumed to undergo hydrolysis easily; unfortunately, this is not the case. Clomazone is stable over a wide pH range and does not hydrolyze. Clomazone has a weak to moderate soil adsorption coefficient; therefore, its affinity to sorb to soil is minimal, rendering it a potential threat to groundwater supplies. Microbial metabolism is the major degradation pathway, resulting in products such as 5-hydroxyclomazone, hydroxymethylclomazone, 2-chlorobenzyl alcohol and 3'-hydroxyclomazone. Although clomazone has not been shown to degrade via hydrolysis, it nonetheless represents a potential threat to aquatic organisms. With this in mind, caution should be taken when applying clomazone or when draining fields that have detectable clomazone residues.
... Treatment of plants with MEP pathway-specific inhibitors, like fosmidomycin (FR-31564) or clomazone causes bleaching of the plant [45,242], by preventing formation of b-carotene which normally protects photosynthetic reaction centers from photooxidation [243]. But these compounds which reduce the synthesis of other end-products derived from MEP [244][245][246][247][248]. Characterization of fosmidomycin inhibition was made using bacteria [218,249]. ...
... In between, fosmidomycin was widely used to decrease MEP-derived isoprenoid production by several research teams and in different systems. For many years, clomazone, a synthetic chemical, has been utilized as an efficient bleaching herbicide [242,243,[251][252][253], without a clear idea of the nature of the target [254][255][256]. Interestingly, in cotton (Gossypium hirsutum L.), it inhibited phytol and carotenoid biosynthesis, but induced sesquiterpenoid accumulation [257]. ...
When compared to other organisms, plants are atypical with respect to isoprenoid biosynthesis: they utilize two distinct and separately compartmentalized pathways to build up isoprene units. The co-existence of these pathways in the cytosol and in plastids might permit the synthesis of many vital compounds, being essential for a sessile organism. While substrate exchange across membranes has been shown for a variety of plant species, lack of complementation of strong phenotypes, resulting from inactivation of either the cytosolic pathway (growth and development defects) or the plastidial pathway (pigment bleaching), seems to be surprising at first sight. Hundreds of isoprenoids have been analyzed to determine their biosynthetic origins. It can be concluded that in angiosperms, under standard growth conditions, C₂₀-phytyl moieties, C₃₀-triterpenes and C₄₀-carotenoids are made nearly exclusively within compartmentalized pathways, while mixed origins are widespread for other types of isoprenoid-derived molecules. It seems likely that this coexistence is essential for the interaction of plants with their environment. A major purpose of this review is to summarize such observations, especially within an ecological and functional context and with some emphasis on regulation. This latter aspect still requires more work and present conclusions are preliminary, although some general features seem to exist.
... Nicosulfuron is a photosynthetic system inhibitor and can reduce the content of chlorophyll and the ability of the plant to conduct photosynthesis by interfering with the rate of electron transport of the plants [17][18][19]. Spraying nicosulfuron affects the photosynthetic mechanism by altering the metabolism of plant cells, which results in the disintegration of chloroplasts and a change in the leaf color of plants. The photosynthetic pigments and photosynthetic-related protein activities of plants are significantly reduced, and nicosulfuron destroys the chloroplast structure [20][21][22]. ...
The sulfonylurea herbicide nicosulfuron is efficient, harmless and selective at low doses and has been widely used in maize cultivation. In this study, a pair of corn sister lines, HK301 (nicosulfuron-tolerence, NT) and HK320 (nicosulfuron-sensitive, NS), was chosen to study the effect of nicosulfuron on plant growth and sugar metabolism in sweet maize ( Zea mays L.) seedlings. All the experimental samples were subjected to treatment with water or 80 mg kg –1 of nicosulfuron when the sweet maize seedlings grew to the four-leaf stage. Nicosulfuron significantly inhibited the growth of NS line. The content of sucrose and the activities of sucrose phosphate synthase and sucrose synthase in the two inbred lines increased differentially under nicosulfuron stress compared with the respective control treatment. After nicosulfuron treatment, the activities of hexokinase and 6-phosphofructokinase and the contents of pyruvic acid and citric acid in NS line decreased significantly compared with those of NT line, while the content of sucrose and activities of sucrose phosphate synthase and sucrose synthase increased significantly. The disruption of sugar metabolism in NS line led to a lower supply of energy for growth. This study showed that the glycolysis pathway and the tricarboxylic acid cycle were enhanced in nicosulfuron-tolerant line under nicosulfuron stress in enhancing the adaptability of sweet maize.
... In contrast, the intercellular CO 2 concentration showed an increasing trend, indicating that the main reason for decreasing net photosynthetic rate is non-stomata limiting factors. In short, fomesafen affects the photosynthetic cells of sugar beet leaves, resulting in a decline in photosynthetic capacity (Tambussi et al., 2000;Kaňa et al., 2004;Chandrasena and Sagar, 2010). ...
Fomesafen is an herbicide used in soybean production, and sugar beet is a sensitive crop to fomesafen. When the herbicide is sprayed in the field, it is easy to cause floating and depositing on non-target crops, resulting in crop poisoning and reducing yield. There are few on the phenomenon and mechanism of fomesafen herbicide drift on sugar beet. There are few reports on the phenomenon and mechanism of ether herbicide migration on phytotoxicity of sugar beet. Therefore, in this experiment, indoor potted plants were used to simulate the dose of fomesafen drift deposited on sugar beet in the field to study the effects of fomesafen on the growth, photosynthetic system, and physiological indexes of seedlings for sugar beet were studied. The results showed that fomesafen at the dose of 225 g a.i. ha⁻¹ significantly inhibited the plant height, root length, and biomass of sugar beet. Compared with the control, the net photosynthetic rate, stoma conductance, transpiration rate, and total chlorophyll pigment content of leaves were reduced by 77.16%, 83.84%, 64.00%, and 28.13%, respectively. Treatment with a dose of 225 g a.i. ha⁻¹ also damaged the photosynthetic system II of the leaves, lowering the performance index on absorption energy, maximum quantum yield and, the energy of electron transfer, causing photoinhibition and photodamage. In addition, fomesafen significantly increased the content of malondialdehyde and the activity of peroxidase in leaves of sugar beet, reducing the activities of superoxide dismutase and catalase. Overall, this study is helpful to understand the drift and deposition of fomesafen on sugar beet and to discuss the phytotoxicity risk and dose of fomesafen on the beet, as a result of controlling the dose of fomesafen sprayed in the field.
... However, the increasing risk of phytotoxicity caused by pesticidal residue accumulation in non-targeted species as well as in soil, water (ground and surface) and air [11][12][13], leading to various human health issues [14], outweighs the benefits offered by the pesticides. Agrochemical application influences the seed germination potential and impacts a variety of physiological and biochemical processes, such as disrupting membrane integrity, enzyme function and nucleic acid damage [15,16]. ROS is considered as an index to depict cell damage. ...
Pervasive use of chlorpyrifos (CP), an organophosphorus pesticide, has been proven to be fatal for plant growth, especially at higher concentrations. CP poisoning leads to growth inhibition , chlorosis, browning of roots and lipid and protein degradation, along with membrane dys-function and nuclear damage. Plants form a linking bridge between the underground and above-ground communities to escape from the unfavourable conditions. Association with beneficial rhi-zobacteria promotes the growth and development of the plants. Plant hormones are crucial regulators of basically every aspect of plant development. The growing significance of plant hormones in mediating plant-microbe interactions in stress recovery in plants has been extensively highlighted. Hence, the goal of the current study was to investigate the effect of 24-epibrassinolide (EBL) and PGPRs (Pseudomonas aeruginosa (Ma), Burkholderia gladioli (Mb)) on growth and the antioxidative defence system of CP-stressed Brassica juncea L. seedlings. CP toxicity reduced the germination potential , hypocotyl and radicle development and vigour index, which was maximally recuperated after priming with EBL and Mb. CP-exposed seedlings showed higher levels of superoxide anion (O2 .−), hydrogen peroxide (H2O2), lipid peroxidation and electrolyte leakage (EL) and a lower level of nitric oxide (NO). In-vivo visualisation of CP-stressed seedlings using a light and fluorescent microscope also revealed the increase in O2 .− , H2O2 and lipid peroxidation, and decreased NO levels. The combination of EBL and PGPRs reduced the reactive oxygen species (ROS) and malondialde-hyde (MDA) contents and improved the NO level. In CP-stressed seedlings, increased gene expression of defence enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APOX), glu-tathione peroxidase (GPOX), dehydroascorbate reductase (DHAR) and glutathione reductase (GPOX) was seen, with the exception of catalase (CAT) on supplementation with EBL and PGPRs. The activity of nitrate reductase (NR) was likewise shown to increase after treatment with EBL and PGPRs. The results obtained from the present study substantiate sufficient evidence regarding the positive association of EBL and PGPRs in amelioration of CP-induced oxidative stress in Brassica juncea seedlings by strengthening the antioxidative defence machinery. Citation: Bakshi, P.; Chouhan, R.; Sharma, P.; Mir, B.A.; Gandhi, S.; Landi, M.; Zheng, B.; Sharma, A.; Bhardwaj, R. Effect of Chlorpyrifos-Induced Toxicity in Brassica juncea L. by Combination of 24-Epibrassinolide and Plant-Growth-Promoting Rhizobacteria.
... We can evaluate the damage of herbicides to crops by morphological and physiological indicators. Plenty of herbicides act by inhibiting with the ETR where interfere photosynthesis, or by reducing the number and changing structure of plant chloroplast thylakoids in plants under herbicides (Kaňa et al. 2004). Zheleva et al. (1994) reported that atrazine destroyed the D1 protein and caused a change in the structure of the PSII to block electron transfer. ...
Acetochlor is always used in maize (Zea mays L.) fields as a common pre-emergence herbicide. In this field study, we investigated the effects of acetochlor on the photosynthetic characteristics, chlorophyll fluorescence parameters, and antioxidant enzyme activities in acetochlor-resistant (BWC95) and acetochlor-sensitive (BWC12) near-isogenic lines. We sprayed acetochlor after sowing, using water treatment as the control. After spraying acetochlor, the net photosynthetic rate, stomatal conductance, transpiration rate, and the function of chloroplasts were significantly lower in BWC12 than BWC95, whereas the intercellular CO2 concentrations and stomatal limitation values were higher. In addition to nonphotochemical quenching, chlorophyll fluorescence measurements obtained using leaves showed that the maximum photochemical efficiency of photosystem II (PSII), actual photochemical efficiency of PSII, photochemical quenching of chlorophyll fluorescence, and electron transport rate were higher in BWC95 than BWC12 after acetochlor treatment. H2O2 and O2˙⁻ levels were higher in BWC12 than BWC95, which resulted in severe membrane lipid peroxidation due to sustained oxidative stress. Thus, the malondialdehyde content increased significantly with the exposure time in BWC12, and the antioxidant enzyme activities were lower in BWC12 than BWC95. The results show that acetochlor resistance is directly related to a high photosynthetic rate and a protective antioxidant enzyme system.
... Valuable trees may thus be affected by herbicide drift. Many herbicides inhibit PSII (Oettmeier, 1999): atrazine prevents electron transfer to the proton quinone pool though binding the D1 protein of PSII (Rutherford & Krieger-Liszkay, 2001); clomazone depresses electron transport in chloroplasts thylakoid membrane (Kaňa et al., 2004); acetochlor reduces the photochemical efficiency of PSII in terms of both light-induced and NPQ (Tan et al., 2012); flumioxazin inhibits protoporphyrin oxidase, reducing the net photosynthetic rate and GS levels of grape leaves (Bigot et al., 2007). We studied both glyphosate and GLA because their modes of action differ. ...
... It acts as a sulfur transporter in xenobiotic detoxification. Glutathione serves various vital roles in cells such as ROS scavenging, Yoo et al. (2006) Hordeum vulgare DCMU Photobleaching Barry et al. (1990) Clomazone Reduced chlorophyll and carotenoids, reduced rate of CO 2 assimilation Kaňa et al. (2004) Solanum tuberosum Imadacloprid (insecticide) ...
The way to technology-based era accelerates the rate of industrialization, intensive agriculture, use of herbicides/pesticides, and fossil fuel burning that not only disturb the natural vegetation but also increase the contamination of natural resources and accumulation of organic and inorganic pollutants in the soil and in water. Organic pollutants (OPs) are persistent in biota since metabolism is slow and therefore accumulates in the food chain, thereby causing damage to plants and animals. There are reports for the existence of several detoxification mechanisms in plants, among which conjugation with glutathione is one of the important detoxification pathway for OPs. In this process, glutathione S-transferases (GSTs) play a vital role and mediate the conjugation of OPs to reduced glutathione (GSH) followed by compartmentalization of conjugates within vacuole/apoplast through the action of ATP-dependent pumps and their subsequent metabolism in plants. Present paper deals in details on the role of glutathione in enhancing tolerance of plants against organic pollutants.
... Related to young leaves, F v /F m decreased significantly at the concentration (1 μM) (F v /F m = 0.279 (Virginie); F v /F m = 0.454 (Xanthi). This result don't corresponds with result ofKaňa et al. (2004) showing that clomazone cause a small reduction not significant in F v /F m , and with results ofDuke and Kenyon (1986), who observed no direct effect of clomazone on electron transport in PSII. In addition, the performance index (PI abs ) had provided information on the seedlings tobacco's state treated with clomazone. ...
Les effets de faibles doses de clomazone 2-(2-chlorobenzyl)-4,4-dimethyl-1,2-oxazolidin-3-one, un herbicide non-sélectif de la famille des isoxazolidinones, ont été étudiés chez Nicotiana tabacum L. De faibles concentrations de clomazone (1, 0.1, 0.01, 0.001, 0.0001 et 0.00001 µM), ont été appliquées chez deux variétés de tabac (Nicotiana tabacum L. cv. Xanthi; Nicotiana tabacum L. cv.Virginie vk51) cultivées en hydroponie. Le transport d'électrons photosynthétiques a été étudié par l'analyse de la cinétique rapide de fluorescence chlorophyllienne et par la mesure de l'évolution de l'oxygène chloroplastique. Les résultats ont montré que le clomazone à des concentrations de 1, 0.1, 0.01, 0.001et 0.0001 µM, affecte les paramètres JIP (Fv/Fm, PIabs, 1–VJ, ABS/RC, TR0/RC, DI0/RC, ET0/RC et ET0/ABS). Le clomazone à une concentration de 1 µM, conduit à une importante accumulation de H2O2 chez Virginie induisant la mort cellulaire programmée (PCD). Nos résultats montrent que la variété Xanthi présente une tolérance plus importante au clomazone que la variété Virginie, ce qui peut s'expliquer par une meilleure efficacité du transport d'électrons au delà de QA, ainsi qu'une amélioration du fonctionnement du système antioxydant enzymatique (APX et MDHAR). Le prétraitement des plantules de la variété Virginie par une alternance de cycles courts de lumière/obscurité (16 min/ 8min) pendant trois jours lorsque les plantules sont au stade de trois feuilles, a amélioré leur tolérance face à la toxicité du clomazone. Ce prétraitement induit l'activation des systèmes de détoxification des ERO via l'augmentation des activités des enzymes antioxydants et la biosynthèse de composés antioxydants tels que l'ascorbate et les composés phénoliques et réduit le niveau de mort cellulaire programmée, induit par le stress photooxydatif. Il est supposé que la stimulation des voies alternatives de dissipation des électrons, telle que la photorespiration, ainsi que les modifications du cycle circadien, soient prioritairement impliquées dans l'acquisition de la tolérance. Cet effet dit de "priming" se maintient tout au long de la croissance du tabac et se manifeste par une augmentation de la croissance et de la photosynthèse nette qui perdure jusqu'au stade de la floraison.
... As a result of this, these compounds remain in environment for long period and affect the biotic component of nature, contaminate food, health hazards, etc. In plants, pesticide toxicity results in chlorosis, necrosis, vein discoloration which affects plant growth and development negatively (Kana et al. 2004). ...
Application of pesticides to enhance productivity is a common practice in agricultural field. Pesticides no doubt play an important role in protecting the majority of crops from the pests and enhancing yield but extensive use of pesticides is a major concern today due to its presence at various trophic levels as well as in drinking water. They pose detrimental effects on the survival of wildlife, plants, animals, aquatic ecosystem as well as other non‐target species. They are considered as chemical mutagens in animals are resulting in mutations, damage of genetic material and chromosomal aberrations which are life threatening. Necrosis, chlorosis, stunted growth, etc. are common phytotoxic symptoms of pesticides in plants. Detoxification of pesticides is possible by various physico‐chemical as well as biological techniques. Physico‐chemical methods include detoxification systems which are very costly, laborious, and time consuming. Biological techniques use living biota which is eco‐friendly technique. The present review makes an approach to emphasize on physico‐chemical methods as well as biological methods including use of microbes and plants.
... A 33% reduction of the net leaf photosynthesis and a 60% increase in the stomatal resistance were registered (Bhatti et al. 1997). The pre-emergence herbicide clomazone (isoxazolidinone) used on wheat seedlings reduced concomitantly the photosynthetic rate and carotenoid content by more than 50% and the chlorophyll content by 70% in primary leaves (Kaňa et al. 2004). Six-week-old grapevines grown in vitro were exposed to the herbicide flumioxazin (N-phenylphthalimide) at a lower concentration than in the field (Saladin et al. 2003b). ...
Environmental pollution has become one of the major problems on this planet in the last few decades. Environmental organic pollutants (OPs) particularly have an immense effect on the growth and development of plants. The group of organic chemicals discussed here include the pesticides, antibiotics, bisphenol A (BPA) and polycyclic aromatic hydrocarbons (PAHs). They are quite persistence in the environment and may take several decades or even centuries to degrade. OPs have been found in tissues or environmental samples from almost all parts of the world. Because of their unique physicochemical characteristics, OPs are either adsorbed on atmospheric particles or exist in the vapor phase, which facilitates their transport over large distances in the atmosphere. Toxic OPs can be taken up by plants through roots and foliage. In this chapter we have summarized the effects of OPs on various steps of photosynthesis. OPs have the potential to influence the primary processes of photosynthesis, particularly PSII complex. Chlorophyll a fluorescence is used as an indicator to assess toxicity of OPs on plants and algae. This technique and its interpretations can be applied to monitor the effects of environmental pollutants on varied samples like higher plants, algae, etc. Based on the literature, we conclude that these pollutants have a potential risk to plant growth and crop yield through inhibition of the light reaction as well as the dark reaction of photosynthesis. An improved understanding of these factors will allow the planning of strategies to reduce the harmful impacts of pollutants.
... In agreement with these findings, Darwish et al. (2013) found a reduction on the contents of photosynthetic pigments in tobacco plants as the clomazone concentration increased, while Kana et al. (2004) found that the herbicide reduced the formation of pigment-protein compounds on the thylakoid membranes. Injuries resulting from increasing doses of clomazone were also verified by Andres et al. (2013) in different irrigated rice cultivars, with later recovery of the plant. ...
The pre-treatment of rice seeds with sodium nitroprusside (SNP) was used to investigate the effect of exogenous nitric oxide on the pigment content and the activity of antioxidant enzymes during the inhibition of the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway by the herbicide clomazone. The seeds were soaked in SNP solution (200 mM) for one and 10 hours and sprayed with clomazone, at post-seeding and at the needle-point, with 612 (experiment 1) and 1,224 g a.i. ha-1 (experiment 2). The control of both factors received distilled water. Carotenoids, chlorophylls a, b and total, superoxide dismutase (SOD), guaiacol peroxidase (POD) and the correlation between the variables were evaluated in the shoot of the plants. When compared to the control (no SNP), the imbibition for one hour increased carotenoid and total chlorophyll content by 24 and 54%, respectively, in experiment 1, where clomazone was applied in post-seeding. In the absence of the herbicide, the values were 37 and 59% higher. The SOD and POD activity, respectively, was increased by 48 and 51%, when the seeds were soaked for 10 hours and exposed to 612 g a.i. ha-1 of clomazone in post-seeding application. In a similar condition, in experiment 2, there were no changes in enzyme activity. Seed pretreatment with SNP increases the carotenoid and chlorophyll contents in rice plants, even with the inhibition of the MEP pathway by clomazone. The behavior of the SOD and POD activity indicates that other mechanisms besides the increase in the photosynthetic pigment contents are involved in the detoxification of the reactive oxygen species induced by the mode of action of clomazone.
... After several works, it has been demonstrated that these enzymes are not inhibited by clomazone, leaving the possibility that a clomazone metabolite produced in vivo is the true inhibitor or that the site of inhibi- tion is outside the carotenoid biosynthesis route (Mueller et al. 2000). It is possible that some of these metabolites are converted to toxic form in plants ( Devine et al. 1993;Kańa et al. 2004). ...
Weeds infest crop fields and adversely affect the growth and yield of crop plants. Eradication of weeds from agricultural lands is often labour-extensive and economically expensive. Recent approaches used to control weeds include physical, cultural, chemical and biological methods. Chemical control through herbicides is an instant and effective remedy for weed control. However, there are reports on development of herbicide resistance in weeds possibly due to restricted bioavailability of herbicides in plants. Further, the extensive usage of toxic chemicals contaminates the environment and poses health threats to humans and animals. Efforts to design suitable nanoparticles (NPs) carrying herbicides offer a promising hope in the control of unwanted plant species. Such approaches include synthesis of NPs, nanoemulsions, nanoencapsulation, etc. Nanoherbicides not only reduce the herbicide load on the environment but also help in eradication of weeds without leaving any major toxic residues in soils and environment. These herbicide-loaded ‘nano-bullets’ can effectively target the specific plant organ or tissue with a controlled herbicide release. This approach of weed control costs less and ensures minimum toxicological implications besides increasing the herbicide bioavailability into weeds. We discuss here briefly the weed maniac and the strategies for its control and provide a detailed account of synthesis and applications of nanoherbicides with special emphasis on their bioavailability, distribution and the possible mechanisms of action in plants.
... They reported that paraquat caused a decrease in chlorophyll (a+b) and carotenoid content at high concentrations. Kana et al. (2004) analysed the effects of the herbicide clomazone on photosynthesis, which was applied before germination to barley (Hordeum vulgare L.) leaf. They observed that increased concentrations of clomazone caused a decrease in chlorophyll (a+b) and carotenoid levels. ...
Glyphosate is an herbicide that is applied after non-selective germination and affects plant growth. In this study, glyphosate was applied to Zea mays L. after germination, at a concentration range from 0.017 to 0.145 M in a growth chamber. The effects of this herbicide on some antioxidant enzymes, lipid peroxidation, total chlorophyll and total carbohydrate content were investigated on days 1, 5 and 10 following the application. Results showed that peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) were increased in the groups treated with glyphosate on days 5 and 10, but the activities of reduced glutathione (GSH) and glutathione reductase (GR) were decreased on day 10. Malondialdehyde (MDA) content indicating lipid peroxidation was increased on days 1, 5 and 10. Changes in total chlorophyll and total carbohydrate contents were found to be time-dependent. These increases and decreases in the antioxidant activities, MDA content, total chlorophyll and total carbohydrate content in Zea mays L. were determined as a symptom of cytotoxicity caused due to glyphosate.
... Pesticides cause toxicity to plants by means of chlorosis, necrosis and vein discolouration, leading to retarded growth and development by reducing photosynthetic efficiency, nitrogen and carbon metabolism (Kaňa et al., 2004). Pesticide application was also reported to inhibit photosynthesis by negatively affecting the plant photosystems (Xia et al., 2006). ...
To protect crops from pests, pesticides are used. Pesticides also cause toxicity to crop plants
and persist in plant parts in the form of pesticide residues. Brassinosteroids (BRs) are known
for their protective role in plants under various abiotic stresses like heavy metal, drought,
temperature, pesticide etc. BRs ameliorate pesticide toxicity in intact plants by activating the
antioxidative defence system. BRs also enhance the degradation of pesticides that leads to
reduction in pesticide residues in plant parts. Present review gives an updated information
about the protective roles of BRs in plants and the underlying mechanisms under pesticide
stress.
... B. juncea L. is attacked by various pests like aphids, cut worms, leaf hoppers, and so on, which are generally controlled by pesticides (Rabbinge & Oijen 1997), with imidacloprid (IMI) being the most effective pesticide against the above pests (Ko et al. 2014). But pesticides also cause toxicity to the plants leading to retarded growth, degradation of photosynthetic pigments, reduced photosynthesis and declined protein content (Kaňa et al. 2004;Sharma et al. 2015Sharma et al. , 2016aSharma et al. , b, 2017a. Brassinosteroids (BRs) are reported to enhance the growth as well as the protein content of plants under heavy metal and pesticide (Arora et al. 2010;Hayat et al. 2012;Sharma et al. 2015). ...
Pesticides are applied to protect crops from a variety of insect pests but their application cause toxicity
to plants that results, among others, in reduction of protein as well as amino acid contents. The present
study is aimed at observing the effect of seed pre-soaking with 24-epibrassinolide (EBL) on the protein and
amino acid content in the leaves of Brassica juncea L. grown in soil that is amended with pesticide im-
idacloprid (IMI). Soil amendment with IMI resulted in a decrease in the contents in leaves of total proteins
and 21 amino acids studied. Seed soaking with 100 nM of EBL resulted in the recovery of total protein as
well as amino acid contents in leaves, when compared with plants grown in only IMI amended soils.
... Under the effect of the clomazone action, the total chlorophyll content is more impaired than the photochemical effectiveness, possibly because the herbicide molecule damages the formation of the chlorophyll pigment and not the transportation of electrons. Kana et al. (2004) studied the photosynthetic capacity of barley (Hordeum vulgare) seedlings, cultivated in filter-paper containing 0.25 and 0.5 mM of clomazone, under 12 days of continuous light, and verified reductions in the total content of chlorophyll and also in the levels of carotenoids. They concluded that the photochemical processes in this species cannot fully work, due to the loss of pigments caused by the herbicide intoxication. ...
The use of indicator plants can be an effective alternative in monitoring the presence of toxic molecules in the air, such as herbicides. Thus, in the goal of this study is to assess the sensitivity of forage plants and weeds to atmospheric residual concentrations of clomazone. The treatments were arranged in a 6x5 factorial scheme, with the first factor corresponding to the plant species triticale (Triticosecale rimpaui), maize (Zea mays), sorghum (Sorghum bicolor), palisade grass (Urochloa brizantha), purslane (Portulaca oleracea) and signal grass (Urochloa decumbens), and the second factor to doses of 0, 90, 180, 270 and 360 g ha-1 clomazone doses (equivalent to atmospheric concentrations of 0.0, 0.05, 0.10, 0.15 and 0, 20 mg L-1). Twelve days after emergence, the plants were allocated inside experimental rectangular chambers with a volume of 500 dm3, covered by 150 uM of transparent polyethylene film. The plants remained exclusively in the chamber atmosphere with the herbicide for a period of 96 hours. After the chambers were opened, there were the first evaluation of intoxication and chlorophyll content, as well. The evaluations were repeated on day 7 and 14 after the chamber opening. The presence of clomazone in minimal concentrations in the atmosphere affected the quality of the evaluated plants. Signal grass, palisade grass, sorghum, triticale and purslane were sensitive to atmospheric residual concentrations of clomazone and they can be used to monitor the air quality when there are wastes from this molecule.
... Fv/Fm parameter was measured on whole cells previously dark adapted for 20 min. Fv/Fm measurements were performed using a video-imaging system as in [76,77]. ...
... Fv/Fm parameter was measured on whole cells previously dark adapted for 20 min. Fv/Fm measurements were performed using a video-imaging system as in [76,77]. ...
Microalgae are fast-growing photosynthetic organisms which have the potential to be exploited as an alternative source of liquid fuels to meet growing global energy demand. The cultivation of microalgae, however, still needs to be improved in order to reduce the cost of the biomass produced. Among the major costs encountered for algal cultivation are the costs for nutrients such as CO2, nitrogen and phosphorous. In this work, therefore, different microalgal strains were cultivated using as nutrient sources three different anaerobic digestates deriving from municipal wastewater, sewage sludge or agro-waste treatment plants. In particular, anaerobic digestates deriving from agro-waste or sewage sludge treatment induced a more than 300% increase in lipid production per volume in Chlorella vulgaris cultures grown in a closed photobioreactor, and a strong increase in carotenoid accumulation in different microalgae species. Conversely, a digestate originating from a pilot scale anaerobic upflow sludge blanket (UASB) was used to increase biomass production when added to an artificial nutrient-supplemented medium. The results herein demonstrate the possibility of improving biomass accumulation or lipid production using different anaerobic digestates.
... ha À 1 , the IMI residues (including its metabolites) detected after 30 and 60 days of treatment were 1.60 and 0.90 mg Kg À 1 soil respectively. Pesticides also cause toxicity to the plants resulting in retarded growth, decreased photosynthetic pigments (Huiyun et al., 2009;Singh et al., 2016) and adversely affect their photosynthetic performance (Kaňa et al., 2004;Xia et al., 2006;Wang et al., 2016). ...
... An effect on oil seed rape can be observed for the clomazone treatment on barley (Command-barley, Figure 3 top right), while there is only an effect on barley for the highest dosages. According to Kaňa et al. (2004), clomazone treatments inhibit pigment synthesis also in barley. The plant height level of barley was at the same level over the whole plot, as the height measurements show. ...
Many different sensors have been proposed to estimate plant status parameters like nutrition status, coverage or plant size. Such parameters are key factors for precise management. This study combined four different sensors in a field trial with spring barley and oil seed rape. The following commercial sensors were used: LiDAR, spectrometer, ultrasonic device, and a commercial opto-electronic device. Spectral indices were calculated from the spectrometer and opto-electronic devices, and plant height from the ultrasonic and LiDAR sensors. A robotic software framework was used for simultaneous measurements with multiple sensors. The fusion of features from multiple sensors permitted the estimation of health status parameters for sensitive plants in a herbicide stress trial.
... Cohen and Li (1996) reported a positive correlation between the flow of water in the plant and leaf area. Application of measurements of gas exchange to determine the effect of herbicides on plant physiological manifestations can be considered as a standard method (Ferrell et al. 2003, Kaňa et al. 2004. Literature data about the sap flow method usage for the determination of the effect of herbicides on plant transpiration demands are not available. ...
Physiological parameters are sensitive and provide information on the toxicity of herbicides in plants. The impact of herbicide application on plant transpiration was evaluated by the sap flow method during 2009-2011. The aim of this work was to verify the sap flow method for determining the effect of herbicides on the basis of continuous measurements of the transpiration flow. Helianthus annuus was used as a model plant species. The two different herbicides tested in this study differed by the effect of active ingredients bromoxynil and clopyralid. The water flow was measured using sap flow meter T4.2. The impact of herbicides was assessed by comparing measured transpiration rate (Q) after herbicide application with an extrapolation of transpiration rate of plants before herbicide treatment (Q(calc)). After treatment with bromoxynil the Q values decreased significantly compared to Q(calc). For plants treated by clopyralid, the decline of actual transpiration (Q) compared with the modelled one (Q(calc)) was less substantial and the plants continued to transpire after the treatment. The effect of herbicides was also verified using infrared gas analyser and chlorophyll fluorescence meter.
... However, no previous research has demonstrated total carotenoids as a degree of severity indicator of bleaching symptoms on susceptible plant material (Creech et al. 2004;Kana et al. 2004). Kim et al. (2004) reported that the death mechanism of plants treated with carotenoid biosynthesis inhibiting herbicides is different depending on the developmental stage of the plant. ...
... Indeed, herbicidal application of clomazone affected the photosynthetic apparatus of barley (Hordeum vulgare L.) by reducing the levels of chlorophylls and carotenoids, which resulted in a reduction of photosynthetic electron rate [39]. Interestingly, clomazone did induce a small amount of electrolyte leakage within a similar period of incubation [24], which may be due to a more rapid effect on the high turnover of chlorophyll phytylation rather than the relatively slower reduction in plastoquinone pool. ...
... These compounds have negative effect on various physio-morphological attributes such as visible injuries (chlorosis, necrosis, vein discoloration) and reduction in growth and biomass. They cause inhibition of photosystems and photosynthetic pigments thereby decreasing the photosynthetic efficiency and alter nitrogen and/or carbon metabolism leading to their lower availability for plant growth (Kana et al., 2004). They also hamper the development of reproductive organs, which greatly damage fruit and seed formation (Saladin and Clement, 2005). ...
In this study, three cultivars and seven tetraploid potato clones were evaluated for two years in two cultivation systems (CS): without chemical protection against late blight development (NP) and with chemical protection (P). The objective of this study was to quantify the effect of chemical protection on the level of total carotenoids (TC) and individual carotenoids in potato tubers. The presented study showed that the content of TC in potato tubers is significantly affected by the CS and genotype. TC were higher in the system NP (mean 329.6 µg/100 g fresh weight [FW]) than in the system P (mean 206.2 µg/100 g FW). Although the development of late blight was observed only in the year 2019, a higher content of TC was observed in the system NP in both years. This dependence clearly show that CS without chemical protection favor carotenoids accumulation in potatotubers. In the case of lutein, the year had a significant impact on the concentration. The concentration of lutein in 2018 for the majority genotypes was higher (mean 72.1 µg/100 g FW), than in year 2019 (mean 37.3 µg/100 g FW), when late blight development wasobserved. The sharp decrease in lutein content in 2019 was probably caused by the development of late blight. A significant decrease of lutein content in potato tubers was observed in 2019 for all genotypes in system P and for five genotypes in system NP. It can be assumed that resistance mechanisms that occur during infection may have disturbed the accumulation of lutein in potato tubers.
The effect of carbamine insecticide on the productivity parameters of the Pisum sativum have been studied. The insecticide has decreased the photosynthetic pigments for all the concentrations. Nitrogen and protein content has initially decreased upto 14 days treatment period and has further increased during last 7 days. The soil nutrients (nitrate, sulphate & phosphate) have also decreased for all the concentration of the insecticide.
Recently, nanomaterials have been increasingly applied to improve the bioactivity of pesticides for plant protection. However, the incorporation of nanomaterials into nano-herbicides is still in the early stage of development. In this study, the effect of GO-GLY nanocomposites was tested on wheat and edible rape seedlings in terms of growth parameters, photosynthises, the activity and gene expression of antioxidant enzymes. The results showed that compared with GO or GLY alone, GO-GLY nanocomposite more significantly inhibited the growth of wheat and rape seedlings, decreased the net photosynthetic rate, stomatal conductance, transpiration rate, primary maximum photochemical efficiency of photosystem II, actual quantum yield and photosynthetic electron transport rate, while significantly increased the intercellular CO2 concentration. These changes may be related to increases in oxidative stress, as indicated by the higher accumulation of O2.− and H2O2 under GO-GLY treatment. Furthermore, GO-GLY treatment increased the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in both plant species compared with GO or GLY alone. In addition, gene expression analysis revealed that GO-GLY treatment upregulated the transcription of CATs, APXs, MDHAR, and DHAR genes in wheat seedlings, and elevated that of CATs, APXs, MDHAR, DHAR, and GR genes in rape seedlings compared with GO or GLY alone. Ultimately, in response to GO-GLY stress, a preliminary regulatory mechanism was proposed for the self-protective mechanism of wheat and rape seedlings, which lays a theoretical foundation for the wide application of nano-herbicides.
About book: This new volume examines the ecological importance, threats, protection, and management of the biodiversity of freshwater ecosystems, such as lakes, ponds, rivers, streams, reservoirs, pools, and wetlands. As populations have been increasing exponentially, human are using freshwater ecosystems severely, resulting in habitat destruction and breakdown. Environmental contamination, climate change, the introduction of harmful and invasive organisms, unplanned dredging and de-weeding processes, disposal of sewer systems in freshwater bodies, and badly planned water diversions are the leading causes of habitat loss in freshwaters. These impacts have led to significant decreases in the numbers and productivity of many freshwater species and decreased biodiversity in freshwater.
This book presents a selection of primary research and review papers on several freshwater aquatic biodiversity studies, which involve evaluating plants, macroinvertebrates, macrophytes, benthic zones, and fish diversity in freshwater ecosystems. It provides an abundance of new information on freshwater biodiversity distribution, status, and patterns.
Key features:
Discusses the importance, threats, and management of biodiversity of freshwater ecosystems
Provides detailed coverage of modern and updated techniques used in the evaluation and conservation of freshwater biodiversity,
Looks at the impact of pesticides pollution in freshwater environs on aquatic and terrestrial life
Reviews how global climate change affects freshwater biodiversity
Biodiversity of Freshwater Ecosystems: Threats, Protection, and Management promotes the enhancement and strengthening of freshwater protection and its unique biodiversity for scientists, policymakers, scholars, researchers, NGOs, and the public, providing necessary background knowledge and practical tools to help manage aquatic ecosystems and their biodiversity in a holistic manner.
Nicosulfuron is an ingredient in photosynthesis-inhibiting herbicides and has been widely used in corn post-emergence weed control. In the current study, a pair of sister lines, HK301 (nicosulfuron-tolerence, NT) and HK320 (nicosulfuron-sensitive, NS), was used to study the effect of nicosulfuron in sweet maize seedlings on C4 photosynthetic enzymes and non-enzymatic substances, expression levels of key enzymes, and chloroplast structure. Nicosulfuron was sprayed at the four-leaf stage, and water was sprayed as a control. After nicosulfuron treatment, phosphoenolpyruvate carboxylase (PEPC), NADP-malic dehydrogenase (NADP-MDH), NADP-malic enzyme (NADP-ME), pyruvate orthophosphate dikinase (PPDK), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities of NT were significantly higher than those of NS. Compared to NT, malate, oxaloacetic acid, and pyruvic acid significantly decreased as exposure time increased in NS. Compared to NS, nicosulfuron treatment significantly increased the expression levels of PEPC, NADP-MDH, NADP-ME, PPDK, and Rubisco genes in NT. Under nicosulfuron treatment, chloroplast ultrastructure of NS, compared to that of NT, nicosulfuron induced swelling of the chloroplast volume and reduced starch granules in NS. In general, our results indicate that in different resistant sweet maize, C4 photosynthetic enzymes activity and key genes expression play a critical role in enhancing the adaptability of plants to nicosulfuron stress at a photosynthetic physiological level.
Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122:121-158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additional Chl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F V /F M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge from different Chl a fluorescence analysis domains, yielding in several cases new insights.
On the basis of study on the mechanism of action of sulfonylurea herbicides, nine sulfonylurea derivatives of isoxazolidinone were designed and synthesized. The structures of these compounds were confirmed by means of IR, MS, NMR and elemental analysis. The results of preliminary active tests indicate that the compounds have some herbicidal activity. The structure-activity relationship was also studied.
This review represents systematic and integrated picture of pesticide exposure to plant and its effect on growth and metabolism. Decades ago, agrochemicals were introduced aiming at enhancing crop yields and protecting crops from pests. Due to adaptation and resistance developed by pests to chemicals, every year higher amounts and new chemical compounds are used to protect crops, causing undesired side effects and raising the costs of food production. Biological chemical free agriculture is gaining also more and more support but it is still not able to respond to the need for producing massive amounts of food. The use of agrochemicals, including pesticides, remains a common practice especially in tropical regions and South countries. Cheap compounds, such as DDT, HCH, and Lindane, that are environmentally persistent, are today banned from agriculture use in developed countries, but remain popular in developing countries. As a consequence, persistent residues of these chemicals contaminate food and disperse in the environment. Therefore, the thrust of this paper was to review the application of pesticides effect early from germination to growth of the plant, leading to alteration in biochemical, physiological and different enzymatic and non-enzymatic antioxidants which ultimately affect the yield and resulted in residues in plant, vegetables, and fruits.
The objected was to assess the relationship of physiological parameters to the susceptibility of Emilia
coccinea to a mixture of ametryn and clomazone applied post-emergence. The herbicide mixture was
applied in four doses 30 days after sowing (DAS). The physiological parameters studied were
photosynthetic pigments, chlorophyll fluorescence, soluble proteins, superoxide dismutase (SOD)
activity, ascorbate peroxidase (APX) activity, electrolyte leakage and lipid peroxidation (MDA) 72 hours
after application (HAA). Twenty-five days after application, the frequency of dead plants and dry matter
accumulation per plant were recorded. The data were analyzed by analysis of variance and linear or
nonlinear regression analysis. The total chlorophyll content (CHL), carotenoids (CAR) and maximum
quantum efficiency of PSII (Fv / Fm) decreased exponentially with increasing doses of the herbicide
mixture. The SOD activity decreased linearly. There was no significant linear increase in APX activity.
There were linear increases in the electrolyte leakage and lipid peroxidation with increased doses of the
mixture. In relation to plant mortality, a dose of 10 L ha-1 eliminated 100% of the E. coccinea population.
Given these observations, we conclude that the membrane damage appeared 72 HAA of a mixture of
clomazone + ametryn was closely related to mortality at 25 DAS.
A novel type of acetohydroxyacid synthase inhibitors, 4-methyl-3-isoxazolidinone derivatives of sulfonylurea, was designed and synthesized. The structures of these compounds were confirmed by using MS, NMR, and elemental analysis. The results of preliminary active tests indicate that the compounds show a herbicidal activity.
Acetochlor and fluoroglycofen are herbicides used in vineyards to eradicate weeds. This present study characterized the effects of these chemicals on photosynthetic characteristics and the antioxidant enzyme system in non-target grape leaves. The results showed that acetochlor and fluoroglycofen reduced net photosynthetic rate in a dose-dependent manner, but also reduced or increased pigment contents, respectively. According to chlorophyll fluorescence measurements, acetochlor and fluoroglycofen decreased the photochemical efficiency of photosystem II in the light and increased non-photochemical quenching. These herbicides enhanced malondialdehyde contents and accelerated the superoxide anion production rate in dose-dependent manners, which might be associated with lower antioxidant enzyme activities, especially at higher concentrations of the herbicides. Acetochlor and fluoroglycofen inhibited grapevine growth in the growth season one-year after herbicide treatment, and stem height was inhibited by up to 55.4% and 88.0%, respectively. Taken together, these results suggest that both herbicides are detrimental for grape photosynthesis and this might be associated with increased oxidative stress in the first year, while growth inhibition in the second year might be due to after effects of herbicide treatment.
This review represents systematic and integrated picture of pesticide exposure to plant and its effect on growth and metabolism. Decades ago, agrochemicals were introduced aiming at enhancing crop yields and protecting crops from pests. Due to adaptation and resistance developed by pests to chemicals, every year higher amounts and new chemical compounds are used to protect crops, causing undesired side effects and raising the costs of food production. Biological chemical free agriculture is gaining also more and more support but it is still not able to respond to the need for producing massive amounts of food. The use of agrochemicals, including pesticides, remains a common practice especially in tropical regions and South countries. Cheap compounds, such as DDT, HCH and Lindane, that are environmentally persistent, are today banned from agriculture use in developed countries, but remain popular in developing countries. As a consequence, persistent residues of these chemicals contaminate food and disperse in the environment. Therefore, the thrust of this paper was to review the application of pesticides effect early from germination to growth of the plant, leading to alteration in biochemical, physiological and different enzymatic and non-enzymatic antioxidants which ultimately affect the yield and resulted in residues in plant, vegetables, and fruits.
Chlorophyll fluorescence-based methods have been used for many years to study the effect of environmental factors (including herbicides) on plants, and, with the development of very sensitive fluorometers, these methods have become very useful in ecotoxicological studies. This review provides a summary of the research done over the last 10 years concerning the study, by using chlorophyll fluorescence, of the herbicide toxic effects. Although numerous parameters are available, it is striking to notice that the majority of the studies done in the recent years used only a limited number of parameters, thus restraining in some way the interpretation of the obtained results. Furthermore, the use of the maximal photosystem II quantum yield to evaluate toxic effect of herbicides is probably not the best parameter due to its relatively low sensitivity. One should take the advantage of using other parameters such as the operational PSII quantum yield and the non-photochemical quenching since they integrate the entire physiological state of the plant and therefore should be more sensitive. We also recommend the systematic determination of EC50 values in future studies since such determination will permit a more accurate comparison between published reports.
Selecting three adjacent vineyards as test objects, this paper studied the effects of applying herbicide in growth season on the leaf photosynthetic apparatus and branch nutrient storage of grape Kyoho (Vitis vinfrraxVitis labrusca). In the vineyards T1 and T2 where herbicide was applied in 2009, the net photosynthesis rate (Pa) of grape leaves had a significant decrease, as compared with that in vineyard CK where artificial weeding was implemented. The leaves at the fourth node in vineyard T1 and those at the sixth node in vineyard T2 had the largest decrement of Pn (40.5% and 32.1%, respectively). Herbicide had slight effects on the leaf stomatal conductance (Gs). In T1 where herbicide application was kept on with in 2010, the Pn, was still significantly lower than that in CK; while in T2 where artificial weeding was implemented in 2010, the Pn and Gs of top- and middle node leaves were slightly higher than those in T1, but the Pn was still lower than that in CK, showing the aftereffects of herbicide residual. The herbicide application in 2009 decreased the leaf maximum photochemical efficiency of PS II (Fv/Fm) and performance index (P1) while increased the relative variable fluorescence in the J step and K step, indicating the damage of electron transportation of PS II center and oxygen-evolving complex. Herbicide application decreased the pigment content of middle-node leaves in a dose-manner. Applying herbicide enhanced the leaf catalase and peroxidase activities significantly, increased the superoxide dismutase (SOD) activity of middle-node leaves, but decreased the SOD activity of top- and bottom node leaves. After treated with herbicide, the ascorbate peroxidase (APX) activity of middle- and bottom node leaves increased, but that of top-node leaves decreased. Herbicide treatment aggravated leaf lipid peroxidation, and reduced the soluble sugar, starch, free amino acids, and soluble protein storage in branches.
The herbicide Command (2-(2-chlorophenyl)methyl-4, 4-dimethyl-3-isoxazolidinone) does not affect the in vitro activities of the plastid enzymes catalyzing the steps leading from isopentenyl diphosphate to geranylgeranyl diphosphate and phytoene, i.e. the isopentenyl diphosphate isomerase, prenyl transferase and phytoene synthase. The extractable activities of these enzymes in herbicide-treated seedlings are also not affected. Nevertheless, the synthesis of chlorophylls and carotenoids in treated seedlings is severely inhibited in vivo. The mode of action of Command remains still unknown.
Enzymes of the 1-deoxy-D-xylulose 5-phosphate/2-C-methylerythritol 4-phosphate (DOXP/MEP) pathway are targets for new herbicides and antibacterial drugs. Until now, no inhibitors for the DOXP synthase have been known of. We show that one of the breakdown products of the herbicide clomazone affects the DOXP synthase. One inhibitor of the non-mevalonate pathway, fosmidomycin, blocks the DOXP reductoisomerase (DXR) of plants and bacteria. The I(50) values of plants are, however, higher than those found for the DXR of Escherichia coli. The DXR of plants, isolated from barley seedlings, shows a pH optimum of 8.1, which is typical for enzymes active in the chloroplast stroma.
Adaptation In saturating light radish seedlings grown in high-light growth conditions (90 W · m ⁻² ) possess a much higher photosynthetic capacity on a chlorophyll and leaf area basis than the low-light grown plants (10 W · m ⁻² ). The higher CO 2 -fixation rate of HL-plants is due to the presence of HL-chloroplasts which possess a different ultrastructure and also different levels of the individual chlorophyll-carotenoid-proteins than the LL-chloroplasts of LL-seedlings.
1. Ultrastructure: The high-light adapted chloroplasts are characterized by fewer photo synthetic membranes per chloroplast section, by low grana stacks (only few thylakoids per granum), a lower stacking degree of thylakoids, a higher proportion of non-appressed membranes (stroma thylakoids + end grana membranes) and a high starch content. The LL-chloroplasts possess no starch, their grana stacks are higher (up to 17 thylakoids per granum) and also significantly broader than that of HL-chloroplasts.
2. Chlorophyll-proteins: The photosynthetic apparatus of HL-chloroplasts contains a larger proportion of chlorophyll a-proteins of photosystem I (CPIa + CPI) and of photosystem II (CPa, the presumable reaction center of PS II) than the LL-chloroplasts which possess a higher proportion of light-harvesting chlorophyll a/b-proteins (LHCP 1 , LHCP 2 , LHCP 3 , LHCP y ). The higher levels of LHCPs in LL-plants are associated with a higher ground fluorescence fo and maximum fluorescence fp of the in vivo chlorophyll.
3. Chlorophyll and carotenoid ratios: The chloroplasts of HL-plants possess a higher proportion of chlorophyll a and β-carotene (higher values for the ratios chlorophyll a /b and lower values for a/c and x/c) which reflect the increased level of the chlorophyll a/β-carotene-proteins CPIa, CPI and CPa. The higher level of light-harvesting chlorophyll a/b-xanthophyll-proteins (LHCPs) in LL-plants is also indicated by an increased content of xanthophylls and chlorophyll b as seen from lower a/b and higher x/c and a/c ratios.
4. The results indicate that plants possess the capacity for an ontogenetic adaptation of their photosynthetic apparatus to the incident light intensity. The HL-chloroplasts of HL-plants which contain less antenna chlorophyll, are adapted for a more efficient photosynthetic quantum conversion at light saturation than the LL-chloroplasts with high grana stacks. The correlation between higher levels of light-harvesting chlorophyll a/b-proteins (LHCPs) and a higher stacking degree of thylakoids, and the involvement of LHCPs in stacking is discussed.
The uneven distribution of carotenoids and chlorophylls between several chlorophyll- carotenoid-proteins isolated from radish chloroplasts by SDS-polyacrylamide-gel electrophoresis is described.
Lutein and neoxanthin are enriched in the light-harvesting chlorophyll a/b-protein LHCP 3 , which exhibits low chlorophyll a/b ratios (1.1-1.3) and high values for the ratio chlorophyll a/β-carotene (a/c = 60-180).
β-carotene is bound not only to the chlorophyll a-protein CPI + CPIa of photosystem I, but also to the chlorophyll a-protein CPa. Both chlorophyll a-proteins are characterized by high values for the ratio a/b and low values for the ratio a/c.
The photosynthetic apparatus of plants responds to changing light quantity and quality with coordinated changes in both the light-harvesting antennae of the photosystems and the amounts of electron transport components and ATP synthase. These compositional modulations are accompanied by changes in thylakoid membrane organisation and photosynthetic capacity. It is now clear that there is a dynamic continuum of organisation and function of the photosynthetic apparatus from the appressed granal and non-appressed stroma thylakoids within a chloroplast, to different chloroplasts within a leaf, to leaves within and between species. While it is very unlikely that there is a unique solution to photosynthesis in the sun or shade, substantial changes in composition, and hence thylakoid membrane organisation and function, are elicited as part of sun/shade responses.
The photosynthetic CO2-fixation rates, chlorophyll content, chloroplast ultrastructure and other leaf characteristics (e.g. variable fluorescence, stomata density, soluble carbohydrate content) were studied in a comparative way in sun and shade leaves of beech (Fagus sylvatica) and in high-light and low-light seedlings. 1. Sun leaves of the beech possess a smaller leaf area, higher dry weight, lower water content, higher stomata density, higher chlorophyll a/b ratios and are thicker than the shade leaves. Sun leaves on the average contain more chlorophyll in a leaf area unit; the shade leaf exhibits more chlorophyll on a dry weight basis. Sun leaves show higher rates for dark respiration and a higher light saturation of photosynthetic CO2-fixation. Above 2000 lux they are more efficient in photosynthetic quantum conversion than the shade leaves. 2. The development of HL-radish plants proceeds much faster than that of LL-plants. The cotyledons of HL-plants show a higher dry weight, lower water content, a higher ratio of chlorophyll a/b and a higher gross photosynthesis rate than the cotyledons of the LL-plants, which possess a higher chlorophyll content per dry weight basis. The large area of the HL-cotyledon on the one hand, as well as the higher stomata density and the higher respiration rate in the LL-cotyledon on the other hand, are not in agreement with the characteristics of sun and shade leaves respectively. 3. The development, growth and wilting of wheat leaves and the appearance of the following leaves (leaf succession) is much faster at high quanta fluence rates than in weak light. The chlorophyll content is higher in the HL-leaf per unit leaf area and in the LL-leaf per g dry weight. There are no differences in the stomata density and leaf area between the HL- and LL-leaf. There are fewer differences between HL- and LL-leaves than in beech or radish leaves. 4. The chloroplast ultrastructure of shade-type chloroplasts (shade leaves, LL-leaves) is not only characterized by a much higher number of thylakoids per granum and a higher stacking degree of thylakoids, but also by broader grana than in sun-type chloroplasts (sun leaves, HL-leaves). The chloroplasts of sun leaves and of HL-leaves exhibit large starch grains. 5. Shade leaves and LL-leaves exhibit a higher maximum chlorophyll fluorescence and it takes more time for the fluorescence to decline to the steady state than in sun and HL-leaves. The variable fluorescence VF (ratio of fluorescence decrease to steady state fluorescence) is always higher in the sun and HL-leaf of the same physiological stage (maximum chlorophyll content of the leaf) than in the shade and LL-leaf. The fluorescence emission spectra of sun and HL-leaves show a higher proportion of chlorophyli fluorescence in the second emission maximum F2 than shade and LL-leaves. 6. The level of soluble carbohydrates (reducing sugars) is significantly higher in sun and HL-leaves than in shade and LL-leaves and even reflects changes in the amounts of the daily incident light. 7. Some but not all characteristics of mature sun and shade leaves are found in HL- and LL-leaves of seedlings. Leaf thickness, dry weight, chlorophyll content, soluble carbohydrate level, photosynthetic CO2-fixation, height and width of grana stacks and starch content, are good parameters to describe the differences between LL- and HL-leaves; with some reservations concerning age and physiological stage of leaf, a/b ratios, chlorophyll content per leaf area unit and the variable fluorescence are also suitable.
A newly developed fluorescence measuring system is employed for the recording of chlorophyll fluorescence induction kinetics (Kautsky-effect) and for the continuous determination of the photochemical and non-photochemical components of fluorescence quenching. The measuring system, which is based on a pulse modulation principle, selectively monitors the fluorescence yield of a weak measuring beam and is not affected even by extremely high intensities of actinic light. By repetitive application of short light pulses of saturating intensity, the fluorescence yield at complete suppression of photochemical quenching is repetitively recorded, allowing the determination of continuous plots of photochemical quenching and non-photochemical quenching. Such plots are compared with the time courses of variable fluorescence at different intensities of actinic illumination. The differences between the observed kinetics are discussed. It is shown that the modulation fluorometer, in combination with the application of saturating light pulses, provides essential information beyond that obtained with conventional chlorophyll fluorometers.
A relative decrease of the high temperature part (above 60°C) of the chlorophyll fluorescence temperature curve during 3 h to 10 h greening period of barley (Hordeum vulgare L.) leaves was found to be concomitant to a decrease of Chl alb ratio and to a gradual increase of LHCP/core ratio found by electrophoresis and the ratio of granal to total length of thylakoid membranes. It is suggested that the high temperature part of the fluorescence temperature curve depends inversely on the relative amount of LHC II in thylakoid membranes.
Dynamic acclimation of the photosynthetic apparatus in response to environmental cues, particularly light quantity and quality, is a widely-observed and important phenomenon which contributes to the tolerance of plants against stress and helps to maintain, as far as possible, optimal photosynthetic efficiency and resource utilization. This mini-review represents a scrutiny of a number of possible photoreceptors (including the two photosystems acting as light sensors) and signal transducers that may be involved in producing acclimation responses. We suggest that regulation by signal transduction may be effected at each of several possible points, and that there are multiple regulatory mechanisms for photosynthetic acclimation.
Synthese des mecanismes de photoprotection chez les vegetaux, en reponse a un eclairement energetique; implication des carotenoides, en particulier la zeaxanthine, a la dissipation d'energie, en relation avec le cycle des xanthophylles
Publisher Summary This chapter presents detailed information on chlorophylls and carotenoids to give practical directions toward their quantitative isolation and determination in extracts from leaves, chloroplasts, thylakoid particles, and pigment proteins. The chapter focuses on the spectral characteristics and absorption coefficients of chlorophylls, pheophytins, and carotenoids, which are the basis for establishing equations to quantitatively determine them. Therefore, the specific absorption coefficients of the pigments are re-evaluated. This is achieved by using a two-beam spectrophotometer of the new generation, which allows programmed automatic recording and printing out of the proper wavelengths and absorbancy values. Several procedures have been developed for the separation of the photosynthetic pigments, including column (CC), paper (PC), and thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC). All chloroplast carotenoids exhibit a typical absorption spectrum that is characterized by three absorption maxima (violaxanthin, neoxanthin) or two maxima with one shoulder (lutein and β-carotene) in the blue spectral region.
Chlorophyll fluorescence parameters (Chl FPs) derived from the slow (long-term) induction kinetics of modulated Chl a fluorescence are reviewed and analysed with respect to their application in photosynthesis research. Only four mutually independent Chl FPs, calculated from values of five essential Chl fluorescence (ChlF) yields, are distinguished as the basic ones. These are: the maximum quantum yield of PS2 photochemistry (P
O), the photochemical quenching of variable ChlF (qP), the non-photochemical quenching of variable ChlF (qN), and the relative change of minimum ChlF (qO). P
O refers to the dark-adapted state of a thylakoid membrane, qP, qN and qO characterise the light-adapted state. It is demonstrated that all other Chl FPs can be determined using this quartet of parameters. Moreover, three FPs related to the non-radiative energy dissipation within thylakoid membranes are evaluated, namely: the non-photochemical ChlF quenching (NPQ), the complete non-photochemical quenching of ChlF (qCN), and the effective quantum yield of non-photochemical processes in PS2 (N). New FPs, the total quenching of variable ChlF (qTV) and the absolute quenching of ChlF (qA) which allow to quantify co-action of the photochemical and non-photochemical processes during a light period are defined and analysed. The interpretation of Chl FPs and recommendations for their application in the photosynthesis research are also given. Some alternative FPs used in the laboratory practice have only an approximate character and can lead to incorrect conclusions if applied to stressed plants. They are reviewed and compared with the standard ones. All formulae and conclusions discussed herein are verified using experimental values obtained on young seedlings of the Norway spruce (Picea abies [L.] Karst.).
The ability of spring barley (Hordeum vulgare cv. Akcent) to adjust the composition and function of the photosynthetic apparatus to growth irradiances of 25–1200 μmol
m−2 s−1 was studied by gas exchange and chlorophyll a fluorescence measurements and high-performance liquid chromatography. The increased growth irradiance stimulated light- and
CO2-saturated rates of CO2 assimilation expressed on a leaf area basis up to 730 μmol m−2 s−1 (HL730), whereas at an irradiance of 1200 μmol m−2 s−1 (EHL1200) both rates decreased significantly. Further, the acclimation to EHL1200 was associated with an extremely high chlorophyll
a/b ratio (3.97), a more than doubled xanthophyll cycle pool (VAZ) and a six-fold higher de-epoxidation state of the xanthophyll
cycle pigments as compared to barley grown under 25 μmol m−2 s−1 (LL25). EHL1200 plants also exhibited a long-term inhibition of Photosystem II (PS II) photochemical efficiency (F
v/F
m). Photosynthetic capacity, chlorophyll a/b and VAZ revealed a linear trend of dependence on PS II excitation pressure in a certain range of growth irradiances (100–730
μmol m−2 s−1). The deviation from linearity of these relationships for EHL1200 barley is discussed. In addition, the role of increased
VAZ and/or accumulation of zeaxanthin and antheraxanthin in acclimation of barley to high irradiance is studied with respect
to regulation of non-radiative dissipation and/or photochemical efficiency within PS II.
Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity. Absorption of light that exceeds a plant's capacity for fixation of CO2 results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism. This regulatory process, termed nonphotochemical quenching, maintains the balance between dissipation and utilization of light energy to minimize generation of oxidizing molecules, thereby protecting the plant against photo-oxidative damage. To identify specific proteins that are involved in nonphotochemical quenching, we have isolated mutants of Arabidopsis thaliana that cannot dissipate excess absorbed light energy. Here we show that the gene encoding PsbS, an intrinsic chlorophyll-binding protein of photosystem II, is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis. These results indicate that PsbS may be the site for nonphotochemical quenching, a finding that has implications for the functional evolution of pigment-binding proteins.
Higher plants and several photosynthetic algae contain the plastidic 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol 4-phosphate pathway (DOXP/MEP pathway) for isoprenoid biosynthesis. The first four enzymes and their genes are known of this novel pathway. All of the ca. 10 enzymes of this isoprenoid pathway are potential targets for new classes of herbicides. Since the DOXP/MEP pathway also occurs in several pathogenic bacteria, such as Mycobacterium tuberculosis, and in the malaria parasite Plasmodium falciparum, all inhibitors and potential herbicides of the DOXP/MEP pathway in plants are also potential drugs against pathogenic bacteria and the malaria parasite. Plants with their easily to handle DOXP/MEP-pathway are thus very suitable test-systems also for new drugs against pathogenic bacteria and the malaria parasite as no particular security measures are required. In fact, the antibiotic herbicide fosmidomycin specifically inhibited not only the DOXP reductoisomerase in plants, but also that in bacteria and in the parasite P. falciparum, and cures malaria-infected mice. This is the first successful application of a herbicide of the novel isoprenoid pathway as a possible drug against malaria.
Here we describe the in vitro reconstitution of photosystem I light-harvesting complexes with pigments and proteins (Lhca1 and Lhca4) obtained by overexpression of tomato Lhca genes in Escherichia coli. Using Lhca1 and Lhca4 individually for reconstitution results in monomeric pigment-proteins, whereas a combination thereof yields a dimeric complex. Interactions of the apoproteins is highly specific, as reconstitution of either of the two constituent proteins in combination with a light-harvesting protein of photosystem II does not result in dimerization. The reconstituted Lhca1/4, but not complexes obtained with either Lhca1 or Lhca4 alone, closely resembles the native LHCI-730 dimer from tomato leaves with regard to spectroscopic properties, pigment composition, and stoichiometry. Monomeric complexes of Lhca1 or Lhca4 possess lower pigment/protein ratios, indicating that interactions of the two subunits not only facilitates pigment reorganization but also recruitment of additional pigments. In addition to higher averages of chlorophyll a/b ratios in monomeric complexes than in LHCI-730, comparative fluorescence and CD spectra demonstrate that heterodimerization involves preferential ligation of more chlorophyll b.
Enzymes of the 1-deoxy-D-xylulose 5-phosphate/2-C-methylerythritol 4-phosphate (DOXP/MEP) pathway are targets for new herbicides and antibacterial drugs. Until now, no inhibitors for the DOXP synthase have been known of. We show that one of the breakdown products of the herbicide clomazone affects the DOXP synthase. One inhibitor of the non-mevalonate pathway, fosmidomycin, blocks the DOXP reductoisomerase (DXR) of plants and bacteria. The I(50) values of plants are, however, higher than those found for the DXR of Escherichia coli. The DXR of plants, isolated from barley seedlings, shows a pH optimum of 8.1, which is typical for enzymes active in the chloroplast stroma.
The effect of FMC 57020 [2-(2-chlorophenyl) methyl-4,4-dimethyl-3-isoxalidinone] on chloroplast development was examined in the cotyledons of 5-day-old, etiolated pitted morningglory ( Ipomoea lacunosa L. ♯ IPOLA) seedlings grown from seeds inbibed for 24 h in water or 0.5 mM FMC 57020. In etiolated tissues, protochlorophyllide content was unaffected by FMC 57020; however, the herbicide eliminated carotenoid accumulation. There was no effect of FMC 57020 on phytoene or phytofluene content, although norflurazon [4-chloro-5-(methylamino)-2-(3-trifluoromethyl) phenyl)-3(2 H )-pyridazinone] increased phytoene content in these tissues. The Shibata shift was greatly retarded in FMC 57020-treated cotyledons, suggesting that phytol levels are also reduced by the herbicide. There were no ultrastructural effects on etioplasts; however, under low white light (150 μE·m ⁻² ·s ⁻¹ PAR), plastids of FMC 57020-treated seedlings did not develop into chloroplasts but rapidly developed ultrastructural symptoms of photobleaching. Starch was not mobilized in herbicide-treated plastids and sugar levels were higher in these plastids than in control plastids. Etiolated hypocotyl growth was inhibited by FMC 57020, whereas norflurazon had no effect upon it. Our results suggest that FMC 57020 blocks both diterpene and tetraterpene synthesis.
Changes in the photosynthetic light-response curve during leaf development were determined for the fourth leaf of maize crops sown on 23 April and 10 June. Temperatures were unusually mild during late spring/early summer and neither crop experienced chilling damage. The concept of thermal time was used to take into account the effects of different temperature regimes on developmental stage, thereby enabling photosynthetic light-response data to be combined for both crops to describe the general response. Large variations in the upper asymptote (Asat) and convexity (Θ) of the light-response curve occurred during leaf development, but the maximum quantum yield of CO2 assimilation remained relatively constant throughout. Dark respiration rates showed a small but significant decrease with leaf age and generally ranged between 5 and 10% of Asat. A simple mathematical model was developed to assess the sensitivity of daily leaf photosynthesis (AL) to reductions in the Asat, Θ and the initial slope (Φ) of the light-response curve at different stages of leaf development. On bright sunny days, and at all developmental stages, AL was ca. twice as sensitive to reductions in Asat than to reductions in Φ and Θ. In overcast conditions, however, all three parameters contributed significantly to reductions in leaf photosynthesis, although the contribution of Φ was greatest during early leaf growth, while older leaves were most sensitive to depressions in Asat. The implications of these results for modelling the sensitivity of canopy photosynthesis to chill-induced photoinhibition of the light-response curve are discussed.
A series of experiments is presented investigating short term and long term changes of the nature of the response of rate of CO2 assimilation to intercellular p(CO2). The relationships between CO2 assimilation rate and biochemical components of leaf photosynthesis, such as ribulose-bisphosphate (RuP2) carboxylase-oxygenase activity and electron transport capacity are examined and related to current theory of CO2 assimilation in leaves of C3 species. It was found that the response of the rate of CO2 assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at low and high intercellular p(CO2). In longer term changes in CO2 assimilation rate, induced by different growth conditions, the initial slope of the response of CO2 assimilation rate to intercellular p(CO2) could be correlated to in vitro measurements of RuP2 carboxylase activity. Also, CO2 assimilation rate at high p(CO2) could be correlated to in vitro measurements of electron transport rate. These results are consistent with the hypothesis that CO2 assimilation rate is limited by the RuP2 saturated rate of the RuP2 carboxylase-oxygenase at low intercellular p(CO2) and by the rate allowed by RuP2 regeneration capacity at high intercellular p(CO2).
During the greening of etiolated barley seedlings the accumulation of chlorophylls and carotenoids wasdetermined in primary leaves together with the chlorophyll fluorescence ratio F690/F735 (at maximum and steady-state fluorescence) as well as the variable fluorescence decrease ratio (Rfd-values in 690 nm and 735 nm) as calculated from the fluorescence induction kinetics recorded by the LITWaF fluorometer. The variable chlorophyll fluorescence parameters (Fv/Fm, Fv/Fo, ΔF/Fm') were monitored using the pulse amplitude modulation chlorophyll fluorometer PAM, and photosynthetic net CO2 fixation by using a CO2/H2O porometer. All parameters were used to characterize the development of photosynthetic activity under illumination with continuous white light in the upper (oldest), middle and lower (youngest) part of the primary leaf blade of etiolated barley seedlings. The time course of changes in the studied parameters provided information on the gradual and age-dependent development of photosynthetic activity in the three leaf parts of different age. During the greening process the chlorophyll fluorescence ratio F690/F735 at maximum and steady-state fluorescence, fm and fs, strongly correlated with the total chlorophyll content (in an inverse curvilinear relationship) in the upper, middle and lower part of etiolated leaves. Though the absolute values were different, there also existed a linear correlation between the Rfd-values measured at 690 nm and 735 nm.
Photosynthesis and growth were studied in tobacco (Nicotiana tabacum L.) plants exhibiting gradually reduced chlorophyll levels as a result of a glutamate 1-semialdehyde aminotransferase antisense transformation. Measurements of leaf pigmentation, spectral absorptance, chlorophyll fluorescence, CO2 gas exchange, and leaf area growth were carried out on leaves with an equal state of leaf and plant ontogeny, i.e., the 8th to 12th leaf from the top of plants with a total of 22 to 26 leaves. The combination of different growth light intensities (300 and 30 μmol · m-2 · s-1) and of differences in chlorophyll accumulation resulted in photon absorption rates of the leaves differing by a factor of 31. As a result of the gradually reduced energy input, rates of electron transport, net CO2 assimilation, and growth were lowered. However, the extent of this reduction varied between the hierarchic process levels: In relation to leaves of the experimental variant with the highest energy input, leaves with 10 % of the rates of photon absorption and electron transport reached 13 % of the assimilation rate and 53 % of the maximum leaf area growth rate. The data show that the electron transport rate was adjusted to a level slightly in excess of the energy demand of carbon assimilation, and the rate of net CO2 uptake was in excess of the carbohydrate demand of leaf area growth. The effort of these excessive flows of energy and carbon is the increased stability of the system under conditions of varying resource availability. As a result of excessive flows, differences in energy input restriction are compensated to a certain extent at higher hierarchic levels in leaves. Regarding the whole plant, another compensating mechanism plays a role: The differences between the variants were further diminished, as plants growing under severe energy input limitation reached total leaf areas equal to those of control plants with a delay of 40 days.
The effect of chlorophyll concentration, light intensity and leaf temperature on the chlorophyll fluorescence ratio F685/F730 of intact leaves was evaluated. Fluorescence reabsorption that affects mainly the F685 band increases with chlorophyll concentration. This phenomenon was studied on an aurea mutant of tomato and its wild type, with very different chlorophyll content. Fluorescence spectra of the two genotypes were corrected for reabsorption using their transmittance and reflectance properties. The correction removes most of the differences in the two fluorescence spectra. The F685/F730 decreases during the declining phase of the fluorescence induction kinetics. We demonstrated that when red light is used to induce the fluorescence kinetics the variation of F685/F730 is not due to a change in the leaf absorption, as proved by the simultaneous measurement of leaf transmittance. This evidence suggests that the F685/F730 ratio is sensitive to changes in the photosynthetic activity of the leaf. Under natural conditions, the F685/F730 ratio markedly decreases as light intensity and leaf temperature increase during a daily cycle. This behaviour can be due to photoinhibitory and heat stresses. In controlled laboratory conditions, the F685/F730 ratio was seen to decrease under high light intensity (> 1000 μmol m⁻² s⁻¹) at constant leaf temperature. It decreases also when leaf temperature was decreased from 25°C to 14°C at low light intensity (150 μmol m⁻² s⁻¹). A possible interpretation of these experimental data relies on a non-negligible contribution of PSI to the total fluorescence at physiological temperatures with respect to - PSII fluorescence. Changes in the photosynthetic activity of the two photosystems may induce variation in the F685/F730 ratio. Our results indicate that light intensity and leaf temperature are important parameters to take into account when the F685/F730 ratio is used as stress indicator.
We recently discussed a method for measuring optical properties of light scattering and absorbing plant tissue (Seyfried, Fukshansky & Schafer, 1983). This method has been used to measure the changes in optical properties of cotyledons between 360 and 1000 run during the first 7d of development. The seedlings were either etiolated or grown under continuous white light, the latter either herbicide-treated (SAN 9789 = Norflurazon) or untreated. Some of the observed changes in seedlings grown under white light are due to chlorophyll accumulation. This accumulation leads to an increase in absorption coefficients at all wavelengths except in the 750 to 850 nm region. Reflectance, transmittance, and the scattering coefficient decreased markedly. Other changes seem to be independent of light conditions since they occur in much the same way under all treatments. These are a generally decreasing reflectance and scattering coefficient and an even stronger decrease of reflectance from the upper face of the cotyledon as compared to the reflectance from the lower face, in particular in the blue region of the spectrum. The observed changes are discussed in terms of light gradients and the resulting problems for in vivo spectroscopy.
Photosystem II plays a central role not only in energy transduction, but also in monitoring the molecular redox mechanisms involved in signal transduction for acclimation to environmental stresses. Central to the regulation of photosystem II (PSII) function as a light-driven molecular machine in higher plant leaves, is an inevitable photo-inactivation of one PSII after 106–107 photons have been delivered to the leaf, although the act of photoinactivation per se requires only one photon. PSII function in acclimated pea leaves shows a reciprocity between irradiance and the time of illumination, demonstrating that the photoinactivation of PSII is a light dosage effect, depending on the number of photons absorbed rather than the rate of photon absorption. Hence, PSII photoinactivation will occur at low as well as high irradiance. There is a heterogeneity of PSII functional stability, possibly with less stable PSII monomers being located in grana margins and more stable PSII dimers in appressed granal domains. Matching the inevitable photoinactivation of PSII, green plants have an intrinsic capacity for D1 protein synthesis to restore PSII function which is saturated at very low light. Photoinhibition of PSII in vivo is often a photoprotective strategy rather than a damaging process.
Based on the analysis of fluorescence quenching, the nonphotochemical dissipative processes were investigated in Norway spruce
needles during acclimation to winter and spring conditions. The maximum nonphotochemical fluorescence quenching (qNmax) was reached at lower irradiances in winter (up to 310 µmol m-2 s-1) than in spring (about 1130 µmol m-2 s-1), but its values
were nearly the same (qNmax = 0.91±0.01) during both winter and spring measurements. In early winter the pronounced initial fluorescence quenching (q0)
suggested that nonradiative energy dissipation in the antennae complexes dominated. Significantly lower q0 (by 40-60 % compared
to winter needles) during acclimation of needles to spring conditions supported a significant contribution of quenching in
the reaction centres. These findings support the hypothesis that the antennae systems and reaction centres cooperate in the
protective dissipation of excess excitation energy.
Barley seedlings (Hordeum vulgare L. cv. Boone) were grown at 20C with a 16h/8h light/dark cycle of either high (H) intensity (550 mole m-2 s-1) or low (L) intensity (55 mole m-2 s-1) white light. Plants were transferred from high to low (H L) or low to high (L H) light intensity at various times from 4 to 8 d after leaf emergence from the soil. Primary leaves were harvested at the beginning of the photoperiod and a 3 cm apical segment removed for analysis. H control plants had greater chlorophyll (Chl) per leaf area and higher Chl a/b ratios than L controls. Analysis of Chl-protein complexes revealed that H and L plants had the same percentage of total Chl (62–65%) associated with Photosystem II (PS II), but that the organization of Chl within PS II was different. H plants contained lower levels of light-harvesting complex (LHC-II) and higher levels of the PS II complex CPa compared with L plants. Leaf Chl content and Chl organization within PS II were sensitive to changes in light intensity. In H L plants, leaf Chl content decreased, Chl a/b ratio decreased, and a redistribution of Chl from CPa to LHC-II occurred during acclimation to low light. Acclimation of L H plants to high light involved an increase in leaf Chl content, an increase in Chl a/b ratio, and a decrease in LHC-II. In contrast, the level of photosystem I related Chl-protein complexes (CP1 + CP1a) was similar in all light treatments. The light acclimation process occurred slowly over a period of 6 to 8 d in H L and L H plants.
The role of the xanthophyll cycle in regulating the energy flow to the PS II reaction centers and therefore in photoprotection was studied by measurements of light-induced absorbance changes, Chl fluorescence, and photosynthetic O2 evolution in sun and shade leaves of Hedera canariensis. The light-induced absorbance change at 510 nm (A510) was used for continuous monitoring of zeaxanthin formation by de-epoxidation of violaxanthin. Non-radiative energy dissipation (NRD) was estimated from non-photochemical fluorescence quenching (NPQ).High capacity for zeaxanthin formation in sun leaves was accompanied by large NRD in the pigment bed at high PFDs as indicated by a very strong NPQ both when all PS II centers are closed (F'm) and when all centers are open (F'o). Such Fo quenching, although present, was less pronounced in shade leaves which have a much smaller xanthophyll cycle pool.Dithiothreitol (DTT) provided through the cut petiole completely blocked zeaxanthin formation. DTT had no detectable effect on photosynthetic O2 evolution or the photochemical yield of PS II in the short term but fully inhibited the quenching of Fo and 75% of the quenching of Fm, indicating that NRD in the antenna was largely blocked. This inhibition of quenching was accompanied by an increased closure of the PS II reaction centers.In the presence of DTT a photoinhibitory treatment at a PFD of 200 mol m-2 s-1, followed by a 45 min recovery period at a low PFD, caused a 35% decrease in the photon yield of O2 evolution, compared to a decrease of less than 5% in the absence of DTT. The Fv/Fm ratio, measured in darkness showed a much greater decrease in the presence than in the absence of DTT. In the presence of DTT Fo rose by 15–20% whereas no change was detected in control leaves.The results support the conclusion that the xanthophyll cycle has a central role in regulating the energy flow to the PS II reaction centers and also provide direct evidence that zeaxanthin protects against photoinhibitory injury to the photosynthetic system.
Barley seedlings (Hordeum vulgare L. Boone) were grown at 20C with 16 h/8 h light/dark cycle of either high (H) intensity (500 mole m-2 s-1) or low (L) intensity (55 mole m-2 s-1) white light. Plants were transferred from high to low (H L) and low to high (L H) light intensity at various times from 4 to 8 d after leaf emergence from the soil. Primary leaves were harvested at the beginning of the photoperiod. Thylakoid membranes were isolated from 3 cm apical segments and assayed for photosynthetic electron transport, Photosystem II (PS II) atrazine-binding sites (QB), cytochrome f(Cytf) and the P-700 reaction center of Photosystem I (PS I). Whole chain, PS I and PS II electron transport activities were higher in H than in L controls. QB and Cytf were elevated in H plants compared with L plants. The acclimation of H L plants to low light occurred slowly over a period of 7 days and resulted in decreased whole chain and PS II electron transport with variable effects on PS I activity. The decrease in electron transport of H L plants was associated with a decrease in both QB and Cytf. In L H plants, acclimation to high light occurred slowly over a period of 7 days with increased whole chain, PS I and PS II activities. The increase in L H electron transport was associated with increased levels of QB and Cytf. In contrast to the light intensity effects on QB levels, the P-700 content was similar in both control and transferred plants. Therefore, PS II/PS I ratios were dependent on light environment.
The red laser-induced chlorophyll-fluorescence induction kinetics of predarkened leaf samples were registered simultaneously in the 690 and 730 nm regions i.e., in the region of the two chlorophyll fluorescence emission maxima. From the induction kinetics the chlorophyll fluorescence ratio F690/F730 was calculated. The ratio F690/F730 shows to be dependent on the chlorophyll content of leaves. It is significantly higher in needles of damaged spruces (values of 0.45–0.9) than in normal green needles of healthy trees (values of 0.35–0.5). During development and greening of maple leaves the ratio F690/F730 decreases with increasing chlorophyll content. Determination of the ratio F690/F730 can be a suitable method of monitoring changes in chlorophyll content in a non-destructive way in the same leaves during development or the yellowish-green discolouration of needles of damaged spruces in the Black Forest with the typical tree decline symptoms.
A theoretical model is presented describing the distortion of chlorophyll fluorescence spectra of a chloroplast or a group of chloroplasts by the effect of fluorescence reabsorption. Model calculations using the experimental data show that the primary reabsorption effect occurs already within one chloroplast and the spectral distortion depends significantly on the excitation regime of the chloroplast. A theoretical dependence of the distortion function, defined as a change in the F(685)/F(735) fluorescence band ratio, on the mean chlorophyll concentration in a chloroplast is predicted for different light excitation regimes. The distortion of measured chlorophyll fluorescence spectra at 77 K of chloroplast suspension adsorbed on filter papers of two strongly different diffusive reflectivities and at different mean chlorophyll concentrations are discussed with the help of the presented theory.
The herbicidal action of dimethazone [FMC 57020; 2-(2-chlorophenyl) methyl-4,4-dimethyl-3-isoxalidinone] on cowpea (Vigna unguiculata L.) primary leaves was studied. Seeds were imbibed in 0.5 mM herbicide for 1 day and then seedlings were grown in darkness. In 6-day-old, etiolated seedlings, there was no effect of the herbicide on protochlorophyllide accumulation or on phototransformation of protochlorophyllide to chlorophyllide, however, the Shibata shift was greatly slowed. Accompanying this was a delay in phytylation of chlorophyllide. Protochlorophyllide resynthesis in a dark period after phototransformation of existing protochlorophyllide in etiolated tissue was also slowed by dimethazone. In the light, carotenoid accumulation and chlorophyll accumulation were slowed by the herbicide, resulting a pale green appearance of the leaves. The capacity for CO2-dependent oxygen evolution or FeCN-dependent oxygen evolution did not develop in dimethazone-treated tissue during 24 hr of light exposure. In situ measurement of variable fluorescence and cytochrome f photooxidation/dark reduction indicated that some cyclic electron transport developed very slowly in dimethazone-treated plants. No effect of the herbicide was found on either FeCN-dependent oxygen evolution or variable fluorescence in fully greened tissues. Dimethazone was concluded to have an effect on chloroplast development rather than a direct effect on photosynthesis.
The development of light harvesting complexes (LHCs) of both photosystems in the course of greening of barley leaves was investigated using the following three typical changes in 77 K chlorophyll a (Chl a) fluorescence spectra: (i) shift of PS I emission maximum to 741–743 nm together with its substantial increase: (ii) relative increase of Chl b excitation maximum in the Soret region; (iii) shift of the red Chl a excitation maximum from 677 to 680 nm. Moreover, a pronounced long-wavelength excitation maximum of Chl a, E698, appeared in the red region of 77 K excitation spectrum for photosystem (PS) I emission after 32 h of greening. The rise of E698, which was observed for the first time as a main excitation maximum in the red region of the excitation spectrum for fully green barley leaves, is related to an increasing efficiency of energy transfer from LHCs to Chl a forms fluorescing both at 685 nm and 743 nm. For broken chloroplasts isolated from mature barley leaves the E698 band disappeared almost completely from the excitation spectrum and a pronounced decrease of the efficiency of energy transfer from Chl b to fluorescing Chl a occurred both within PS II and PS I. These findings support the relation between the appearance of E698 in the excitation spectrum of Chl a fluorescence originating from LHC I and a high functional integrity of LHCs.
The effects of dimethazone [FMC 57020; 2-(2-chlorophenyl)methyl-4,4-dimethyl-3-isoxalidinone] on the growth and ultrastructure of cowpea (Vigna unguiculata L.) were examined. Seeds were imbibed in 0.5 mM dimethazone for 1 day and grown for 4 to 5 subsequent days in darkness without the herbicide. The herbicide stunted etiolated hypocotyl growth and retarded greening under 150 μmol · m−2 · sec−1 white light. No effects of dimethazone on the in vivo absorption spectrum of the etiolated primary leaf was detected. The herbicide caused some reduction and disorganization of prothylakoids in etiplasts. After 3 hr of white light chlorophyll accumulation was greatly reduced in treated leaves and ultrastructural development of the chloroplasts of herbicide-treated tissues appeared to be retarded. Pronounced thylakoid disruption was noticed in some cells after 12 hr, was more common after 24 hr, and was found in all cells by 72 hr. Maximally affected plastids lacked thylakoids, had irregular envelopes, and contained numerous vesicles.
The sequential appearance of chlorophyll-protein complexes (CP) in greening barley leaves was studied by an improved method of SDS-polyacrylamide gel electrophoresis (PAGE). Solubilized thylakoid membranes were purified using a sucrose step gradient and CPs were separated by PAGE with low concentrations of SDS in solubilizing and reservoir buffers. At 10 min after the onset of illumination, a chlorophyll-protein complex (CPX) was detected. It was a labile CP, its chlorophyll (Chl) being easily released from the apoprotein during electrophoresis. The P700-chlorophyll a / b -protein complex (CPl) appeared after 45–60 min of illumination together with P700 activity. Light-harvesting chlorophyll a/b -protein complex (LHCP) began to accumulate at 2.5 h with the beginning of Chl b synthesis. In some cases a small amount of CPa could be detected after 6 h of greening. The time-difference spectrum between homogenates of leaves illuminated for 30 and 60 min had an absorbance maximum at 677 nm, showing that a red shift indicative of CPl formation began soon after completion of the Shibata shift. The time-difference spectrum between 3.5-h and 4.0-h illuminated leaves resembled the absolute spectrum of fully greened leaves, indicating that at this stage, spectral components were being synthesized at the same ratio at which they exist in fully greened tissues. Both absolute and time-difference spectral data supported the SDS-PAGE results.
The rectangular hyperbola is shown to be a poor description of the response of photosynthesis to irradiance for leaves of
a winter wheat crop. A model is derived which combines a simplified description of the biochemical reactions occurring within
the chloroplast with the physical diffusion of CO2 from the atmosphere. The model is a non-rectangular hyperbola and uses four parameters: Pnmax (maximum rate of net photosynthesis), Rd (rate of dark respiration), α (photochemical efficiency of photosynthesis at low light), and θ (ratio of physical to total
resistance to diffusion of CO2). The model is shown to be a significant improvement on the rectangular hyperbola. It provides
good fits both to our own measurements and to some data from the literature, and gives consistent and reliable estimates of
the four parameters.
The quenching action of dibromothymoquinone on fluorescence and on primary photochemistry was examined in chloroplasts at minus 196 degrees C. Both the initial (F0) and final (FM) levels of fluorescence as well as the fluorescence of variable yield (FV equals FM minus FO) were quenched at minus 196 degrees C to a degree which depended on the concentration of dibromothymoquinone added prior to freezing. The initial rate of photoreduction of C-550 at minus 196 degrees C, which was assumed to be proportional to maximum yield for primary photochemistry, phipo, was also decreased in the presence of dibromothymoquinone. Simple theory predicts that the ratio FV/FM should equal phipo. Excellent agreement was found in a comparison of relative values of phipo with relative values of FV/FM at various degrees of quenching by dibromothymoquinone. These results are taken to indicate that FO and FV are the same type of fluorescence, both emanating from the bulk chlorophyll of Photosystem II. Dibromothymoquinone appears to create quenching centers in the bulk chlorophyll of Photosystem II which compete with the reaction centers for excitation energy. The rate constant for the quenching of excitation energy by dibromothymoquinone is directly proportional to the concentration of the quencher. Rate constants for the de-excitation of excited chlorophyll molecules by fluorescence, kF, by nonradiative decay processes, kD, by photochemistry, kP, and by the specific quenching of dibromothymoquinone, kQ, were calculated assuming the absolute yield of fluorescence at FO to be either 0.02 or 0.05.
In vivo chlorophyll fluorescence measurements have become a valuable tool in ecophysiology. Fluorescence emission spectra are influenced by the reabsorption of the tissue and indicate the composition of the antenna system and are influenced by the chlorophyll content per leaf area. The fluorescence induction kinetics ("Kautsky effect") can be used to study photosynthetic activity. These rapid, non-destructive methods can be applied for ecophysiological field research to check the vitality of plants and to document stress effects on the photosynthetic apparatus. The Rfd-values (Rfd = fd/fs), the ratio of the fluorescence decrease (fd) to the steady state fluorescence (fs), can be taken as a rapid vitality index of the leaves and trees. We here describe fundamental chlorophyll fluorescence results of leaves which are needed for the interpretation of in vivo fluorescence signatures in stress physiology and in the forest dieback research.
Two plant test systems are presented in the search for new inhibitors of the non-mevalonate isoprenoid pathway. A derivative of clomazone appears to be an inhibitor of the deoxyxylulose 5-phosphate/methylerythritol 4-phosphate (DOXP/MEP) pathway of isoprenoid formation.
The capacity for photosynthetic acclimation in Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta was assessed during growth over a broad range of irradiance. Discontinuities in the response to growth irradiance were revealed for the light- and CO2-saturated rate of photosynthesis (P
max) and the ratio of chlorophyll a to chlorophyll b (Chl a/b). Three separate phases in the response of P
max and Chl a/b to growth light were evident, with increases at low and high irradiance ranges and a plateau at intermediate irradiance. By measuring all chlorophyll-containing components of the thylakoid membrane that contribute to Chl a/b we reveal that distinct strategies for growth at low and high irradiance underlie the discontinuous response. These strategies include, in addition to changes in the major light-harvesting complexes of photosystem II (LHCII), large shifts in the amounts of both reaction centres as well as significant changes in the levels of minor LHCII and LHCI components.
Photosystem I (PSI) holocomplexes were fractionated to study the organization of the light-harvesting complex I (LHC I) pigment-proteins in barley (Hordeum vulgare) plastids. LHC Ia and LHC Ib can be isolated as oligomeric, presumably trimeric, pigment-protein complexes. The LHC Ia oligomeric complex contains both the 24- and the 21.5-kD apoproteins encoded by the Lhca3 and Lhca2 genes and is slightly larger than the oligomeric LHC Ib complex containing the Lhca1 and Lhca4 gene products of 21 and 20 kD. The synthesis and assembly of LHC I during light-driven development of intermittent light-grown plants occurs rapidly upon exposure to continuous illumination. Complete PSI complexes are detected by nondenaturing Deriphat (disodium N-dodecyl-[beta]-iminodipropionate-160)-PAGE after 2 h of illumination, and their appearance correlates with that of the 730- to 740-nm emission characteristic of assembled LHC I. However, the majority of the newly synthesized LHC I apoproteins are present as monomeric complexes in the thylakoids during the early hours of greening. We propose that during development of the protochloroplast the LHC I apoproteins are first assembled into monomeric pigmented complexes that then aggregate into trimers before becoming attached to the pre-existing core complex to form a complete PSI holocomplex.
Using 77 K chlorophyll a (Chl a) fluorescence spectra in vivo, the development was studied of Photosystems II (PS II) and I (PS I) during greening of barley under intermittent light followed by continuous light at low (LI, 50 mumol m(-2) s(-1)) and high (HI, 1000 mumol m(-2) s(-1)) irradiances. The greening at HI intermittent light was accompanied with significantly reduced fluorescence intensity from Chl b excitation for both PS II (F685) and PS I (F743), in comparison with LI plants, indicating that assembly of light-harvesting complexes (LHC) of both photosystems was affected to a similar degree. During greening at continuous HI, a slower increase of emission from Chl b excitation in PS II as compared with PS I was observed, indicating a preferred reduction in the accumulation of LHC II. The following characteristics of 77 K Chl a fluorescence spectra documented the photoprotective function of an elevated content of carotenoids in HI leaves: (1) a pronounced suppression of Soret region of excitation spectra (410-450 nm) in comparison with the red region (670-690 nm) during the early stage of greening indicated a strongly reduced excitation energy transfer from carotenoids to the Chl a fluorescing forms within PS I and PS II; (2) changes in the shape of the excitation band of Chl b and carotenoids (460-490 nm) during greening under continuous light confirmed that the energy transfer from carotenoids to Chl a within PS II remained lower as compared with the LI plants.