No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The effect of UV-B and UV-C radiation on Hibiscus leaves determined by ultraweak luminescence and Fluorescence induction
Abstract
The effects of UV-C (254 nm) and UV-B (280-320 nm) on chlorophyll fluorescence induction and ultraweak luminescence (UL) in detached leaves of Hibiscus rosa-sinensis L. were investigated. UL from leaves exposed to UV-B and UV-C radiation reached a maximum 72 h after irradiation. In both cases most of the light was of a wavelength over 600 nm. An increase in the percentage of long wavelength light with time was detected. UV radiation increased peroxidase activity, which also reached a maximum 72 h after irradiation. UV-B and UV-C both reduced variable chlorophyll fluorescence. No effect on the amount of chlorophyll or UV screening pigments was observed with the short-term irradiation used in this investigation.
... The study also showed an increase in leaf peroxidase activity under the combination of white light and UV-B [140]. The increased peroxidase activity and ultraweak luminescence upon UV-B exposure and ascorbic acid incubated leaves represents a strong correlation in Hibiscus leaves [141] and sugar beet [140]. In a recent study, the most widely cultivated Iranian sugar beet variety, BR1, was used to analyze biochemical and physiological responses against different doses (3.042, 6.084, and 9.126 kJm −2 d −1 ) of UV-B radiation [142]. ...
Cultivated beets (sugar beets, fodder beets, leaf beets, and garden beets) belonging to the species Beta vulgaris L. are important sources for many products such as sugar, bioethanol, animal feed, human nutrition, pulp residue, pectin extract, and molasses. Beta maritima L. (sea beet or wild beet) is a halophytic wild ancestor of all cultivated beets. With a requirement of less water and having shorter growth period than sugarcane, cultivated beets are preferentially spreading from temperate regions to subtropical countries. The beet cultivars display tolerance to several abiotic stresses such as salt, drought, cold, heat, and heavy metals. However, many environmental factors adversely influence growth, yield, and quality of beets. Hence, selection of stress-tolerant beet varieties and knowledge on the response mechanisms of beet cultivars to different abiotic stress factors are most required. The present review discusses morpho-physiological, biochemical, and molecular responses of cultivated beets (B. vulgaris L.) to different abiotic stresses including alkaline, cold, heat, heavy metals, and UV radiation. Additionally, we describe the beet genes reported for their involvement in response to these stress conditions.
... Peroxidase activity increases substantially in Arabidopsis following UV exposure [35]. Increased peroxidase activity in response to supplemental UV-B radiation is observed in detached Hibiscus leaves [36] and Beta vulgaris [37]. Exposure of plant tissue to UV-B results in enhancement of production of oxyradicals and activates the plant antioxidant defence system against oxyradicals [38,39]. ...
https://meddocsonline.org/journal-of-plant-biology-and-crop-research/impact-of-exclusion-of-solar-UV-on-growth-performance-index-of-photosystem-II-and-leghemoglobin-content-of-soybean-var-JS-335.pdf
... Light stress is one of the most common sources of oxidative stress in plants (Dat et al., 2000). It has been reported that UV-B (280-315 nm) radiation can induce oxidative stress (Panagopoulos et al., 1989), however, the detail mechanism of ROS formation is yet unknown. The damaging effects of UV-B radiation includes conformational changes in nucleic acids, proteins, membranes, alterations in transpiration and photosynthesis, changes in growth, development, morphology, and ultimately yield in the plants (Singh et al., 2011). ...
The natural environment for mangrove plants is composed of a complex set of abiotic and biotic stress factors that include salinity, heavy metal, low oxygen, flooding, UV-B, water logging, and biotic interferences of various magnitude. Salinity stress exerts adverse effects on plants by disrupting the ionic and osmotic equilibrium of the cells leading to decrease in plant growth and development. Similarly, presence of heavy metals in environment induces a disturbance of the cellular redox balance, thereby affecting growth and productivity of mangrove plants. Anaerobic environment in mangroves manifested by anoxic or hypoxic condition exhibit various metabolic changes in plants to overcome the stress condition. Besides, the mangrove plants are also permanently exposed to various biotic stress factors that include microbial pathogens (viruses, bacteria and fungi), nematodes, insects etc. More often, these stress factors result in the production of reactive oxygen species (ROS) within different cellular compartments of the plant cell that are detrimental to the survival of the plants. However, the mangrove plants can withstand these stress conditions through morphological and physiological adaptations and development of an efficient antioxidative defence system composed of non-enzymatic and enzymatic systems. The antioxidant system works in concert to control the cascades of uncontrolled oxidation and protect plant cells from oxidative damage by scavenging of ROS produced owing to different abiotic and biotic stresses. The present review highlights various abiotic and biotic stress conditions that are prevalent in mangrove environment and the manner in which mangrove plants overcome these stress situations through metabolic changes and induction of antioxidant defence system.
... In addition, UV-B is suspected to cause cataracts, affect the human immune system and to be responsible for other health effects in humans and animals (Noonan and de Fabo 1990; De Fabo et al. 1990; Longstreth et al. 1998). Other concerns about adverse UV-B effects focus on reduced productivity, decreased food quality and other changes in terrestrial plants, with respect to both wild and crop plants (Panagopoulos et al. 1989; Björn 1989; Bornman 1991; Caldwell et al. 1998 ). Solar UV radiation impairs photosynthesis (Strid et al. 1990; Renger et Communicated Helgol Mar Res (2001) 55:35–44 DOI 10.1007/s101520000059 O R I G I N A L A RT I C L E al. 1991), stomatal movement (Negash 1987; Negash et al. 1987), and the growth and development of a large percentage of plants investigated so far (Teramura et al. 1990aTeramura et al. , 1990b Cen and Bornman 1990). ...
The European light dosimeter network of over 40 stations has been established in Europe and other continents equipped with
three-channel filter dosimeters to measure solar radiation in three channels, UV-B (280–315nm), UV-A (315–400nm) and photosynthetically
active radiation (PAR). The recorded data have been evaluated, and the monthly doses in all three channels show a strong latitudinal
dependence from northern Sweden to the Canary Islands. There are a few remarkable exceptions such as the data recorded at
the high mountain station on the Zugspitze (German Alps) and unequal doses at stations at comparable latitudes which indicate
the impact of local weather conditions and mean sunshine hours. While generally peak values are recorded in the months of
June and July, the UV-B maxima are shifted later into the year, which is due to the antagonistic functions of decreasing solar
angles and increasing transparency of the atmosphere as the total column ozone decreases in the second half of the year for
the Northern Hemisphere. This is supported by comparison with modelled total column ozone and satellite-based measurements.
Also the ratios of UV-B:UV-A and UV-B:PAR as well as UV-A:PAR peak during the summer months, with the exception of the northernmost
station at Abisko (north Sweden) where the UV-A:PAR ratio peaks in the winter months which is due to the specific photoclimatic
conditions north of the polar circle. The penetration of solar radiation into the water column was found to strongly depend
on the transparency of the water column. In Gran Canaria more than 10% of the surface UV-B penetrated to 4–5m depth. The
path of the solar eclipse on 11 August 1999 could be followed in several stations with different degrees of occlusion of the
sun disk.
Plants use antioxidant enzymes to remove reactive oxygen species (ROS) in cells directly or indirectly, thus ensuring normal metabolic reactions, which is a major mechanism to ameliorate the toxic effect of ROS generated by UV-B stress. The key factor for UV-B tolerance may be considered as UV-B-absorbing pigments, regulation of active oxygen species levels and activity of antioxidants, and the effective repair mechanism for PSII, one of the important components of photosynthetic electron transport chain. This chapter discusses the oxidative stress and antioxidative defence system in plants in response to UV-B stress. In response to the damaging effects of UV radiation, plants have developed defence mechanisms against UV-B, while allowing photosynthetically active radiation (PAR) to penetrate through the outer cell layers to support photosynthesis in the mesophyll and palisade tissues. Efficient antioxidant defence systems, including antioxidants and enzymes, have developed in plants to counteract the toxicity of ROS.
In olive (Olea europaea L.), hair removal had no effect on the photosynthetic rate and the apparent leaf resistance to water vapour diffusion in leaves illuminated with white light (900 μmol m⁻² s⁻¹ photosynthetically active radiation) devoid of ultraviolet-B radiation. In addition, intact and dehaired leaves showed no significant differences in absorptance in the visible spectral region, while leaf temper- ature was independent of hair removal. These results indicate that leaf hairs of O. europaea may play only a marginal role in leaf energy balance and transpiration. When the white light was supplemented with ultraviolet-B radiation (5.89 W m⁻²), however, there was a considerable decrease in the photo- synthetic rate, and a simultaneous increase in leaf resistance to water vapour in dehaired leaves. Photochemical efficiency of photosystem II, evaluated from chlorophyll fluorescence emitted from the illuminated side, was reduced in all cases, but the reduction in dehaired, ultraviolet-B treated leaves was more pronounced and irreversible, indicating that the reduction of the photosynthetic rate may result from both stomatal limitation and electron flow inhibition. Photosynthetic capacity of dehaired leaves, measured at 5% CO2, however, was not influenced by ultraviolet-B radiation. We suggest, therefore, that ultraviolet-B radiation reduces photosynthetic rates by closing the stomata, while the observed reduction in photosystem II photochemical efficiency may concern only a superficial chloroplast population, contributing negligibly to whole leaf photosynthesis. Under the conditions of our experi- ments, the protective function of the indumentum against ultraviolet-B radiation predominates over the water conservation function.
UV-B (290–320 nm) irradiation considerably reduced the cotyledon size of cucumber (Cucumis sativus L.) seedlings at 20 °C, and the extent of growth inhibition was reduced at 25 °C. At both temperatures, levels of endogenous scavengers and activities of active oxygen-scavenging enzymes were affected by UV-B irradiation. In particular, ascorbate peroxidase activity increased considerably, suggesting that active oxygen species might participate in the growth inhibition induced by UV-B irradiation. However, since no positive correlation was detected between the dependence of growth inhibition on temperature and the capacity to scavenge active species of oxygen, other mechanisms must be involved in the changes in the responses to UV-B that are related to temperature.
Sorghum (Sorghum vulgare (Pers.) cv. MSH 51) plants were grown in the field under ambient and supplemental levels of ultraviolet-B radiation (UV-B; supplemental daily dose corresponding to a 20% reduction in the stratospheric ozone column). Gas exchange characteristics, biomass, and levels of photosynthetic pigments, flavonoids, catalase, peroxidase activity, and ascorbic acid were determined to evaluate the changes induced by enhanced levels of UV-B irradiation. Gas exchange analysis indicated that one of the reasons for the decline in photosynthesis is stomatal limitation. Enhanced UV-B also caused reductions in chlorophyll and carotenoid pigments after 60 days of exposure. Concentrations of UV-B absorbing pigments increased linearly with age. UV-B irradiation also increased phenolic compounds. Catalase activity decreased, while peroxidase activity increased in response to elevated UV-B. There was a decrease in total plant biomass and ascorbic acid content of plants exposed to UV-B. Thus, an enhanced level of UV-B irradiation over a long period has a cumulative unfavourable effect on a number of physiological and biochemical processes, leading to a reduction in dry matter production.Key words: UV-B radiation, Sorghum vulgare, photosynthesis, stomatal resistance, flavonoids, peroxidase.
Exposure to UV-B at ambient or enhanced levels is known to trigger a variety of responses in all living organisms, including higher plants. Here we show that in Cucumis sativus L. UV-B radiation affects enzyme activity of key oxydative pentose phosphate pathway (OPPP) enzymes glucose-6-phosphate dehydrogenase (G6P-DH) and 6-phosphogluconate dehydrogenase (6-PGlu-DH), of key phenolic compounds enzyme phenylalanine ammonia lyase (PAL) as well as erythrose-4-phosphate, tryptophan and tyrosine levels. Furthermore, we found an increased activity of antioxidant enzymes such as peroxidase (POX) and catalase (CAT) in treated plants, with respect to the controls. In order to confirm the biochemical results, we isolated total RNA from both controls and UV-B treated plants to be used for gene expression analysis. We demonstrated that UV-B increases the gene expression level of peroxidase (POX), catalase (CAT) and phenylalanine ammonia lyase (PAL). Finally, our results are useful for understanding protective strategies against UV-B radiation and for elucidating what components are involved in stress-induced signals within the plant.
Barley (Hordeum vulgare L.) was grown in a glasshouse with 13.56 or 8.84 kJ m−2: biologically effective UV-B (280–320 nm: UV-BBE) simulating levels predicted to occur with 25 or 5% ozone depletion at 40°N latitude, with UV-A (320–400 mm), or with no supplemental irradiation. Activities of L-phenylalanine ammonia-lyase (PAL, EC 4.3.1.5). chalcone-flavanone isomerase (CFI, EC 5.5.1.6) and peroxidase (EC 1.11.1.7) were determined from the 5th through the 30th day after planting. PAL regulates diversion of L-phenylalanine into precursors for secondary phenolics. CFI regulates an early step of flavonoid biosynthesis, and peroxidase activates phenolic precursors for cross-linking and rigidifying cell walls. At all ages UV-B decreased soluble protein leaf−1 but had little effect on fresh weight or CFI activity. Exposure to UV-B decreased peroxidase activity only slightly in early growth stages but decreased it about 40% by day 30. PAL activity was highest 5 days after planting under all treatments, decreased thereafter, and was not detectable in control plants after day 10. UV-B prolonged PAL activity through day 15 in plants given the highest level of UV-B. This UV-B prolongation of PAL activity is correlated with, and is a likely underlying mechanism to explain, the UV-B- enhanced accumulation of flavonoids and ferulic acid in barley primary leaves. The results are discussed in terms of barley leaf adaptation to UV-B as developmental response dependent on conditions of plant growth.
Four dicotyledonous Astcraceac and four monocotyledonous Iridaceac species were grown from seed under three different effective ultraviolet-B (UV-B, 280–320 nm) fluenccs, which approximated those received daily over the natural growing periods of these species at their southerly and northerly distribution limits under ambient stratospheric ozone, and at the northerly limit assuming a 20% ozone depletion. Diminished photochemical efficiencies, delayed flowering, decreased flower production, pollen germination and tube growth, and reduced numbers of seeds set, accompanied by corresponding increases in mass per seed, were observed mainly in dicotyledons under elevated UV-B radiation, despite their higher foliar and pollen polyphenolic contents, their possession of trinucleatc pollen and their natural occurrence at lower latitudes than monocotyledons with binucleate pollen. The results demonstrate the difficulties in determining plant sensitivity to UV-B radiation from polyphenolic content, pollen type and natural geographic distribution, and suggest that monocotyledons possess other attributes that confer greater resilience to UV-B radiation.
With a reduced stratospheric ozone concentration, the generation of UV-tolerant plants may be of particular importance. Among different crop plants there is large variation in sensitivity to UV-B radiation. This study was undertaken to investigate the possibilities of using somaclonal variation and selection in vitro for improving UV-B tolerance in sugar beet (Beta vulgaris L.).
Sugar beet callus was exposed to UV radiation (280–320 nm, 0.863–5.28 kJ m-2 day-1, unweighted) and resultant shoots were selected from surviving cells. After establishment of the plants, they were grown under either visible radiation (114 μmol m-2 s-1 PAR) or with the addition of UV radiation (6.3 kJ m-2 day-1 biologically effective UV-B). Screening of regenerants in vivo for tolerance to UV radiation was undertaken 10 months after termination of the UV selection pressure. Screening was done visually and by using a number of physiological parameters, including chlorophyll fluorescence induction, ultraweak luminescence, pigment analysis and total content of UV-screening pigments. A clear difference between the unselected and the UV-selected somaclones was observed when visually studying the UV damage and other leaf injury. The observations were supported by the ultraweak luminescence measurements. Unselected plants showed significantly greater damage when subjected to subsequent UV radiation as compared to the selected plants. The clones subjected to UV selection pressure displayed a significantly higher concentration of UV-screening pigments under subsequent UV radiation. The unselected plants under subsequent UV treatment showed a lower carotenoid concentration when compared to selected plants. However, no significant difference between treatments was found for chlorophyll a/b, or F/Fmax, a measure of photosynthetic quantum yield.
Sugar beet (Beta vulgaris L.) plants injected with Cercospora beticota Sace. as well as non-infected plants were grown under visible light with or without ultraviolet-B (UV-B, 280–320 nm) radiation for 40 days. An interaction between UV-B radiation and Cercospora leaf spot disease was observed, resulting in a large reduction in leaf chlorophyll content, dry weight of leaf laminae, petioles and storage roots. Lipid peraxidation in leaves also increased the most under the combined treatments. This was also true for ultraweak luminescence from both adaxial and abaxial leaf surfaces. However, no correlation between lipid peroxidation and ultraweak luminescence was observed. Ultraviolet-B radiation given alone appeared to have either a stimulating effect, giving an increase in dry weight of laminae and reducing lipid peroxidation, or no effect. This lack of effect was seen in the absence of change in dry weight of storage roots and chlorophyll content relative to controls. The :study demonstrated a harmful interaction between UV-B radiation and Cercospom leaf spot disease on sugar beet.
Abstract— Intrinsic low level chemiluminescence of dark adapted intact leaves exhibits a transient enhancement of light emission when ambient air is replaced with an anaerobic atmosphere. Re establishing aerobic conditions gives rise to a complex kinetic behavior of the light emission in the post-anoxic phase. Metabolic changes within the leaf are suggested to be responsible for this phenom enon, where intactness of the leaf is found to be of crucial importance. Leaf homogenate showed nearly oxygen independent chemiluminescence. In contrast, low level chemiluminescence of UV-light damaged leaves and of chloroplast preparations was inhibited by oxygen depletion. Spectral analyses of the ultraweak light emission from the intact leaf indicates that in both aerobic and anaerobic cases, the source of the ultraweak light is the same. The similarity to the spectrum of delayed fluorescence also obtained from the leaf suggests that chlorophyll is the light emitting species.
Aquatic ecosystems produce about 50% of the global biomass and play an important role in atmospheric carbon dioxide cycling.
Since the primary producers are confined to the euphotic zone for energetic reasons, they are simultaneously exposed to short
wavelength radiation. Solar UV affects growth, reproduction, photosynthetic production and many other physiological processes.
Cyanobacteria are important ubiquitous prokaryotes which populate terrestrial and aquatic habitats. They account for up to
40 % of the marine biomass production and are important components of wet land ecosystems such as rice paddy fields. These
organisms are also highly impaired by solar UV, but they and other motile microorganisms have developed mitigating strategies
to protect themselves from this stress. One protection strategy is based on vertical migrations within the water column or
a microbial mats. However, both motility and orientation are impaired by UV radiation. Another means of protection is achieved
by the production of screening pigments including mycosporine-like amino acids (MAA) or scytonemins. MAAs are also produced
by phytoplankton and macroalgae. In several organisms action spectra were measured which indicate that MAA synthesis is induced
by UV in most cases. These sunscreen pigments prevent short wavelength radiation from reaching the UV sensitive DNA where
it induces thymine dimers. Remaining dimers are removed by photorepair which involves the enzyme photolyase. The photosynthetic
apparatus is another main target in primary aquatic biomass producers. Inhibition of the photosynthetic electron transport
chain can be determined by oxygen measurements or by pulse amplitude modulated (PAM) fluorescence. Plants reduce the potentially
deleterious effects of solar UV by decreasing the photosynthetic electron transport in photosystem II, a process called photoinhibition.
Despite the dramatic effects of even ambient solar UV on individual species and physiological responses, the effect of ozone
depletion on whole ecosystems is surprisingly low and close to the noise level induced by all other environmental factors
such as mixing layer depth, cloud cover and temperature.
From the data stated above it appears that at least a combination of an activated oncogenic pathway and an inactivated tumor
suppressor gene is needed in order for a skin cancer to arise: in SCC it is possibly an activated RTK/RAS pathway in combination
with dysfunctional P53 tumor suppression, in BCC the Hedgehog pathway with possibly dysfunctional P53, and in CM again possibly
an activated RTK/RAS in combination with inactivation of the INK4a locus. These combinations may be required, but not necessarily
sufficient for the development of a tumor. Additional oncogenic events may be necessary.
Although the skin cancers appear to be related to UV radiation, the effect of UV radiation is only unambiguously clear in
point mutations of P53 in SCC and BCC. The mutations found in the other relevant genes are of a wider variety, which may (in part) be caused by
solar UV radiation. Experiments are needed to clarify if and how UVB or UVA radiations can affect other relevant genes. Overall,
the data presently weigh most heavily toward the carcinogenic effect of UVB radiation: the latest data on experimental induction
of CM in the opossum Monodelphis domestica are not indicative of any important contribution of UVA radiation next to the dominant carcinogenicity of UVB radiation
Ultraviolet radiation is a well known damaging factor of plant photosynthesis. Here we studied the mechanism of damage induced
by the UV-B and UV-A spectral regions to the light energy converting Photosystem II (PSII) complex, which is the origin of
electron flow for the whole photosynthetic process. Our results show that the primary UV damage occurs at the catalytic Mn
cluster of water oxidation, which is most likely sensitized by the UV absorption of Mn(III) and Mn(IV) ions ligated by organic
residues. The presence of visible light enhances the photodamage of PSII, but has no synergistic interaction with UV radiation.
UV-induced damage of PSII can be repaired via de novo synthesis of the D1 and D2 reaction center protein subunits. This process is facilitated by low intensity visible light,
which thereby can protect against UV-induced damage. However, the photodamage induced by visible light at high intensity (above
1000 µEm−2s−1) cancels the protective effect. The protein repair of PSII is also retarded by the lack of DNA repair as shown in a photolyase
deficient cyanobacterial mutant.
A network of three channel dosimeters has been installed in Europe and other continents to continuously and automatically
monitor solar radiation in the UV-B (280 – 315 nm), UV-A (315 – 400 nm) and PAR (photosynthetic active radiation, 400 – 700
nm) wavelength ranges to follow long-term and short-term changes in the light climate. The instruments are housed in rugged
cases to withstand extreme environments from the polar circle to the tropics. The entrance optic is based on an integrating
sphere and the wavelength selection is done by appropriate filter and photodiode combinations. Software packages have been
developed to poll the data, display them graphically and store them. Quality control is warranted by careful and frequent
calibration of the instruments as well as national and international intercalibrations. The data are sent to a central server
in Pisa from where they can be downloaded on the Internet free of charge. The network has been in operation for the last five
years and has constantly been growing in numbers. The data are being used to extract important information on changing light
climate conditions and the development of stratospheric ozone.
The use of BSWF in assessing the ozone reduction issue is clearly highly important. Even small differences among BSWF can
have large consequences when employed in various predictions of RAF values, latitudinal gradients and in experimental design
involving lamp systems. It is unlikely that the same BSWF will be appropriate for all responses to UV radiation. Thus, realistic
testing of these BSWF under polychromatic radiation, especially under field conditions, is critical.
A number of in-vitro laboratory studies have shown that ultraviolet radiation (UVR) can produce optical changes in lens proteins that could explain at least one causal factor in some forms of cataractogenesis [1–7]. Cataracts have also been produced in rabbits from acute exposure to UVR in the 295–320 nanometer (nm) UV spectral band [8–10]. Additionally, several epidemiological and related studies have suggested a relationship between outdoor ambient UVR levels and the incidence of corneal degeneration and senile cataract [11–22]. Weale estimated that a factor of ten in the incidence rate of cataract was due to sunlight [23]. In addition to these delayed effects, one can experience the painful symptoms of snowblindness or welder’s flash (photokeratoconjuctivitis, or simply photokeratitis) from acute UV exposures.
Colored or chromophoric dissolved organic matter (CDOM) is by definition that portion of the dissolved organic matter (DOM)
capable of absorbing light (i.e. contains chromophores). It represents a dominant absorbing species in natural waters and
therefore it plays a critical role in controlling the light distribution in aquatic environments. CDOM shows a featureless
absorption spectrum that increases exponentially with decreasing wavelength. Under light exposure CDOM loses its optical properties
(photobleaching), altering the aquatic light field. Field and laboratory studies indicate that the CDOM photobleaching can
represent a quite significant sink of this material over a short time scale.
This paper reviews some of the results described in the literature on the effect of UV-B radiation on ciliated protozoa, concentrating
in particular on the changes induced in motility and photomotility, which are both important in determining the capability
of these organisms to survive in their environment. It will be shortly described what ciliates are and why they are an important
component of ecological systems. A summary will follow of the early works, where the effects of UV radiation on ciliates were
investigated. Finally, it will be described in some more detail the results of studies on a marine ciliate, Fabrea salina, and two fresh-water ciliates, Blepharisma japonicum and Ophryoglena flava.
In the last twenty years, the presence in the atmosphere of ozone-depleting substances (CFCs, HCFCs, halons, carbon tetrachloride, etc.) has been reducing the ozone concentration in the stratosphere over high and mid-latitudes of both hemispheres. Notwithstanding ozone concentration in the atmosphere is very low, the stratospheric layer, which contains approximately 90% of the total ozone, has the function of a protective filter for the Earth’s surface, cutting-off solar radiation under 280 nm and greatly reducing UV-B radiation (280-315 nm). The reduction of stratospheric ozone has been recognized as the main cause of the increase of UV-B irradiance at the Earth’s surface. This increase has been estimated in the range 6-14% in the last twenty years. Also spectral measurements performed at various sites located in Europe, North and South America, Antarctica and New Zealand have correlated UV-B radiation increase with the ozone decline. 1 UV-B has various direct adverse effects on human health (skin cancer, immunosuppression, eye disorders), terrestrial plants and aquatic organisms (DNA alterations, photosynthesis inhibition, reduced growth). Moreover, due to the differences in UV-B sensitivity and adaptation among the various species, shifts in species composition may occur as a consequence of increased UV-B radiation, thus leading indirectly to alterations in ecosystems. 2-4 As the enhancement of solar UV-B is highly wavelength specific and increases when the wavelength decreases, action spectroscopy plays a central role in assessing the effects of ozone depletion on the biosphere. 5,6 2. Action spectroscopy Action spectroscopy is a non-destructive technique for studying in vivo the absorption properties and, in some cases, the primary reactions of photoreceptors involved in triggering biological photoresponses. Action spectroscopy can be used in the investigation of any light-dependent phenomenon for which a standard response can be defined. It consists in the quantitative analysis of the response of the system as a function of the wavelength of the stimulating light and the outcome of this analysis, the action spectrum, is a measure of the relative efficiency of light of different wavelengths in inducing a defined effect on the examined biological system.
Members of the cyanobacteria are cosmopolitan in distribution, forming a prominent component of microbial populations in aquatic
as well as terrestrial ecosystems. They play a central role in successional processes, global photosynthetic biomass production
and nutrient cycling. In addition, N2-fixing cyanobacteria are often the dominant microflora in wetland soils, especially in rice paddy fields, where they significantly
contribute to fertility as a natural biofertilizer. Recent studies have shown a continuous depletion of the stratospheric
ozone layer, as a result of anthropogenically released atmospheric pollutants such as chlorofluorocarbons (CFCs) and the consequent
increase in solar UV-B radiation reaching the Earth’s surface. Considering the vital role of cyanobacteria in crop production,
the fluence rates of UV-B radiation impinging on the natural habitats are of major concern since, being photoautotrophic organisms,
cyanobacteria depend on solar radiation as their primary source of energy. UV-B radiation causes reduction in growth, survival,
protein content, heterocyst frequency and fixation of carbon and nitrogen, bleaching of pigments, disassembly of phycobilisomal
complexes, DNA damage and alteration in membrane permeability in cyanobacteria. However, a number of cyanobacteria have developed
photoprotective mechanisms to counteract the damaging effects of UV-B which includes synthesis of water soluble colourless
mycosporine-like amino acids (MAA) and the lipid soluble yellow-brown coloured sheath pigment, scytonemin. Cyanobacteria,
such as Anabaena sp., Nostoc commune, Scytonema sp. and Lyngbya sp. were isolated from rice paddy fields and other habitats in India and screened for the presence of photoprotective compounds.
Spectroscopic and biochemical analyses revealed the presence of only shinorine, a bisubstituted MAA containing both a glycine
and a serine group with an absorption maximum at 334 nm in all cyanobacteria except Lyngbya sp. There was a circadian induction in the synthesis of this compound by UV-B. A polychromatic action spectrum for the induction
of MAAs in Anabaena sp. and Nostoc commune also shows the induction to be UV-B-dependent and peaking at around 290 nm. Another photoprotective compound, scytonemin,
with an absorption maximum at 386 nm (which also absorbs significantly at 300, 278, 252 and 212 nm) was detected in all cyanobacteria
except Anabaena sp. In addition, two unidentified, water-soluble, yellowish (induced by high white light) and brownish (induced by UV-B)
compounds with an absorption maximum at 315 nm were recorded only in Scytonema sp. In conclusion, cyanobacteria having photoprotective mechanisms may be potent candidates as biofertilizers for crop plants.
IR68 and Dular rice cultivars were grown under ambient, 13.0 (simulating 20% ozone depletion) and 19.1 (simulating 40% ozone depletion) kJ m-2 day-1 of biologically effective ultraviolet-B (UV-BBE) for 4 weeks. Plant height and leaf area were significantly reduced by supplemental UV-BBE radiation. Greater reduction in leaf area than of plant height was observed. A decrease in indole-3-acetic acid (IAA) content and increase in peroxidase and IAA oxidase activities of UV-B treated plants in both cultivars were observed compared with ambient control. Calmodulin content also decreased after plants were treated with high supplemental UV-B for two weeks and medium UV-B treatment for four weeks. The results indicated that peroxidase and IAA oxidase activities in rice leaves were stimulated by supplemental UV-B, resulting in the destruction of IAA which in turn may cause inhibition of rice leaf growth. Although the mechanism is unclear, calmodulin is most likely involved in leaf growth.
The effects of UV-B radiation on photosynthesis and photosynthetic productivity of higher plants are reviewed. When plants
were exposed to large UV-B doses in a glasshouse in order to study the mechanistic basis of UV-B-induced inhibition of photosynthesis,
direct effects on stomata and on Calvin cycle enzymes (i.e. large decreases in ribulose-1,5-bisphosphate carboxylase/oxygenase
and in sedoheptulose-1,7-bisphosphate) without any significant effect on photosystem II were observed. When plants were continuously
grown and developed under UV-B in a glasshouse, exposure to UV-B only decreased adaxial stomatal conductance (gs) of the leaves and consequently increased the stomatal limitation of CO2 uptake. Furthermore, field studies using realistic UV-B levels (i.e. a predicted 30% increase in this radiation) demonstrate
a lack of UV-B effects on photosynthesis or on plant biomass. It is concluded that any predicted future increase in UV-B irradiation
is unlikely to have a significant impact on the photosynthetic characteristics and productivity of higher plants.
Sunlight is the energy source for photosynthesis in all land plants and in many aquatic organisms. On the other hand, solar
irradiation may also appear as a stress, specially when it is combined with other factors, such as deviations from optimal
growth conditions (temperature, water status) or with environmental pollutants (heavy metals, air pollutants, acidic rain).
The adaptation and acclimation of photosynthetic organisms to changing environmental conditions is important, not only for
the plant’s survival but also for manking utilising them as food, raw material and energy source. Reactive oxygen species
(ROS, also known as active oxygen species, AOS) are associated with stress and stress response in many ways: They may appear
as primary elicitors, as propagators of oxidative damage, or as by-products. More recently, ROS are also considered as messenger
molecules involved in signalling pathways, thus potential inducers of defence or adaptation. Until recently, the involvement
of ROS in stress was usually presumed from products of oxidative damage. These techniques are useful and important, but -
unlike more direct methods-they provide little information about the primary reactions. Also, due to increasing recognition
of ROS in signal transduction - when they are present at low levels and do not cause much oxidative damage - methods for direct
ROS detection in vivo are of special importance. After giving an overview on basic ROS chemistry, this chapter will illustrate direct and indirect
methods of ROS detection with special emphasis on plants and their response to UV-B (280–320 nm) irradiation.
To assess the risks to human health and ecosystems from an enhanced UV-B radiation, accurate and reliable UV monitoring systems
are required that weights the spectral irradiance according to the biological responses under consideration. Biological dosimetry
meets these requirements by directly weighting the incident UV components of sunlight in relation to the biological effectiveness
of the different wavelengths and to potential interactions between them. Bacteria, viruses and biomolecules have been developed
as biological dosimeters. Their responses to environmental UV radiation, indicated as inactivation, mutagenesis or photochemical
injury, reflect the UV sensitivity of DNA.
For assessing the applicability of a biological UV dosimeter, photobiological as well as radiometric criteria have to be met.
If radiometrically properly characterized, there is a broad scope of applications of biological UV dosimeters, which include
the determination of (i) long-term trends of biologically effective solar radiation; (ii) the contribution of the UV-B range
to the BED; (iii) the sensitivity of the biologically effective solar irradiance to ozone; (iii) vertical attenuation coefficient
of biologically effective solar irradiance in natural waters; (iv) UV tolerance and protection mechanisms; (v) the individual
UV exposure of specific professional groups.
Changes in plant growth, membrane integrity, ethylene evolution, ABA content, and the content of free polyamines were examined
in 14-day-old Arabidopsis thaliana (L.) Heynh., strain Columbia (Col-0) plants after a single UV-B irradiation with low (3 kJ/m2), moderate (6–9 kJ/m2), high (18 kJ/m2), and lethal (27 kJ/m2) doses. The UV-B treatment caused dose-dependent suppression of plant growth. One hour after irradiation, the membrane damage
was evident from the increased leakage of electrolytes. The low-dose and moderate-dose irradiation caused a transient increase
in evolution of ethylene and in the content of putrescine (spermidine and spermine precursor) with the peaks of these parameters
attained at 5 and 24 h, respectively. The high-and lethaldose irradiation induced a smaller rise in ethylene evolution, with
a slight trend to its decrease, especially, after the exposure to the lethal dose. The high and lethal doses of UV-B suppressed
putrescine accumulation, depleted spermidine and spermine pools, and caused severe injuries and plant death. During the first
day after irradiation, the ABA content increased in proportion to the irradiation dose. On the second day, the accumulation
of ABA was observed in plants irradiated with moderate doses. The accumulation was arrested after a high-dose irradiation
and was diminished by 45% after a lethal dose treatment. The results provide evidence for the involvement of ethylene, ABA,
and polyamines in plant responses induced by UV-B irradiation.
A natural protein inhibitor of guaiacol peroxidase has been partially purified from cucumber (Cucumis sativus var. Long Green) cotyledons. The inhibitor is active in vitro against commercial horse radish peroxidase (HRP) and the assay of the inhibitor at various steps of purification was performed with HRP. UV-B (280–320 nm) radiation enhances the activity of crude peroxidase in the cotyledons of cucumber but suppresses the activity of the inhibitor against HRP. The results are discussed with reference to alleviation of UV-B induced oxidative stress by peroxidase in cucumber cotyledons.
Products and byproducts of the metabolism of plant cell organelles can initiate reactions which result in radical formation. These highly active compounds are capable of emitting light or transferring excitation. If chlorophyll is present, it will probably receive excitation from the radicals and act as an emitter itself, resulting in apparently spontaneous light emission from dark-adapted plants. Spectral and kinetic data suggest that this phenomenon is different from fluorescence or delayed light emission.The aim of this work is to review new developments in the study of spontaneous ultraweak light emission from plant tissues, in particular recent evidence linking metabolic pathways to dark photoemission.
To assess the role of antioxidant defense system on exposure to ultra-violet-B (UV-B) radiation, the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of antioxidants ascorbic acid (AA) and alpha-tocopherol were monitored in cucumber (Cucumis sativus L. var long green) cotyledons. UV-B enhanced the activity of antioxidant enzymes as well as AA content, but decreased the level of alpha-tocopherol. Significant increase was observed in the activities of SOD and GPX. Analysis of isoforms of antioxidant enzymes by native-PAGE and activity staining revealed three isoforms of GPX in unexposed dark-grown cotyledons (control), and their intensity was enhanced by UV-B exposure. In addition, four new isoforms of GPX were observed in cotyledons after UV-B exposure. Although no new isoforms were observed for the other antioxidant enzymes, the activities of their existing isoforms were enhanced by UV-B.
Abstract The influence of UV-B irradiation on photosystem II activities has been investigated using isolated photosystem II membrane fragments from spinach. It was found: (a) The average amount of DCIP reduced per flash declined drastically with increasing irradiation time in the absence of DPC but remained almost unaffected in its presence, (b) After UV-B irradiation, the maximum amplitude of laser flash induced 830 nm absorption changes decreases only slightly; whereas the relaxation kinetics exhibit marked effects: the (JLS components dominate the decay at the expense of ns components. The γ.s kinetics already arise after illumination with a single flash of dark adapted samples, (c) The manganese content decreases only partly at irradiation times where the oxygen evolution capacity is almost completely lost, (d) The polypeptide pattern is hardly affected; the number of atrazine binding sites markedly decreases. Based on the results of this study, UV-B irradiation is inferred to deteriorate primarily the function of water oxidation. The action spectrum of the UV-B effect does not reveal a specific target molecule. It is assumed that structural changes of the D-l/D-2 polypeptide matrix are responsible for the modification by UV-B irradiation of the capacity of water oxidation and atrazine binding.
Root and stem segments from soybean (Merrill cv. ;Bragg') showed an enhanced chemiluminescence upon mechanical injury. Roots emitted more light than did stems. Light emission was diminished by CN(-) and N(3) (-) but was not affected by rotenone and antimycin A. Catalase quenched chemiluminescence in wounded root segments as did ascorbic acid and hydroquinone. Superoxide dismutase addition resulted in a small diminution in light emission, but mannitol, an OH. scavenger, was without effect. The addition of H(2)O(2) to wounded root segments markedly elevated chemiluminescence in the presence of air as well as under N(2). It is concluded that peroxidases, found abundantly in roots, predominantly contribute to light emission in wounded plant tissue.
Action spectra were determined for the UV-induced delay of fluorescence induction (expressed as increase of half-rise time) in leaves of Elodea densa Casp. and Oxalis deppei Lodd. Elodea leaves showed increasing sensitivity with wavelength decreasing from 310 to 280 nm, while the Oxalis leaves, when irradiated from the abaxial side, gave a rather flat spectrum with lower sensitivity than Elodea throughout the range. When Oxalis leaves were irradiated from the adaxial side, UV sensitivity was even lower. The difference is partly explainable by a higher content of water-soluble, UV-absorbing substances in the adaxial epidermis. The action spectra are compared to that determined earlier for isolated spinach thylakoids. We also analyzed in more detail the effect of ultraviolet radiation on fluorescence kinetics at selected wavelengths. The fluorescence induction in isolated spinach thylakoids is the sum of three first order processes with different time constants. The main effect of ultraviolet radiation (280 nm) is to decrease the amplitude of the intermediate component. It also slightly retards the slow component. Results with 320-nm radiation were similar.
Fluorescence induction in Elodea leaves can be described as the sum of two first order components. The main effect of 320-nm radiation was to decrease the rate constant of the slow component.
The fluorescence rise in Oxalis leaves (and also in spinach leaves) has a biphasic pattern with a plateau in the middle. It is interpreted using a model with two kinds of photosystem II units: one set of unconnected units and one set with an energy transfer probability of about 0.65. The main effect of ultraviolet radiation is to diminish the fluorescence from the unconnected units, which have the largest rate constant.
Light production by plants was confirmed by measuring chemiluminescence from root and stem tissue of peas (Pisum sativum), beans (Phaseolus vulgaris), and corn (Zea mays) in a modified scintillation spectrophotometer. Chemiluminescence was inhibited by treating pea roots with boiling ethanol or by placing them in a N2 gas phase. Chemiluminescence was increased by an O2 gas phase or by the addition of luminol. NaN3 and NaCN blocked both in vitro and in vivo chemiluminescence.It is postulated that the source of light is the hydrogen peroxide-peroxidase enzyme system. It is known that this system is responsible for chemiluminescence in leukocytes and it seems likely that a similar system occurs in plants.
Chlorophyll fluorescence in vivo was progressively lost in pea leaves irradiated with either short- or long-wave UV light. The changes were consistent with the development in the intact leaves of an inhibitory site on the photooxidizing side of photosystem II. In contrast, leaves of two species of Agave, plants regarded as more resistant to UV radiation, showed only minor changes in chlorophyll fluorescence. Agave americana was affected less than A. attenuata. The application of measurements of chlorophyll fluorescence in vivo to screening for tolerance to UV radiation is discussed.
Prolonged exposure of Allium leaves to UV light (2537 ) at low temperature induced moisture loss, breakdown of chlorophylls a and b, and of protochlorophyll. Visible light was not effective in reversing the damage. UV also caused increases in peroxidase activities in both the leaves and roots of onion plants, even though the roots were never exposed to UV light. Catalase and pyruvate kinase were inhibited as a result of UV irradiation of the leaves, while both enzymes exhibited a marked increase in the unexposed roots.
Attached or detached leaves of bean (Phaseolus vulgaris L.) were irradiated with short-wave UV light (254 nm) which resulted in increased ethylene production, increased activity of soluble and ionically bound peroxidase, increased activity of phenylalanine ammonia-lyase and an accumulation of phaseollin, accompanied by bronzing of these leaves. In order to evaluate the role of ethylene in this process, plants were pretreated with 0.5 mM aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, or with 0.45 mM 5-methyl-7-chloro-4-ethoxycarboxymethoxy-2,1,3-benzothiodiazole (DU), a presumed inhibitor of ethylene action. Both compounds showed an inhibitory effect on UV-induced ethylene production. DU stimulated UV-induced peroxidase activity, whereas AVG seemed to decrease UV-induced peroxidase activity. DU and AVG had only a weak inhibitory effect on UV-induced PAL activity. Both compounds retarded slightly the accumulation of phaseollin and the appearance of necrotic symptoms in UV-irradiated bean leaves. Ethephon treatment (500 or 1000 ppm) failed to induce the accumulation of phaseollin in attached or detached leaves of bean. The role of ethylene in UV-induced peroxidase and phenylalanine ammonia-lyase (PAL) activity and accumulation of phaseollin in bean leaves is discussed.
Sensitized fluorescence of 3,9-dibromoperylene (DBP) was obtained from triplet energy transfer with ketones as donors. The maximum efficiency of this process (TETSF) in acetonitrile measured with time-correlated single-photon counting was QTS = 0.33 ± 0.08. Because of the high quantum yield of fluorescence (QF = 0.75 ± 0.10) for analytical applications of TETSF DBP is superior to the acceptor molecules investigated earlier.Particular attention was paid to a detailed elucidation of the energy transfer processes involved in TETSF. The analysis of the excess energy dependence provided evidence for the participation of a higher excited triplet state (Tn) of DBP.
This book discusses the recent critical research on killing, mutation, and repair after exposure to far-UV and near-UV, the sublethal effects and actions on cell membranes of near-UV, the interactions of different wavelengths, and the biological action of the mid-UV.
Inhibition of primary photosynthetic reactions by UV-B radiation (280 nm-320 nm) was demonstrated in radish leaves (Raphanus sativus cv. Saxa Treib). Detached radish cotyledons from 10-day-old seedlings were irradiated with continuous white light and increasing UV-B irradiances using cut-off filters with increasing transmission for shorter wavelengths (WG 360, WG 345, WG 320, WG 305, WG 295, WG 280). Photosynthetic activity measured in terms of chlorophyll fluorescence induction (Kautsky effect) after 2, 4, 6, 8 and 24 h irradiation decreased in a wavelength dependent way with increasing UV-B irradiance and irradiation time.
Radish seedlings grown for 10 days from the time of germination under the same UV-B irradiation conditions exhibited similar reductions of the variable fluorescence as detached cotyledons irradiated for short time periods. They additionally had lower initial fluorescence at high UV-B radiation levels, although the chlorophyll content per leaf area increased. In contrast to short term experiments, the plastoquinone and flavonoid content increased with increasing UV-B irradiance when based on leaf area.
The effects of germicidal u.v. and near-u.v. irradiation on bean leaf peroxidase activity were studied by means of isoelectric focusing techniques. The results indicated that peroxidase levels can be stimulated in detached leaves by an appropriate dose of germicidal u.v. The peroxidase stimulation due to germicidal u.v. irradiation could be partially reversed by a subsequent exposure to near-u.v. Near-u.v. alone at lower exposures failed to stimulate peroxidase activity. By isoelectric focusing of samples of leaf extracts it was determined that two peroxidase isoenzymes were induced by germicidal u.v. These two isoenzymes were absent in control leaves receiving no irradiation. The isoenzymes could be induced by germicidal u.v. and then reduced in activity by exposing the leaves to near-u.v. Among several peroxidase isoenzymes induced by the tumor producing bacterial pathogen, Agrobacterium tumefaciens, two were similar in isoelectric points to the two isoenzymes induced by germicidal u.v.
The lethal effects of germicidal ultraviolet (λ=2537 Å) on the leaves of 67 species of plants were studied. A smaller number of species were examined under the simulated extraterrestrial solar radiation of a Xenon lamp at a wide range of intensities. There was an extremely large difference in sensitivity found among the various species. There was also a remarkably wide diversity in the types of adaptations and mechanisms which apparently functioned to protect against damaging light. Delicate broad-leaved plants such as Pharbitis nil and Pisum sativum were among the most sensitive plants tested, and tough-leaved xeromorphoric plants such as Agave sp. and Pinus ponderosa were among the most resistant. Grasses were moderately resistant, whereas most garden vegetables were quite sensitive. Pinus nigra which was subjected to simulated solar radiation at an intensity (0·86 cal/cm2/min) equivalent to that above the atmosphere of Mars for 44 consecutive days (635 hr) sustained very little u.v. damage. A prolonged pre-treatment with sublethal and near-lethal exposures of radiation in Xanthium leaves caused an accumulation of damage and an increase in sensitivity to a final lethal exposure. Photoreversal of u.v. damage was found in Xanthium both with u.v. alone (germicidal lamp) and with u.v. in conjunction with high-intensity visible radiation (Xenon lamp) when followed by an exposure of visible radiation. Little or no photoreversal occurred when the germicidal exposures were greater than 0·22 cal/cm2 and when the Xenon exposures were greater than 17 cal/cm2. The bronzing or darkening of irradiated leaves may be due to the formation of oxidized polymerized phenolic products subsequent to cell damage by u.v. rays.
(1) Aqueous solutions of 1–10 μM ferricytochrome c treated with 100 μM–100 mM H2O2 at pH 8.0 emit chemiluminescence with quantum yield Ф ⋍ 10−9 and absolute maximum intensity per cm3 (λ = 440), and exhibit exponential decay with a rate constant of 0.15 s−1. (2) The emission spectrum of the chemiluminescence covers the range 380–620 nm with the maximum at 460 ± 10 nm. (3) Neither cytochrome c nor haemin fluoresce in the spectral region of the chemiluminescence. In the reaction course with H2O2, a weak fluorescence in the region 400–620 nm with λmax = 465–510 nm (λexc 315–430 nm) gradually arises. This originates from tryptophan oxidation products of the formylkynurenine type or from imidazole derivatives, respectively. (4) Frozen solutions (77 K) of cytochrome c exhibit phosphorescence typical of tryptophan (λexc = 280 nm, λem = 450 nm). During the peroxidation, an additional phosphorescence gradually appears in the range 480–620 nm with λmax = 530 nm (λexc = 340 nm). This originates from oxidative degradation products of tryptophan. (5) There are no red bands in the chemiluminescence spectra of cytochrome c or haemin. This result suggests that singlet molecular oxygen is not involved in either peroxidation or chemiluminescence. (6) The haem Fe3+ group and H2O2 appear to be crucial for the chemiluminescence. It is suggested that the generation of electronically excited, light-emitting states is coupled to the production of conformational out-of-equilibrium states of peroxy-Fe-protoporphyrin IX compounds.
Influence of x‐rays on the ultraweak chemiluminescence of the mitochondria of kidney bean plants
- Gorlanov N. A.
Gorlanov, N. A. & Churmasov, A. V. 1974. Influence of
x-rays on the ultraweak chemiluminescence of the mitochondria of kidney bean plants.-Radiobiology 14: 185187.
Effect of ultraviolet and x‐ray irradiation on superlight chemiluminescence of pea sprouts
- Veselova T. V.
Veselova, T. V. & Veselovskii, V. A. 1971. Effect of ultraviolet and x-ray irradiation on superlight chemiluminescence
of pea sprouts.-Radiobiologiia (in Russian) 11: 627-630.
Edited by C. Larsson
Phvsiol. Plant. 76. 1989
Chemiluminescence of soybean seeds: Spectral analysis, temperature dependence and effect of inhibitors
- A J Varsawsky
- S Gonzales Da Silva
- R A Sanchez
, Varsawsky, A. J., Gonzales Da Silva, S. & Sanchez, R. A.
1983. Chemiluminescence of soybean seeds: Spectral analysis, temperature dependence and effect of inhibitors.Photochem. Photobiol. 38: 99-104.