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Leaf Senescence of Postproduction Poinsettias in Low-light Stress
Abstract
Photosynthetic light harvesting was investigated under low-light stress conditions relevant to the problem of interior longevity of potted ornamental plants. Comparisons of leaf pigment levels and chlorophyll fluorescence excitation spectra were made for `Gutbier V-10 Amy' poinsettia ( Euphorbia pulcherrima Willd.), which has poor interior longevity, and `Eckespoint Lilo' poinsettia, which has superior interior longevity. The results show that `Eckespoint Lilo' had higher total chlorophyll content per leaf area and lower chlorophyll a: chlorophyll b ratio than `Gutbier V-10 Amy'. In low-light stress, `Eckespoint Lilo' retained its chlorophyll or even accumulated higher levels than in high light, while `Gutbier V-10 Amy' did not exhibit higher chlorophyll retention in low light. Both cultivars acclimatized to low-light stress by decreasing the chlorophyll a: chlorophyll b ratio, and this acclimatization was evident sooner in younger, outer-canopy leaves above the pinch than in older leaves below the pinch. Both cultivars also increased the chlorophyll: carotenoid ratio in low light. These changes in pigment composition, which were essentially structural changes, were reflected in functional changes in light harvesting, as assessed by measurements of chlorophyll fluorescence excitation spectra.
... In this study, the chl-a/chl-b ratio algae increased in Scenedesmus aldavei with the application. Due to a linear relationship between the formation of light-harvesting complex II (LHCII) aggregates and non-photochemical quenching, the chl:car ratio can be used to assess increase in LHCII (34,24,(34)(35)(36)(37). The values of some datasets published online are 2.99 in the LOPEX dataset and 3.45 in the HAWAII dataset [38]. ...
... In this study, the chl-a/chl-b ratio algae increased in Scenedesmus aldavei with the application. Due to a linear relationship between the formation of light-harvesting complex II (LHCII) aggregates and non-photochemical quenching, the chl:car ratio can be used to assess increase in LHCII (34,24,(34)(35)(36)(37). The values of some datasets published online are 2.99 in the LOPEX dataset and 3.45 in the HAWAII dataset [38]. ...
Molybdate, an oxidized form of molybdenum, facilitates molybdenum to be taken into cell, and thus to be included as a cofactor in the structure of enzymes necessary to ensure homeostasis. Although this compound provides the catalysis and electron transport of many biochemical reactions, it causes serious health problems in animals at high concentrations. For this reason, its recovery of water resources is one of the main subjects of scientific studies called bioremediaiton. One of the advantages of the remediation is that the biomass obtained from algae increases the amount of lipids, which are the raw material source for the biofuel production. For this purpose, the bioremediation abilities of Desmodesmus pannonicus and Scenedesmus aldavei algae were spectrophotometrically evaluated by using growth rate, chlorophyll-a, chlorophyll-b and total carotenoids for fourteen days. The bioremediation properties were also determined using Inductively coupled plasma - optical emission spectrometry (ICP-OES) analysis. D. pannonicus and S. aldavei algae have bioremediation capabilities up to 1 mg mL⁻¹ Na2MoO4 concentration. The lipid content increased at all concentrations in S. aldavei and at 200 μg mL⁻¹ in D. pannonicus. However, the Mo (VI) contents in dry mass changed depending on the increase of concentrations. Fourier Transform InfraRed Spectrometer analysis (FT-IR) was utilized to identify the alterations of specific functional groups such as carboxyl, amine, hydroxyl, and carbonyl in the samples. As a result, D. pannonicus and S. aldavei have great potential for Mo(VI) bioremediation. D. pannonicus and S. aldavei can tolerate Na2MoO4 up to 1 mg mL⁻¹ concentrations and the lipid content used in biofuel production was increased during this process.
... Light levels are often quite low in postproduction environments: generally brightest in supermarkets, lower in home improvement stores, and often even lower in homes away from windows. Postproduction, low light stress leading to leaf, bract, and cyathia abscission has long been studied (Embry and Nothnagel, 1994;Nell and Barrett, 1986;Shanks et al., 1970). Low temperatures are not a major issue for poinsettias in the retail environment because the optimum temperature for them is similar to that needed to keep people comfortable, but low temperatures can negatively impact plants, so it is recommended that plants be stored and shipped between 13 and 16°C (Nell et al., 1995). ...
... Selecting cultivars that are tolerant of postharvest conditions is recommended (Islam and Joyce, 2015) based on studies that have shown that cultivars can differ greatly in durability to environmental stressors (Embry and Nothnagel, 1994 Heins, 1986;Nell et al., 1997). Fourteen to 20 modern poinsettia cultivars were grown under current standard production practices to determine responses to three environmental stressors to which postproduction poinsettia plants are commonly exposed: low light levels, low temperatures, and low substrate moisture. ...
Responses of 14 to 20 poinsettia (Euphorbia pulcherrima) cultivars were assessed following exposure to environmental stressors common in the crop’s postproduction supply chain and consumer environment: low light levels, low temperatures, and low substrate moisture. As indicated by number of days to unacceptable appearance, 14 cultivars tolerated three low light levels (10, 20, and 40 µmol·m-2·s-1) well, with all individuals of six of the cultivars exhibiting an acceptable appearance at 7 weeks when the experiment ended. An experiment with 20 cultivars showed them to be surprisingly tolerant of low temperatures for a short duration, with no differences found when averaging across cultivars among plants exposed to 2, 5, or 20 °C for 2 days. However, all cultivars exposed to 5 °C for 10 days performed poorly. Cultivars differed markedly in response to low substrate moisture, with frequency of unacceptable plants before 4 weeks across all treatments ranging from 0% to 87% among the 14 cultivars tested. Across 17 cultivars, plant acceptable appearance was extended from 23 days for plants that were never irrigated after 10 days in sleeves to 32 days for plants that received a single irrigation at unsleeving and not thereafter. The low temperatures and low substrate moisture experiments were conducted in 2 years, and years differed significantly for nearly all dependent variables assessed. The significant interaction between year and cultivar for all observed variables in those two experiments indicates the importance of conducting experiments such as these over 2 years or more. Potted plants of many of the poinsettia cultivars tested proved to be highly tolerant in terms of low light levels, low temperatures, and low substrate moisture. Three cultivars appeared to be most tolerant in two of the three experiments: Prestige Red (low light levels and low temperatures), Titan Red (low temperatures and low substrate moisture), and Whitestar (low light levels and low substrate moisture). Three cultivars were most tolerant to all three sources of postproduction plant stress: Christmas Day Red, Early Mars Red, and Titan White.
... There was a linear relationship between the formation of light-harvesting complex II (LHCII) aggregates and nonphotochemical quenching [87]. The increase in chl:car implies an increase in LHCII [88]. The mean chl:car values were 5. 73, 6.11, 5.64, 4.76, and 5.31 for samples under pH 5-9 and 5.68, 7.02, 6.11, and 6.83 for samples under 0×S, 0.5×S, 1×S, and 1.5×S, respectively. ...
Japanese horseradish (wasabi) grows in very specific conditions, and recent environmental climate changes have damaged wasabi production. In addition, the optimal culture methods are not well known, and it is becoming increasingly difficult for incipient farmers to cultivate it. Chlorophyll a, b and carotenoid contents, as well as their allocation, could be an adequate indicator in evaluating its production and environmental stress; thus, developing an in situ method to monitor photosynthetic pigments based on reflectance could be useful for agricultural management. Besides original reflectance (OR), five pre-processing techniques, namely, first derivative reflectance (FDR), continuum-removed (CR), de-trending (DT), multiplicative scatter correction (MSC), and standard normal variate transformation (SNV), were compared to assess the accuracy of the estimation. Furthermore, five machine learning algorithms—random forest (RF), support vector machine (SVM), kernel-based extreme learning machine (KELM), Cubist, and Stochastic Gradient Boosting (SGB)—were considered. To classify the samples under different pH or sulphur ion concentration conditions, the end of the red edge bands was effective for OR, FDR, DT, MSC, and SNV, while a green-peak band was effective for CR. Overall, KELM and Cubist showed high performance and incorporating pre-processing techniques was effective for obtaining estimated values with high accuracy. The best combinations were found to be DT–KELM for chl a (RPD = 1.511–5.17, RMSE = 1.23–3.62 μg cm−2) and chl a:b (RPD = 0.73–3.17, RMSE = 0.13–0.60); CR–KELM for chl b (RPD = 1.92–5.06, RMSE = 0.41–1.03 μg cm−2) and chl a:car (RPD = 1.31–3.23, RMSE = 0.26–0.50); SNV–Cubist for car (RPD = 1.63–3.32, RMSE = 0.31–1.89 μg cm−2); and DT–Cubist for chl:car (RPD = 1.53–3.96, RMSE = 0.27–0.74).
... When the production crop of poinsettia plants have grown to a specified size, the plants are then exposed to shorter periods of sunlight, triggering the colour change in the bracts. 7 The controlled growing space has a roof blind, that when closed, reduces the natural light the plants are exposed to, simulating shorting days and the onset of winter. The plants react, changing colour, producing the red blooms poinsettias are known for. ...
For the current commercialized agricultural industry which requires a reduced product lead time to customer and supply all year round, an artificial light emitting diode (LED)-based illumination has high potential due to high efficiency of electrical-to-light conversion. The main advantage of the deployed Red Green Blue Amber LED lighting system is colour mixing capability, which means the ability to generate all the colours in the spectrum by using three or four primary colour LEDs. The accelerated plant growth was carried out in a “light-box” which was made to generate an artificial day/night cycle and had a capability to tune the colour mixing ratio along the colour temperature curve of the chromaticity diagram. The control group of plants form the same initial batch was grown on the same shelf in a greenhouse at the same conditions with addition of artificial illumination by incandescent lamps for few hours. More dense and better quality (hence, commercial value) plants were grown in the light-box. Costs and efficiency projections of LED lamps for horticultural applications is discussed together with required capital investment. The total cost of the “light-box” including LED lamps and electronics was 850 AUD.
... A importância económica da poinsetia como planta ornamental envasada conduziu à realização de muitos trabalhos sobre as condições de produção (Staby e Kofranek, 1979;Scott et al., 1984a;Bailey e Miller, 1991;Moe et al., 1992) e pós-produção da planta (Scott et al., 1984ab;Nell e Barret, 1986;Embry e Nothnagel, 1994) visando reduzir a abcisão de brácteas, ciátos e folhas durante o período pós-produção. Nas poinsetias submetidas a baixas intensidades luminosas, ocorre inicialmente uma maior abcisão de ciátos, seguem-se as folhas, e as brácteas. ...
... The drop of flowers and leaves is the major post-production disorder of potted plants. Although it is a natural aspect of plant life, it leads to a loss of quality and, consequently, a reduction in profit for both the producer and the seller (Embry and Northnagel, 1994;Ascough et al., 2008). Interest in the plantscape has recently increased the development of international markets for tropical foliage plants. ...
Many remote sensing-based evapotranspiration (RSBET) algorithms have been proposed in the past decades and evaluated using flux tower data, mainly over North America and Europe. Model evaluation across South America has been done locally or using only a single algorithm at a time. Here, we provide the first evaluation of multiple RSBET models, at a daily scale, across a wide variety of biomes, climate zones, and land uses in South America. We used meteorological data from 25 flux towers to force four RSBET models: Priestley–Taylor Jet Propulsion Laboratory (PT-JPL), Global Land Evaporation Amsterdam Model (GLEAM), Penman–Monteith Mu model (PM-MOD), and Penman–Monteith Nagler model (PM-VI). ET was predicted satisfactorily by all four models, with correlations consistently higher (R²>0.6) for GLEAM and PT-JPL, and PM-MOD and PM-VI presenting overall better responses in terms of percent bias (-10<PBIAS<10%). As for PM-VI, this outcome is expected, given that the model requires calibration with local data. Model skill seems to be unrelated to land-use but instead presented some dependency on biome and climate, with the models producing the best results for wet to moderately wet environments. Our findings show the suitability of individual models for a number of combinations of land cover types, biomes, and climates. At the same time, no model outperformed the other for all conditions, which emphasizes the need for adapting individual algorithms to take into account intrinsic characteristics of climates and ecosystems in South America.
In Nordic winter conditions with a shortage of natural light, it is very important to grow species and cultivars suited for low light and artificial lighting. The present study was conducted to determine if leaf net CO2-exchange, chlorophyll a fluorescence, oxygen evolution, chlorophyll a and b content, or leaf morphology would be useful in assessing gerbera (cv. 'Lamborghini,' 'Lynx' and 'Terra Regina') growth in low light. Biomass accumulation as well as flower yield was lowest in 'Lynx.' Susceptibility to photoinhibition and recovery thereafter showed small defect in 'Lynx.' The number of stomata per unit area was lowest in 'Lynx.' 'Lynx' also had higher total chlorophyll content than the other two cultivars. Surprisingly, there were no significant differences between the cultivars in chlorophyll a quenching or in leaf CO2-exchange. Chlorophyll a fluorescence, or some part of it, seems to be a possible tool to screen plants suitable for low light.
The goal of this research was to find a rapid and economic method for selecting rose (Rosa sp.) cultivars suitable for low light conditions. Cultivars Grand Prix and Tineke were used. On the basis of practical experience 'Grand Prix' is known to be more suitable for low light conditions. The cultivars were grown in two different light regimes for two weeks. Then the net carbon dioxide exchange, light compensation point and leaf chlorophyll fluorescence characteristics were measured. Also leaf anatomy and morphological features were examined. Apparently, most of the features measured are dependent both on the growth light intensity as well as on the cultivar. At low light intensity, 'Grand Prix' possessed higher photosynthetic rates, higher chlorophyll contents and higher biomass production than 'Tineke'. Thus, any of these features might have potential for a rapid screening method for low light conditions, and further studies are needed to evaluate the best method for screening plants for low light.
Pachira aquatica Aubl. has recently been introduced as an ornamental foliage plant and is widely used for interiorscaping. Its growth and use under low light conditions, however, have two problems: leaf abscission and accelerated internode elongation. This study was undertaken to determine if production light intensity and foliar application of paclobutrazol [beta-(4-chlorophenyl)methyl-alpha-(1,1-dimethylethyl)-1H- 1,2,4- triazole-1-ethanol] improved plant growth and subsequent interior performance. Two-year-old P. aquatica trunks were planted in 15-cm diameter plastic pots using a peat-based medium and were grown in a shaded greenhouse under three daily maximum photosynthetic photon flux densities (PPFD) of 285, 350, and 550 mu mol.m(-2).s(-1). Plant canopy heights, average widths, and internode lengths were recorded monthly over a 1-year production period. Two months after planting, the plant canopy was sprayed once with paclobutrazol solutions at concentrations of 0, 50, and 150 mg.L(-1), approximate to 15 mL per plant. Before the plants were placed indoors under a PPFD of 18 mu mol.m(-2).s(-1), for 6 months, net photosynthetic rates, quantum yield, and light saturation and compensation points were determined. Results showed that lowering production light levels did not significantly affect canopy height, width, or internode length but affected the photosynthetic light response curve and reduced the light compensation point. Foliar application of paclobutrazol reduced internode length, thereby resulting in plants with reduced canopy height and width and more compact growth form. Paclobutrazol application also reduced the light compensation point of plants grown under 550 mu mol.m(-2).s(-1). Plants with the compact growth form did not grow substantially, dropped fewer leaflets, and thus maintained their aesthetic appearance after placement indoors for 6 months. These results indicated that the ornamental value and interior performance of P. aquatica plants can be significantly improved by producing them under a PPFD range between 285 and 350 mu mol.m(-2).s(-1) and foliar spraying of paclobutrazol once at a concentration between 50 and 150 mg.L(-1).
The effect of methanol, ethanol, benzyladenine (BA) and paclobutrazol on retarding senescence of the leaves of cut chrysanthemum flowers and thus prolonging their vase life, was studied. All substances tested extended the vase life, limited fresh weight loss and increased chlorophyll content. Methanol applied continuously and BA as a pulse increased quantum yield of photosynthesis in the leaves. In addition, BA, and methanol to a lesser extent, prevented the formation of anthocyanins in the petals, allowing the flowers to retain their natural white color and to prolong vase life even longer. All substances, methanol in particular, caused a decrease in the Chl a:Chl b ratio, indicating a better adaptation of the photosynthetic apparatus to low light regimes, and potential capacity of these substances to facilitate acclimatization of cut flowers to interior environments. In terms of overall performance, BA as a pulse, followed by methanol, were the most effective treatments.
Although senescence remains less studied in perennials than in monocarpic plants, major advances in understanding senescence in perennials have been achieved recently. This success is due not only to the use of genetic tools in woody plants but also to a renaissance of research on how perennials can live for centuries or even millennia. The particularities of perennial life are considered here, with an emphasis on how these affect senescence at different levels of organization. I conclude that although cellular and leaf senescence do share common features in monocarpic and perennial plants, the indeterminacy of meristems found in perennials begs the question of whether senescence really occurs in these organisms at the whole-plant level.
Plant width and bract color were greater after the production period for ‘Annette Hegg Dark Red’ and ‘Gutbier V-14 Glory’ poinsettia ( Euphorbia pulcherrima Willd. ex Klotzsch) when fertilized with Osmocote 14N-6.1P-11.6K than Osmocote 18N-2.6P-10K. Plant height, width, bract color, foliar color, and plant quality increased as fertilizer rates increased from 3 to 9 g/pot. Plants fertilized with 14N-6.1P-11.6K had the least bract loss, greater fresh weight, and the best plant quality after the 30-day postharvest period. Poinsettias fertilized with the lowest rate of 3 g/pot and held for the shortest storage duration had the least leaf, bract, and cyathium loss and highest fresh weight and plant quality. Plants illuminated with the incandescent (INC) light source had the lowest leaf loss and highest fresh weight when compared to cool-white fluorescent (CWF).
Differences in cyathia abscission of poinsettias ( Euphorbia pulcherrima Willd.) ‘Annette Hegg Dark Red’ (Dark Red), ‘Annette Hegg Lady’ (Lady), ‘Annette Hegg Brilliant Diamond’ (Brilliant), ‘Gutbier V-14 Glory’ (V-14), and ‘Mikkel Triumph’ were evaluated chronologically based both on the number of days after the start of short days and on the number of days after anthesis. Seventy days after the start of short days, ‘V-14’ had the least abscission of the tested cultivars in the greenhouse or postharvest environment, while ‘Lady’ had the greatest abscission. In contrast, 7 days after anthesis, ‘V-14’ had the greatest abscission in the postharvest environment while ‘Brilliant’ and ‘Dark Red’ had the least abscission. The difference in ‘V-14’ ranking between evaluation method was due to ‘V-14’ reaching anthesis 7-10 days later than the other cultivars. Abscission was greater in the postharvest environment than in the greenhouse, probably due to the reduced photosynthetic photon flux (PPF) levels in the postharvest environment (5.1 mol·d ⁻¹ ·m ⁻² PPF in the greenhouse compared to 0.29 mol·d ⁻¹ ·m ⁻² PPF in the postharvest environment).
Low irradiance levels, high temperatures, and water stress all promoted premature cyathia abscission in poinsettia ‘Annette Hegg Dark Red’ ( Euphorbia pulcherrima Willd.). Abscission was greater in plants placed under 75% shade at 16°C night temperature (NT) than on plants placed under normal daylight (ND) at 16° or 21° NT. Water stress (0.6 MPa) promoted abscission on plants grown at an 18° NT and ND but did not promote abscission on plants grown at 16° NT and ND or on under 75% shade (13° to 21° NT). As plant density increased, transmission of photosynthetically active radiation (PAR) through the bracts to the leaf canopy decreased while cyathia abscission increased concomitantly. More than 90% of the PAR above the bracts was absorbed or reflected 5 cm below the bracts on 20 cm tall plants spaced at 65 or more plants m ⁻² . Reducing natural irradiation 75% by shading leaves of poinsettia promoted cyathia abscission, whereas removing immature bracts decreased abscission. Leaf removal on plants with intact bracts promoted abscission to a degree that 100% of the cyathia abscised prior to anthesis, whereas bract removal on plants with intact leaves resulted in only 23% abscission of the cyathia 25 days after first anthesis. Measurements of nonsoluble carbohydrate showed a significant increase in leaf carbohydrate on plants with bracts removed while carbohydrate decreased in leaves of plants with bracts intact. Carbohydrate depletion appears to be the primary factor responsible for premature cyathia abscission in poinsettia.
Euphorbia pulcherrima Willd. cvs. Mikkel Improved Rochford (MIR), Annette Hegg Dark Red (AHDR), and Gutbier V-14 Glory (GV14) were subjected to 2 storage methods (24 hours/day light or 24 hours/day darkness) for 2, 4, 6, or 8 days, and then held for a 14-day postharvest evaluation period in the greenhouse. Light-stored MIR and AHDR plants had a lower leaf drop but a higher cyathium drop as compared to dark-stored plants. GV14 was unaffected by storage methods. All cultivars retained better postharvest quality when stored for a minimal duration of time.
The effect of different growth light intensities (60 W·m ⁻² , 6 W·m ⁻² ) on the performance of the photosynthetic apparatus of mustard plants (Sinapis alba L.) was studied. A distinct decrease in photosystem II content per chlorophyll under low-light conditions compared to high-light conditions was found. For P-680 as well as for O ᴀ and O в protein the molar ratio between high-light and low-light plants was 1.4 whereas the respective concentrations per chlorophyll showed some variations for P-680 and O ᴀ on the one and O в protein on the other hand.
In addition to the study of photosystem II components, the concentrations of PQ, Cyt f, and P-700 were measured. The light regime during growth had no effect on the amount of P-700 per chlorophyll but there were large differences with respect to PQ and Cyt f. The molar ratio for Cyt f and PQ between high- and low-light leaves was 2.2 and 1.9, respectively.
Two models are proposed, showing the functional organization of the pigment system and the electron transport chain in thylakoids of high-light and low-light leaves of mustard plants.
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.
Flowering plants of several cultivars of poinsettia, Euphorbia pulcherrima Willd, were placed in darkness or low intensity artificial light to determine their influence on induction or retardation of abscission of leaves and bracts.
Photoperiod was not a factor in abscission control but abscission of leaves and bracts was induced in darkness. Light of 25 or more ft-c intensity had an effect in delaying abscission. Longer light periods were more effective and continuous 25 ft-c light was as effective in delaying abscission as 8 hr of 225 ft-c light. Continuous 225 ft-c light delayed abscission for periods up to 60 days.
Leaves tended to abscise before bracts in darkness and bracts before leaves in low intensity light. Higher light intensities were required to delay abscission following longer dark periods than following shorter or no dark storage. Leaf and bract abscission were promoted by 11 days of darkness and delayed by 75 ft-c light in cv. ‘Elisabeth Ecke’ while the long lasting cv. ‘New Ecke White’ required 16 days for promotion of leaf abscission (bract abscission was not promoted by 16 days of darkness) and 25 ft-c light was capable of delaying abscission.
Plants of Euphorbia pulcherrima Wind. `Glory' were grown under 13.4, 8.5, or 4.0 mol·m ⁻² ·day ⁻¹ and sprayed with water (control); 2500 mg·liter ⁻¹ daminozide + 1500 mg·liter ⁻¹ chlormequat chloride (D+C); 62.5 mg·liter ⁻¹ paclobutrazol; or 4, 8, 12 or 16 mg·liter ⁻¹ uniconazole to ascertain plant developmental and pest-production responses to the treatment combinations. Days to anthesis increased as irradiance was decreased. Anthesis was delayed by the D+C treatment, while other growth retardant (GR) treatments had no effect on anthesis. Irradiance did not affect plant height at anthesis, but all GR treatments decreased height over control plants. Bract display and bract canopy display diameters declined as irradiance was decreased. Growth retardants did not affect individual bract display diameters, but all GR treatments except paclobutrazol reduced bract canopy display diameter. Plants grown under lower irradiance had fewer axillary buds develop, fewer bract displays per plant, and fewer cyathia per bract display. Cyathia abscission during a 30 day post-anthesis evaluation was not affected by treatment; however, plant leaf drop was linearly proportional to irradiance. All GR treatments increased leaf drop over controls, and the D+C treated plants had the highest leaf loss. Results indicate the irradiance and GR treatments during production can affect poinsettia crop timing, plant quality at maturity, and subsequent post-production performance.
Production irradiance levels on growth, light compensation point (LCP), dark respiration (DR), and interior longevity of potted chrysanthemum (Demfranthema grandiflora Tzvelev. cvs . Iridon and Mountain Peak) and poinsettia (Euphorbia pulcherrima Wind. cvs . Annette Hegg Dark Red and Gutbier V-10 Amy) were determined. LCP and DR were measured at anthesis and during acclimatization to interior conditions (10 μmol·s ⁻¹ ·m ⁻² ). Days to flowering, inflorescence diameter, total chlorophyll, and interior longevity of chrysanthemum increased when maintained at a mean maximum photosynthetic photon flux density (PPFD) of 500 μmol·s ⁻¹ ·m ⁻² compared to plants shifted to 300 or 100 μmol·s ⁻¹ ·m ⁻² 8 weeks after planting. LCP and DR were highest at anthesis and were reduced 38% and 49%, respectively, for chrysanthemum and 19% and 42%, respectively, for poinsettia within 3 days in interior conditions. Chrysanthemum plants shifted to 300 μmol·s ¹ ·m ⁻² during production had lower LCP and DR rates at anthesis and throughout time in interior conditions compared to plants maintained at 500 μmol·s ⁻¹ ·m ⁻² . The acclimatization of chrysanthemum to reduced production PPFD is of little significance because interior longevity is reduced. No differences were found in the LCP or DR of poinsettia or chrysanthemum cultivars that differ in interior performance, demonstrating that these physiological characteristics are not good indicators of interior longevity for chrysanthemum and poinsettia.
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.
In order to study the effects of desiccation on a photosynthetic system, light harvesting and light-induced electron transport processes were examined in pea cotyledons at various moisture levels, using in vivo fluorescence excitation spectra and fluorescence induction kinetics. Water sorption isotherms yielded thermodynamic data that suggested very strong water binding between 4 to 11% water, intermediate sorption between water contents of 13 to 22%, and very weak binding at moisture contents between 24 to 32%. The fluorescence properties of the tissue changed with the moisture contents, and these changes correlated generally with the three regions of water binding. Peak fluorescence and fluorescence yield remained at low levels when water content was limited to the tightly bound regions, below 12%. Several new peaks appeared in the chlorophyll a excitation spectrum and both peak fluorescence and fluorescence yield increased at intermediate water-binding levels (12-22%). At moisture contents where water is weakly bound (>24%), peak fluorescence and fluorescence yield were maximum and the fluorescence excitation spectrum was unchanging with further increases in water content.The state of water is an important component in the energy transfer and electron transport system. At hydration levels where water is most tightly bound, energy transfer from pigments is limited and electron transport is blocked. At intermediate water binding levels, energy transfer and electron transport increase and, in the region of weak water binding, energy transfer and electron transport are maximized.
Plants of Euphorbia pulcherrima Wind. `Glory' were grown under total irradiances of 13.4, 8.5, or 4.0 mol·m ⁻² ·day ⁻¹ and sprayed with water (control), 2500 mg daminozide/liter + 1500 mg chlormequat chloride/liter (D + C), 62.5 mg paclobutrazol/liter, or 4, 8, 12, or 16 mg uniconazole/liter to ascertain plant developmental and postproduction responses to treatment combinations. Anthesis was delayed for plants grown under the lowest irradiance. Anthesis was delayed by the D + C treatment, whereas other growth retardant treatments had no effect on anthesis date. Irradiance did not affect plant height at anthesis, but all growth retardant treatments decreased height over control plants. Inflorescence and bract canopy diameters were decreased at the lowest irradiance level. Growth retardants did not affect individual inflorescence diameters, but all, except paclobutrazol and 4 and 8 mg uniconazole/liter, reduced bract canopy diameter compared with control plants. Plants grown under the lowest irradiance developed fewer inflorescences per plant and fewer cyathia per inflorescence. Cyathia abscission during a 30-day postanthesis evaluation increased as irradiance was decreased; cyathia abscission was unaffected by growth retardant treatment. Leaf abscission after 30 days postanthesis was lowest for plants grown under the lowest irradiance. At 30 days postanthesis, all growth retardant treatments increased leaf abscission over controls. Results indicate that irradiance and growth retardant treatments during production can affect poinsettia crop timing, plant quality at maturity, and subsequent postproduction performance. Chemical names used: 2-chloroethyl-N,N,N-trimethylammonium chloride (chlormequat chloride); butanedioic acid mono (2,2-dimethyl hydrazide) (daminozide); β-[(4-chlorophenyl) methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol), (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-l-penten-3-ol (uniconazole, XE-1019).
The differences in chloroplast ultrastructure, pigment composition and variable fluorescence of plants grown at low light and high light were determined, and the effect of a white light stress on the photosynthetic apparatus of LL and HL-plants and of sun and shade leaves was studied.
1.
HL-chloroplasts possess fewer thylakoids per chloroplast, lower grana stacks, a higher proportion of exposed photosynthetic membranes and a higher percentage of the photosystem I chlorophyll a/ß-carotene-proteins CPI and CPIa than LL-chloroplasts. They are characterized by higher values for the ratio chlorophyll a/b and lower values for the ratio chlorophyll a/ß-carotene (a/c), xanthophylls/ß-carotene (x/c) and chlorophylls/carotenoids. HL and sun leaves possess a smaller photosynthetic unit size, as seen from lower values for the ground fluorescence fo and the maximum fluorescence fp.
2.
A 45 min exposure of LL and HL-radish plants to a water filtered strong white light (SL: PAR 1000 μE • m–2• sec–1) does not decrease the degree of thylakoid stacking or the ratio of appressed to exposed thylakoid membranes. There occurs, however, a gradual adaptation response, as seen from an increased ß-carotene proportion, increasing a/b values together with decreasing values for a/c, x/c and a+b/x+c. Similar changes in prenyl pigment ratios were also found in Cissus leaves and in leaves of Fagus. Upon prolonged irradiation the level of photosynthetic pigments per leaf area decreases. At light+heat stress (SL + IR: strong white light without water filter) this pigment degradation proceeds faster.
Exposure to strong white light causes photo-inhibition of the photosynthetic apparatus and decreases ground fluorescence and variable fluorescence, before any decrease in chlorophyll content can be detected. It is assumed that high light stress causes the fast activation or accumulation of quencher molecules (e.g. ß-carotene or others) which protect the photosynthetic apparatus by quenching excitation energy.
Leaf development and senescence in proso millet (Panicum miliaceum L.) has been investigated for leaves from intact plants, for excised leaf segments induced to senesce by dark treatment, and for leaves on water-stressed plants. For well-watered plants, the amount of leaf chlorophyll, soluble protein, and α-NH2 nitrogen increased after emergence, and then indicated no appreciable changes due to senescence through the time of seed filling in the main panicle. Total chlorophyll and soluble protein decreased and α-NH2 nitrogen increased during dark-induced senescence of detached segments, while all three of these constituents decreased with drought-accelerated senescence of intact leaves. As either dark-induced or drought-accelerated senescence proceeded, chlorophyll a and b levels decreased steadily, with the a/b ratio decreasing significantly only after the total chlorophyll concentration had been reduced by more than 85%. As measured after extraction directly from leaf tissue, total carotenoid levels were nearly stable throughout senescence. As measured after extraction from thylakoid preparations, however, carotenoid levels did decrease with senescence, although not as sharply as the decrease in chlorophyll levels. These results are consistent with carotenoid loading into the plastoglobuli during senescence.Seed-to-seed cycles as short as 32 days were observed when proso millet was grown in a greenhouse. The rapid development of this plant makes it a convenient model system for additional studies of senescence and other physiological or genetic phenomena.
Chlorophyll fluorescence emission spectra and the kinetics of 685 mm fluorescence emission from wheat leaf tissue and thylakoids isolated from such tissue were examined as a function of excitation wavelength. A considerable enhancement of fluorescence emission above 700 nm relative to that at 685 nm was observed from leaf tissue when it was excited with 550 nm rather than 450 nm radiation. Such excitation wavelength dependent changes in the emission spectrum occurred over an excitation spectral range of 440–660 nm and appeared to be directly related to the total quantity of radiation absorbed at a given excitation wavelength. Experiments with isolated thylakoid preparations demonstrated that changes in the fluorescence emission spectrum of the leaf were attributable to the optical properties of the leaf and were not due to the intrinsic characteristies of the thylakoid photochemical apparatus. This was not the case for the observed excitation wavelength dependent changes in the 685 nm fluorescence induction curve obtained from leaf tissue infiltrated with DCMU. Excitation wavelength dependent changes in the ratio of the variable to maximal fluorescence emission and the shape of the variable fluorescence induction were observed for leaf tissue. Isolated thylakoid studies showed that such changes in the leaf fluorescence kinetics were representative of the way in which the photochemical apparatus in vivo was processing the absorbed radiation at the different excitation wavelengths. The results are considered in the context of the use of fluorescence emission characteristics of leaves as non-destructive probes of the photochemical apparatus in vivo.
Activation spectra of photochemical reactions were measured by a flash spectrophotometer in leaves having varying chlorophyll contents at different stages of greening. The increase of chlorophyll concentration up to 30 nmol cm-2 elevated the rates of photochemical reactions at all wavelengths of light used, and was found to be produced by an increase in the amounts of reaction centres. Further accumulation of chlorophyll up to 40 nmol cm-2 was associated with an increase in light-harvesting chlorophyll, an improved rate of photochemical reactions around 600 nm and at 700 nm, and self-absorption and screening effects where chlorophyll absorbed maximally (400–450 nm and around 680 nm).
Siefermann-Harms, D. 1987. The light-harvesting and protective functions of carotenoids in photosynthetic membranes.
Abstract Alterations in the composition and structure of thylakoids were studied in Brassica rapa ssp. oleifera grown under high and low irradiance (800 μmol m−2 s−1 and 80 μmol m−2 s−1). During ageing, both high and low light induced a decrease in total protein particle density and in the relative amount of 80–90 Å cytochrome b6/f and 90–100 Å ATP-synthetase. The density of PSII complexes in stacked (EFs) and unstacked (EFu) thylakoids also decreased. In high light, a shift was noted towards smaller PSII complexes in the EFs face with decreasing attached antenna complex CP29, but the relative amount of the antenna chlorophyll a-protein complexes of photosystem II (CPa) remained stable. In contrast, the proportion of peripheral LHCH on the PFs face and the density of PFs particles increased together with an increase in grana size. In low light, a shift occurred towards larger PSII complexes on the EFs face, along with a decrease in the proportion of CPa complexes and the PFs particle density (peripheral LHCH), though a marked increase was observed in the proportion of chlorophyll a/b-protein complexes in SDS-PAGE. The amount of photosystem I in green gel remained fairly stable, although the density of PFu particles (including PSI) increased in low and slightly diminished in high light. The results indicate that the organization of thylakoid components depends strongly on the light conditions and stage of development.
Excitation energy absorbed by carotenoid pigments is not transferred to newly formed chlorophyll a in etiolated leaves. The capacity for energy transfer develops during a dark period following the photoconversion of protochlorophyll. This presumably is the time required for the formation of lamellae which incorporate both the carotenoid and chlorophyll into the same structure. A sequence of events occurring in the formation of lamellae is proposed.
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A procedure for recording corrected fluorescence excitation spectra to wavelengths as long as 800 nm is described. The procedure involves the use of a commercial spectrofluorometer, which is modified by substituting 1,1',3,3,3',3'-hexamethylindotricarbocyanine perchlorate in place of rhodamine B as the quantum counter dye. This modification is applicable to spectrofluorometers supplied by several different manufacturers and can be accomplished by a user having only modest technical skills. A study of the fluorescence excitation spectrum of bacteriochlorophyll a is presented as an illustration of the use of the procedure. The procedure will be valuable in biological and biochemical studies that involve the use of long-wavelength fluorescent probes of either natural or synthetic origin.
Fluorescence action spectra were determined, both at room temperature and at liquid nitrogen temperature, with various blue-green, red and green algae, and greening bean leaves. The action spectra of algae were established with samples of low light absorption as well as dense samples. Fluorescence at room temperature, with a maximum at about 685 mμ, was for the greater part emitted by a short wave "form" of chlorophyll a, possibly Ca670. To this form energy was transferred from β-carotene, chlorophyll b and phycobilins with an efficiency approaching 100%. The action spectra of blue-green algae suggested the presence of a 650-mμ phycocyanin "form", which seemed bound more firmly to the photosynthetic apparatus than the bulk of phycocyanin absorbing around 620 mμ. The absence of action in the carotenoid region in blue-green and red algae and in bean leaves shortly after transformation of protochlorophyll to chlorophyll is ascribed to the presence of a high percentage of xanthophyll, presumably inactive in transferring energy to chlorophyll. All pigments active in producing the 685-mμ room temperature fluorescence band were found to be active in producing the 720-mμ low temperature fluorescence band. Additionally, the 720-mμ fluorescence band was excited by absorption in long wavelength chlorophyll a forms (e.g. Ca680 and Ca695) and, in blue-green and red algae, by one or more unidentified pigments with absorption maximum at 475 and 520 mμ. Marked differences between "high density" action spectra of blue-green and green algae are described.
Quantasomes obtained by sonication from the pigmented lamellae of spinach chlorplasts are observed to form aqueous suspensions which have absorption spectra corresponding closely to those of whole chloroplasts and intact leaves. The principal chlorophyll a absorption maxima at 678.5 and 437 mμ are not shifted from their position in vivo. The quantasome preparations have the advantage of giving very little light-scattering; the measured turbidity in the red is less than 1% of the absorbancy at 678.5 mμ.Aqueous suspensions of spinach quantosomes at 2° are observed to bleach rapidly in the light and slowly (over a period of 1 day) upon aging in the dark. In both cases the bleaching of chlorophyll a is accompanied by a slow shift of the red absorption band toward shorter wavelenghts. The dark bleaching has been studied in some detail. Removal of air from the suspensions markedly retards the dark bleaching, suggesting that it is an oxidation phenomenon. Spectra taken at successive intervals show that, in the dark, bleaching of the carotenoids precedes that of the chlorophylls. Difference spectra indicate that the absorption due to the carotenoids in the quantasomes possesses maxima at 485, 455 and 428 and a shoulder at 400 mμ. These maxima are 10–15 mμ to longer wavelengths from those in the ether-solution spectra of xanthophylls—the predominant carotenoids in spinach chloroplasts. A peak which appears at 470 mμ in the absorption spectra of the partially bleached quantasomes is attributed to the Soret band of chlorophyll b, which is not rapidly bleached in the dark. The rate of dark bleaching increases strongly with increasing temperature and is effectively inhibited by the presence of the soluble, colorless stroma substances. The dark bleaching is felt to be a complex phenomenon and a complete explanation must await further investigations.
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Where are we in improving flowering potted plant quality and longevity?
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