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Biochemistry Of The Violaxanthin Cycle In Higher Plants
Pure and Applied Chemistry
Abstract
The biochemistry of the violaxanthin cycle in relationship to photosynthesis is reviewed. The cycle is a component of the thylakoid and consists of a reaction sequence in which violaxanthin is converted to zeaxanthin (de-epoxidation) and then regenerated (epoxidation) through separate reaction mechanisms. The arrangement of the cycle in the thylakoid is transmembranous with the de-epoxidation system situated on the loculus side and epoxidation on the outer side of the membrane. Photosynthetic activities affect turnover of the cycle but the cycle itself consists entirely of dark reactions. Light has at least two roles in de-epoxidation. It establishes through the proton pump the acidic pH in the loculus that is required for de-epoxidase activity and it induces a presumed conformational change in the inner membrane surface which determines the fraction of violaxanthin in the membrane that enters the cycle. De-epoxidation, which requires ascorbate, is presumed to proceed by a reductive-dehydration mechanism. Non-cyclic electron transport can provide the required reducing potential through the dehydroascorbate-ascorbate couple. Whether ascorbate reduces the de-epoxidase system directly or through an intermediate has not been settled. Epoxidation requires NADPH and 02 which suggests a reductive mechanism. In contrast with de-epoxidation, it has a pH optimum near neutrality. The coupling of photosynthetically generated NADPH to epoxidation has been shown. Turnover of the cycle under optimal conditions is estimated to be about two orders of magnitude below optimal electron transport rates. This low rate appears to exclude a direct role of the cycle in photosynthesis or a role in significantly affecting photosynthate levels in a back reaction. The fact that the cycle is sensitive to events both before and after Photosystem I suggests a regulatory role, possibly through effects on membrane properties. A model showing the various relationships of the cycle to photosynthesis is presented. The contrasting view that the cycle can participate directly in photosynthesis, such as in oxygen evolution, is discussed. Violaxanthin de-epoxidase has been purified. It is a lipoprotein which contains monogalactosyldiglyceride (MG) exclusively. The enzyme is a mono-de-epoxidase which is specific for 3-0H, 5-6-epoxy carotenoids that are in a 3R, 5S, 6R configuration. In addition, the polyene chain must be all-trans. A model has been presented which depicts enzymic MG in a receptor role and the stereospecific active center situated in a narrow well-like depression that can accommodate only the all-trans structure.
... One may speculate that the epoxide cycle evolved subsequently to allow the rapid removal of zeaxanthin as well as its rapid re-accumulation. All photosynthetic organisms from green and brown algae to higher plants possess the 'xanthophyll cycle' or 'violaxanthin cycle' involving the di-epoxide violaxanthin a, a monoepoxide antheraxanthin b, and the epoxide-free form zeaxanthin c (Figs. 1 and 2) [88,89,171,184,212]. Six other classes of algae possess another xanthophyll cycle, consisting of two components, the monoepoxide diadinoxanthin and an epoxide-free form diatoxanthin, in which one half of the molecule has the same structure as (half of) the zeaxanthin molecule [89,193]. ...
... In the xanthophyll cycle, zeaxanthin is formed through de-epoxidation of violaxanthin via antheraxanthin in an enzymatic reaction catalyzed by a deepoxidase [89,212] (Fig. 2). There is also a second enzyme, an epoxidase, which reconverts zeaxanthin to antheraxanthin and violaxanthin. ...
... The de-epoxidase has a pH-optimum at pH 5.2 [87,90], whereas the epoxidase exhibits maximum activity at pH 7.5 [88,181]. Since both enzymes are active in the light in vivo it was suggested that the de-epoxidase is located at the inner side of the thylakoid membrane facing the (acidic) lumen and the epoxidase at the outer side facing the (alkaline) stroma [89,184,212]. This model still awaits experimental confirmation. ...
... Chilling most likely stimulated the biosynthesis of zeaxanthin due to an increased synthesis of xanthophyll cycle pigments and increased deepoxidation to dissipate excess energy. Zeaxanthin is formed from violaxanthin via antheraxanthin by enzymatic deepoxidation in the xanthophyll cycle 36 . Similarly, some other authors reported increased zeaxanthin content as a result of chilling 23,28 . ...
... Xanthophyll pigments play an important role in the plant protection mechanism 38 . Through the xanthophyll cycle, these pigments enable thermal, non-photochemical dissipation of excess energy, and protect the photosystem II (PSII) from damage in plants exposed to chilling 36,37 . ...
The aim of the present study was to evaluate the effect of post-flowering chilling of sweet cherry ( Prunus avium L.) on the content of biochemical parameters in the leaf (chloroplast pigments, sugars and phenolics). The effect of chilling was investigated in two experiments. Potted 2-year-old trees of cv. 'Grace Star' and 'Schneiders' were exposed to one, two or three consecutive overnight chillings at an average air temperature of 4.7 °C (Experiment I), but in the following year only trees of 'Grace Star' were chilled at 2.2 °C (Experiment II), 3 to 7 weeks after flowering. The analysis of the biochemical parameters was performed by high performance liquid chromatography combined with electrospray ionization mass spectrometry. Chilling at 4.7 °C caused little or no stress, while 2.2 °C induced more intense stress with increased zeaxanthin, sugar and phenolic content in leaves, while exposure of trees to higher temperatures and closer to flowering showed no changes. Two or three consecutive overnight chilling periods increased the phenolic content and enhanced the accumulation of zeaxanthin in the leaves. Sucrose, sorbitol, fructose, total sugar, and total flavonoid content in leaves increased within 48 h after chilling. Zeaxanthin epoxidized within 24 h after one and 48 h after one and two consecutive overnight chillings.
... Papaya is an important tropical and sub-tropical fruit crop which is known for its high nutritional values like vitamins A and vitamins C [13,14]. There are two types of papaya, red-fleshed and yellow-fleshed. ...
... Violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) are the two enzymes in the xanthophyll cycle. In excess light conditions, VDE catalyzes the conversion of violaxanthin to zeaxanthin via antheraxanthin, whereas ZEP catalyzes the reverse reaction [14]. The expression of ZEP and VDE were up-regulated in color break stage of papaya, this may due to chlorophyll degradation enhanced the activity of the xanthophyll cycle to avoid severe photodamage under strong illumination. ...
Background
Red-fleshed papaya is a good material to study the different carotenoids accumulation mechanism in the peel and flesh. Although the peel and flesh of papaya closely integrated into one body, the flesh coloration changing from white to red, while the exocarp coloration changing from green to yellow. In this study, the major carotenoids accumulation and the expression patterns of key carotenoid biosynthesis pathway genes in the process of papaya fruit ripening were studied, and the carotenoid biosynthetic pathways in the yellow peel and red flesh of papaya were investigated.
Results
The carotenoid composition in papaya flesh and peel were different. The major carotenoids were lutein and β-carotene in the peel, while lycopene in the flesh. The accumulation of carotenoids, including lycopene, β-carotene, and β-cryptoxanthin were considered to cause the orange-red color of papaya cv. ‘Daqing No.10’ flesh. The color of peel changed from green to yellow because of the fast degradation of chlorophyll and the appearance of carotenoids such as lutein and β-carotene. Thirteen genes that encode enzymes in the carotenoid biosynthetic pathway were detected in papaya fruit transcriptome: two phytoene synthase (PSY1, PSY2), two phytoene desaturase (PDS1, PDS2), one ζ-carotene desaturase (ZDS), four lycopene cyclase (CYCB, LCYB1, LCYB2, LCYE), one β-carotene hydroxylase (CHYB), one carotene ε-monooxygenase (LUT1), one violaxanthin de-epoxidase (VDE), and one zeaxanthin epoxidase (ZEP). The results of RNA-Seq and RT-qPCR showed the expression of carotenoid biosynthetic pathway genes was consistent with the change of carotenoid content. Carotenoid biosynthetic pathways in the yellow peel and red flesh of papaya were analysed based on the major carotenoids accumulation and the expression patterns of key carotenoid biosynthesis pathway genes. There was only a β-branch of carotenoid biosynthesis in the flesh of papaya, while there were both α- and β-branch of carotenoid biosynthesis in papaya peel. In the process of papaya fruit ripening, the α-branch was inhibited and the β-branch was enhanced in the peel.
Conclusions
The differential carotenoid accumulation and biosynthesis pathway genes expression in peel and flesh, lay a foundation for further study and provide further insights to control fruit color and improve fruit quality and appearance.
Electronic supplementary material
The online version of this article (10.1186/s12864-018-5388-0) contains supplementary material, which is available to authorized users.
... In the 1970s, Govindjee and Papageorgiou (1971), Goedheer (1972), Papageorgiou (1975a, 1979, Harnischfeger (1977), Lavorel and Etienne (1977), Duysens (1979) and Govindjee and Jursinic (1979) were the major reviewers of different aspects of Chl a fluorescence. Knox (1975) presented theoretical considerations, andStrasser (1978) reviewed his so-called 'grouping model' of PS II units. ...
... Harry Yamamoto, who has invested years of research characterizing this cycle biochemically, concluded that it played an unknown but important regulatory role in photosynthesis (see Yamamoto, 1979;Yamamoto et al., 1999). (A photograph of Yamamoto appears in Govindjee and Seufferheld, 2002.) ...
... Also, under their growth conditions, they showed typical signs of being exposed to excessive irradiance as indicated by the low epoxidation state (EPS) of the xanthophyll cycle (Fig. 6). A low EPS is indicative of the formation of zeaxanthin as result of a high transthylakoidal proton gradient, activating the enzyme violaxanthin de-epoxidase (Yamamoto 1979;Bilger et al. 1989). It is well known that EPS follows the photochemical quantum yield of PS II under varying illumination (e.g., Bilger and Lesch 1995). ...
Main Conclusion
WHIRLY1 deficient barley plants surviving growth at high irradiance displayed increased non-radiative energy dissipation, enhanced contents of zeaxanthin and the flavonoid lutonarin, but no changes in α-tocopherol nor glutathione.
Abstract
Plants are able to acclimate to environmental conditions to optimize their functions. With the exception of obligate shade plants, they can adjust their photosynthetic apparatus and the morphology and anatomy of their leaves to irradiance. Barley ( Hordeum vulgare L., cv. Golden Promise) plants with reduced abundance of the protein WHIRLY1 were recently shown to be unable to acclimatise important components of the photosynthetic apparatus to high light. Nevertheless, these plants did not show symptoms of photoinhibition. High-light (HL) grown WHIRLY1 knockdown plants showed clear signs of exposure to excessive irradiance such as a low epoxidation state of the violaxanthin cycle pigments and an early light saturation of electron transport. These responses were underlined by a very large xanthophyll cycle pool size and by an increased number of plastoglobules. Whereas zeaxanthin increased with HL stress, α -tocopherol, which is another lipophilic antioxidant, showed no response to excessive light. Also the content of the hydrophilic antioxidant glutathione showed no increase in W1 plants as compared to the wild type, whereas the flavone lutonarin was induced in W1 plants. HPLC analysis of removed epidermal tissue indicated that the largest part of lutonarin was presumably located in the mesophyll. Since lutonarin is a better antioxidant than saponarin, the major flavone present in barley leaves, it is concluded that lutonarin accumulated as a response to oxidative stress. It is also concluded that zeaxanthin and lutonarin may have served as antioxidants in the WHIRLY1 knockdown plants, contributing to their survival in HL despite their restricted HL acclimation.
... Interestingly, bluish trees were found to harbor higher contents of total carotenoids and violaxanthin (Figure 4). Violaxanthin is the precursor of zeaxanthin via the intermediate antheraxanthin [47,48]. The reversible cyclic conversions of violaxanthin, antheraxanthin, and zeaxanthin are called the violaxanthin cycle and have been reported to have profound effects on light harvesting and light energy utilization in PSII [49]. ...
Spanish fir (Abies pinsapo Boiss.) is an endemic, endangered tree that has been scarcely investigated at the molecular level. In this work, the transcriptome of Spanish fir was assembled, providing a large catalog of expressed genes (22,769), within which a high proportion were full-length transcripts (12,545). This resource is valuable for functional genomics studies and genome annotation in this relict conifer species. Two intraspecific variations of A. pinsapo can be found within its largest population at the Sierra de las Nieves National Park: one with standard green needles and another with bluish-green needles. To elucidate the causes of both phenotypes, we studied different physiological and molecular markers and transcriptome profiles in the needles. “Green” trees showed higher electron transport efficiency and enhanced levels of chlorophyll, protein, and total nitrogen in the needles. In contrast, needles from “bluish” trees exhibited higher contents of carotenoids and cellulose. These results agreed with the differential transcriptomic profiles, suggesting an imbalance in the nitrogen status of “bluish” trees. Additionally, gene expression analyses suggested that these differences could be associated with different epigenomic profiles. Taken together, the reported data provide new transcriptome resources and a better understanding of the natural variation in this tree species, which can help improve guidelines for its conservation and the implementation of adaptive management strategies under climatic change.
... The basic idea of the xanthophyll cycle in green algae is the same as in diatoms, but the xanthophylls are different: violaxanthin and zeaxanthin are interconverted via de-epoxidation/epoxidation reactions in response to different light conditions (Yamamoto 1979;Jahns et al. 2009). The functional pH range for the violaxanthin de-epoxidase is approximately 5-6, which links its activity to electron transfer, whereas the zeaxanthin epoxidase is not affected by the pH gradient (Goss and Jakob 2010). ...
Certain sea slugs “steal” the photosynthetic cellular organelles, the plastids, from their prey algae and incorporate them, still functional, inside their own cells. These animals can then remain photosynthetic for months. The redox reactions of photosynthesis are associated with inevitable damage that needs to be constantly repaired. Running photosynthesis with plastids isolated from their algal cell should not be possible, as the algal nucleus that encodes essential maintenance proteins of the photosynthetic machinery is absent in the slug cells. How do photosynthetic sea slugs then avoid or repair the oxidative damage that their plastids should be facing? In my thesis, I have tackled this question by comparing the differences in photosynthetic electron transfer between the photosynthetic sea slug Elysia timida and the source of its plastids, the alga Acetabularia acetabulum. In addition, I compared the rates of photodamage to the plastids in the slugs and in their prey algae. I used the alga Vaucheria litorea, the prey of the slug Elysia chlorotica, to investigate the intrinsic properties of V. litorea plastids that could help explain how these plastids tolerate isolation.
... [47] It has been experimentally established that zeaxanthin is present only in trace amounts in plant organs under physiological conditions in vivo or without stress. [50] However, zeaxanthin is produced by de-epoxidation through a reversible xanthophyll cycle operation due to exposure to radiation or high light conditions. Zeaxanthin level decreases as the light decreases. ...
The chemical compositions of 15 saffron samples from 11 countries (Morocco, India, Italy, Spain, Germany, Switzerland, Iran, Lithuania, Ukraine, Australia, and Azerbaijan) were evaluated. The samples were analyzed regarding the impact of environmental factors on the composition of apocarotenoids and phenolic constituents. Quantification of saffron metabolites was carried out using high-performance liquid chromatography. It was found that the high content of chlorogenic acid (0.2 mg/g, Ukraine) and ferulic acid (0.28 mg/g, India) was controlled by the duration of solar radiation during plant development. The accumulation of caffeic acid (the higher content 4.88 mg/g, Ukraine) in stigmas depended on the average air temperature. In contrast, the total crocins content according to the correlation analysis depended on the duration of solar radiation, the solar UV index, and the soil type. Rutin was found in all samples (0.83-8.74 mg/g). The highest amount of crocins (average 382.45 mg/g) accumulated in saffron from Italy and Ukraine. Crocins, picrocrocin, safranal, and rutin can further serve as saffron quality markers. All validation parameters were satisfactory and high-performance liquid chromatography methods could be successfully applied for the composition assessment of saffron metabolites. Saffron extracts showed the highest antibacterial activity against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli (MICs 62.5-125 µg/ml).
... The thylakoid lumen, having low pH, triggers deepoxidation of violaxanthin to zeaxanthin via an intermediate, antheraxanthin (Demmig-Adams & Adams 1996). This reversible reaction, called the xanthophyll cycle, is enzymatically catalyzed (Yamamoto 1979) significantly increase thermal dissipation in the antenna complexes (Ruban et al. 2007). Many species of Bacillariophyceae, Chloromonadophyceae, Chrysophyceae, Euglenophyceae, Xanthophyceae, and Dinophyceae exhibit a similar light-stimulated conversion of diadinoxanthin to diatoxanthin (Demers et al. 1991, Olaizola et al. 1994, Brown et al. 1999, Falkowski & Raven 2007. ...
Approximately 45% of the photosynthetically fixed carbon on Earth occurs in the oceans in phytoplankton, which account for less than 1% of the world's photosynthetic biomass. This amazing empirical observation implies a very high photosynthetic energy conversion efficiency, but how efficiently is the solar energy actually used? The photon energy budget of photosynthesis can be divided into three terms: the quantum yields of photochemistry, fluorescence, and heat. Measuring two of these three processes closes the energy budget. The development of ultrasensitive, seagoing chlorophyll variable fluorescence and picosecond fluorescence lifetime instruments has allowed independent closure on the first two terms. With this closure, we can understand how phytoplankton respond to nutrient supplies on timescales of hours to months and, over longer timescales, to changes in climate.
Expected final online publication date for the Annual Review of Marine Science, Volume 14 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... The importance of carotenoids as antioxidants is demonstrated by carotenoid-deficient photosynthetic organisms being highly photosensitive, suffering extensive photooxidative damage (Aluru et al. 2009) and frequently becoming mutated as a result of 1 O 2 overproduction in the light (Ouchane et al. 1997). Zeaxanthin, among other (Yamamoto 1979). Previous studies pointed out that illuminating leaf discs in the presence of eosin, a generator of 1 O 2 , caused marked lipid peroxidation in the leaves of npq1 mutants, which are deficient in VDE, but not in the leaves of WT plants (Havaux et al. 2000). ...
The important role of polyploidy in plant evolution is widely recognized. However, many questions concerning how polyploidy affects the plant phenotype remain unexplored. To elucidate the phenotypic and molecular effects of polyploidization, we obtained hexaploids by applying colchicine to a triploid clone (Populus tomentosa × P. bolleana) × (P. alba × P. glandulosa). The highest hexaploid induction rate (3.57%) resulted from a 3-day pre-culture treatment followed by treatment with colchicine by immersing the explant in 100 mg l−1 colchicine for 96 h. Reduction of photosynthesis and chloroplast degradation was observed in leaves of the hexaploid Populus which is an indication of early senescence. To investigate the gene expression underlying how polyploidization causes premature senescence, we compared the transcriptomes of the seventeenth leaf between hexaploid and triploid Populus; the leaf position was determined on the basis of preliminary experiments. 16,403 differentially expressed genes (DEGs) were identified between the hexaploids and the triploids. Based on the transcription information, several genes involved in the circadian rhythm and redox status may play important roles in premature senescence caused by polyploidization. Additionally, the MYB, AP2/EREBP, bHLH, NAC and WRKY transcription factors (TFs) may be more important than other TFs in the premature senescence of hexaploid Populus. The transcriptome results were consistent with those of quantitative real-time polymerase chain reaction (qRT-PCR), implying credibility. This study provides insights into the molecular mechanisms of the effects of polyploidization on phenotypic variation, which may be useful for the genetic improvement of polyploid breeding.
... It is important to note here that higher pE need not imply higher LUE, since PAR at each site is varying. It is well known that high intensity of incoming PAR leads to excess of excitation energy from sunlight, owing to which the biochemical cycle of xanthophyll is affected (Yamamoto 1979). ...
In view of increasing anthropogenic influences and global changes, quantification of carbon assimilation through photosynthesis has gained tremendous significance. Precise estimation of Gross Primary Productivity (GPP) is essential for several ecosystem models and is typically done using coarser scale satellite data. The mangrove ecosystem, which offers significant protection to the coastal environment, is one of the critical habitats from a global change point of view. Light use efficiency (LUE) was measured using diurnal in situ photosynthetic rate observations for 13 dominant mangrove species for 3 seasons at each of the three mangrove dominant test-sites situated along the east and west coast of India. Variations in photosynthetic rates among these species were studied for 3 seasons that indicated varying responses of mangrove ecosystem at each site. Among all species, Rhizophora mucronata and Sonneratia apetala indicated higher values at two of the test-sites. IRS Resourcesat-2 LISS-IV datasets were used for the estimation of GPP. Mean GPP for all the sites varied from 1.2 to 7.7 g C m−2 day−1 with maximum value of 14.4 g C m−2 day−1. Mean values of GPP varied across the sites, based on its maximum LUE values and available photosynthetically active radiation (PAR). The results provide GPP values at much better spatial resolution for a threatened habitat like mangroves that typically survive in a narrow habitat along the coasts.
... Therefore, it is plausible that the activation of PsbS induces a configurational modulation of PSII-LHCII supercomplexes (8). (iv) It is well known that the HL condition induces deepoxidation of Vio (37,38). We suppose that a change of xanthophyll species can induce the configurational modulation of PSII-LHCII supercomplexes due to its different chemical structure and property. ...
An intriguing molecular architecture called the “semi-crystalline photosystem II (PSII) array” has been observed in the thylakoid membranes in vascular plants. It is an array of PSII–light-harvesting complex II (LHCII) supercomplexes that only appears in low light, but its functional role has not been clarified. Here, we identified PSII–LHCII supercomplexes in their monomeric and multimeric forms in low light–acclimated spinach leaves and prepared them using sucrose-density gradient ultracentrifugation in the presence of amphipol A8-35. When the leaves were acclimated to high light, only the monomeric forms were present, suggesting that the multimeric forms represent a structural adaptation to low light and that disaggregation of the PSII–LHCII supercomplex represents an adaptation to high light. Single-particle EM revealed that the multimeric PSII–LHCII supercomplexes are composed of two (“megacomplex”) or three (“arraycomplex”) units of PSII–LHCII supercomplexes, which likely constitute a fraction of the semi-crystalline PSII array. Further characterization with fluorescence analysis revealed that multimeric forms have a higher light-harvesting capability, but a lower thermal dissipation capability than the monomeric form. These findings suggest that the configurational conversion of PSII–LHCII supercomplexes may serve as a structural basis for acclimation of plants to environmental light.
... Therefore, it is plausible that the activation of PsbS induces the configurational modulation of PSII-LHCII supercomplexes (8). (iv) It is well known that the HL condition induces deepoxidation of Vio (37,38). We suppose that change of xanthophyll species can induces the configurational modulation of PSII-LHCII supercomplexes due to its different chemical structure and property. ...
An intriguing architecture called semi-crystalline photosystem II (PSII) array has been observed in the thylakoid membranes in vascular plants. It is an array of PSIIlight harvesting complex II (LHCII) supercomplexes only appears in the low-light, whose functional role has not been clarified. We identified PSIILHCII supercomplexes in their monomeric and multimeric forms in the low-light acclimated spinach leaves and prepared them using sucrose density gradient-ultracentrifugation in the presence of amphipol A8-35. When the leaves were acclimated to high-light, however, only monomeric forms were present. Single particle electron microscopy identified that the multimeric PSIILHCII supercomplexes were composed of two (megacomplex) or three (arraycomplex) units of PSIILHCII supercomplexes, which aligned like a fraction of the semi-crystalline array. Further characterization using fluorescence analysis revealed that multimeric forms have a higher light-harvesting capability, but a lower thermal dissipation capability than the monomeric form, suggesting such a configurational conversion of PSIILHCII supercomplexes possibly serves as a structural basis for the plants acclimation to environmental light.
... In plants and green algae, this photoprotective state is induced by acidification of the thylakoid lumen (under high light conditions), protonation of PbsS, a Photosystem II (PSII) subunit, and LHCII conformational changes (reviews [4][5][6]). The acidic lumen also induces the synthesis of zeaxanthin from violaxanthin, via the xanthophyll cycle [7,8]. By contrast, in cyanobacteria, strong blue-green light photoactivates a soluble carotenoid protein: the Orange Carotenoid Protein (OCP). ...
The phycobilisome, the cyanobacterial light harvesting complex, is a huge phycobiliprotein containing extramembrane complex, formed by a core from which rods radiate. The phycobilisome has evolved to efficiently absorb sun energy and transfer it to the photosystems via the last energy acceptors of the phycobilisome, ApcD and ApcE. ApcF also affects energy transfer by interacting with ApcE. In this work we studied the role of ApcD and ApcF in energy transfer and state transitions in Synechococcus elongatus and Synechocystis PCC6803. Our results demonstrate that these proteins have different roles in both processes in the two strains. The lack of ApcD and ApcF inhibits state transitions in Synechocystis but not in S. elongatus. In addition, lack of ApcF decreases energy transfer to both photosystems only in Synechocystis, while the lack of ApcD alters energy transfer to photosystem I only in S. elongatus. Thus, conclusions based on results obtained in one cyanobacterial strain cannot be systematically transferred to other strains and the putative role(s)of phycobilisomes in state transitions need to be reconsidered.
... Carotenoid buildup dissipates this energy excess in the form of heat which cannot be utilized for photosynthesis. Therefore, the increase in carotenoid concentration in the shade mitigates damage to the photosystem caused by low-light stress [67]. The total chlorophyll concentration also significantly increased under low light intensity, as reported in previous studies [62,68]. ...
Light and atmospheric nitrogen (N) deposition are among the important environmental factors influencing plant growth and forest regeneration. We used Quercus acutissima, a dominant broadleaf tree species native to the deciduous forests of Northern China, to study the combined effects of light exposure and N addition on leaf physiology and individual plant growth. In the greenhouse, we exposed Quercus acutissima seedlings to one of two light conditions (8% and 80% of full irradiation) and one of three N treatments (0, 6, and 12 g N m⁻² y⁻¹). After 87 d, we observed that nitrogen deposition had no significant effects on the seedlings regardless of light exposure. In addition, shade significantly reduced plant height, basal diameter, leaf number, total biomass, gas exchange capacity, and carbohydrate content. In contrast, however, shade significantly increased the amount of photosynthetic pigment, above-ground biomass allocation, and specific leaf area. There was also a hierarchical plasticity among the different seedling characteristics. Compared to traits of growth, biomass, biomass allocation and leaf morphology, the leaf physiology, including photosynthetic pigment, gas exchange, carbohydrate, and PUNE, is more sensitive to light conditions. Among the biomass allocation parameters, the leaf and root mass ratios had a relatively low phenotypic plasticity. The seedlings had high foliar physiological plasticity under various light conditions. Nevertheless, we recommend high irradiance to maintain vigorous seedling growth and, in turn, promote the restoration and reconstruction of vegetation.
... qE is the largest and fastest response to light intensity changes (forming and recovering within minutes) and it is often the most effective in protecting PSII RCs against photodamage (Ruban and Murchie 2012;Demmig-Adams et al. 2014;Goss and Lepetit 2015;Ruban 2016). It depends on the generation of a transthylakoid proton gradient (ΔpH, Krause and Behrend 1986;Noctor et al. 1993), and in vascular plants it is controlled by the activation of the protein PSII subunit S (PsbS) through the acidification of the thylakoid lumen (Li et al. 2000(Li et al. , 2004 and the operation of the (violaxanthin-antheraxanthin-zeaxanthin) xanthophyll cycle (XC, Yamamoto and Kamite 1972;Yamamoto 1979). Both PsbS and zeaxanthin act as allosteric modulators that enhance the sensitivity of PSII antenna to lumenal protons and regulate antenna conformational changes Sacharz et al. 2017). ...
Main conclusion:
The macroalga Bryopsis corticulans relies on a sustained protective NPQ and a peculiar body architecture to efficiently adapt to the extreme light changes of intertidal shores. During low tides, intertidal algae experience prolonged high light stress. Efficient dissipation of excess light energy, measured as non-photochemical quenching (NPQ) of chlorophyll fluorescence, is therefore required to avoid photodamage. Light-harvesting regulation was studied in the intertidal macroalga Bryopsis corticulans, during high light and air exposure. Photosynthetic capacity and NPQ kinetics were assessed in different filament layers of the algal tufts and in intact chloroplasts to unravel the nature of NPQ in this siphonous green alga. We found that the morphology and pigment composition of the B. corticulans body provides functional segregation between surface sunlit filaments (protective state) and those that are underneath and undergo severe light attenuation (light-harvesting state). In the surface filaments, very high and sustained NPQ gradually formed. NPQ induction was triggered by the formation of transthylakoid proton gradient and independent of the xanthophyll cycle. PsbS and LHCSR proteins seem not to be active in the NPQ mechanism activated by this alga. Our results show that B. corticulans endures excess light energy pressure through a sustained protective NPQ, not related to photodamage, as revealed by the unusually quick restoration of photosystem II (PSII) function in the dark. This might suggest either the occurrence of transient PSII photoinactivation or a fast rate of PSII repair cycle.
... These phenomena may be reduced with fluorescence emission (Schreiber and Berry 1977) and by using the xanthophyll cycle. In particular, under excess light, violaxanthin is converted rapidly via the intermediate antheraxanthin into zeaxanthin, while its reaction is reversed under low light levels and during the night (Yamamoto 1979;Hager 1980;Palliotti et al. 2015). The exchange of sensible and latent heat between the leaf and the environment is characterized by convective transport, which is commonly described as the product of a convective transport coefficient and the temperature difference between the surface and the free air. ...
Recent studies showed how the density of leaf vascular system can be involved in the performance of physiological parameters. Major veins are commonly elevated in the lower epidermis of the leaf, and this anatomical feature could play a subsidiary role in increasing heat dispersion in the surrounding environment and may help dissipate excess light energy in the leaves. The aim of this study is to analyse the role of the leaf vein network in the heat dissipation process in Vitis vinifera (L.). Major leaf veins were insulated with liquid paraffin and analysed using thermal imaging. A significantly higher temperature was found on the leaf tissues with insulated veins compared to untreated leaves. Further studies are required to assess the real contribution of the leaf vascular network in thermal dissipation.
... In particular, under high light stress conditions, the dissipation of the excess absorbed light energy occurs via the nonphotochemical quenching (NPQ) of chlorophyll fluorescence, a harmless nonradiative pathway of dissipation of energy. This defensive strategy involves the synthesis of antioxidant carotenoids, such as the secondary carotenoid astaxanthin, the pigment lutein, and the xanthophyll cycle pigments: violaxanthin, antheraxanhitn, and zeaxanthin [3][4][5][6][7]. Among the xanthophylls, also loroxanthin and fucoxanthin, mainly produced by marine strains such as Phaeodactylum and Isochrysis, have been found to be strong antioxidants. ...
... Zeaxanthin happens only in trace amounts under physiological conditions in vivo or without stress condition [29][30][31]. Nevertheless, zeaxanthin occurs upon de-epoxidation through the reversible xanthophyll cycle operation due to exposure under irradiance stress or high light condition [32,33]. Although zeaxanthin accumulates during irradiance stress, that association is normally only transient. ...
... Much of the foundational work was performed by manipulating irradiance and/or nutrient availability of greenhouse or growth chamber environments to examine the role of the xanthophyll cycle in the photoprotection of plants under stressful conditions (e.g.,Demmig et al., 1987Demmig et al., , 1988Verhoeven et al., 1997;Logan et al., 1999). These studies found that plants under increasing stress employ a greater level of xanthophyll cycle interconversion, whereby violaxanthin (V) is converted to antheraxanthin (A) and zeaxanthin (Z) via successive, enzyme-catalyzed de-epoxidations (Yamamoto, 1979). Building on the strong empirical evidence supporting a relationship between increased thermal energy dissipation (often measured as non-photochemical quenching of chlorophyll fluorescence emission[NPQ]) and the pigment pool size and conversion state ([A+Z]/[V+A+Z]) of the xanthophyll cycle (DemmigDemmig-Adams, 1998), some studies are developing an understanding of the molecular mechanisms underpinning thermal energy dissipation (see, e.g.,Sylak-Glassman et al., 2014). ...
When the capacity for photosynthesis is constrained by unfavorable growing conditions, excess absorbed light is safely lost from leaves via thermal energy dissipation -a photoprotective mechanism ubiquitous among higher plants. The relatively low irradiance conditions yet stressful growing environment of the arctic tundra suggest contrasting hypotheses regarding the necessity for plant investment in photoprotection. To examine these hypotheses, the photoprotective pigments of the xanthophyll cycle were investigated in conjunction with non-photochemical quenching (NPQ) of chlorophyll fluorescence emission in two dominant arctic shrub species, Salix pulchra and Betula nana. The xanthophyll cycle pool sizes of S. pulchra leaves were substantially higher than those reported in most other higher plant species, whereas B. nana leaves maintain modestly high xanthophyll cycle pool sizes. In addition, high retention of de-epoxidized xanthophyll cycle pigments in both species and saturation of xanthophyll cycle conversion at low-light intensities were observed and associated with high levels of NPQ. The xanthophyll cycle leaf pigment pools reported are among the first published for arctic plants and support the hypothesis that foliar xanthophyll cycle activity is greater in environments prone to harsher growing conditions.
... Light-dependent interconversions involving three xanthophylls occur within the thylakoid membranes of the chloroplasts of higher plants (Hager 1980;Siefermann-Harms 1977;Yamamoto 1979), The three xanthophylls are zeaxanthin' (dihydroxy-/3,/3-carotene), antheraxanthin" (monoepoxyzeaxanthin) and violaxanthin' (diepoxyzeaxanthin). This xanthophyll cycle, or more specifically the de-epoxidized form zeaxanthin, is involved in the protection of the photosynthetic apparatus against damage by high (excessive) light absorbed by chlorophyll (for a review, see Demmig-Adams 1990). ...
Plants, algae, and photosynthetic bacteria all contain carotenoids, which are lipid-soluble natural compounds. They can act as both light-harvesting complex and photoprotectors. Due to their nature, they are able to neutralize the effect of the presence of singlet oxygen and free radicals, acting as quenchers; for this function, an important and crucial role as an antioxidant has been attributed to a large number of carotenoids. Their production has been studied in several microalgal species, which represent a natural source of these antioxidants. In particular, Haematococcus, Chlamydomonas, Chlorella, Dunaliella, diatoms such as Phaeodactylum and Isochrysis, and dinoflagellates are able to synthesize large amounts of carotenoids. Among the most powerful antioxidant carotenoids, the xanthophylls loroxanthin, neoxanthin, lutein, violaxanthin, antheraxanthin, zeaxanthin, and α-carotene and β-carotene are the ones most synthesized under photo-oxidative stress conditions. Under physiological stresses, such as high light exposure, nutrient limitation-starvation, excessive low-high temperatures, the photosynthetic activity decreases, and different metabolic pathways are activated. The study of the physiological response to different stresses helps to understand the mechanisms which regulate the accumulation of antioxidant compounds. This information can be useful for optimizing the growth conditions of microalgal strains, the high carotenoid producers, for increasing their productivity, in terms of both antioxidants and biomass, and for the scale-up of the process from laboratory to outdoor cultures.
The quantum yield of photosynthesis (QY, CO2 fixed per light absorbed) depends on the efficiency of light absorption, the coupling between light absorption and electron transport, and the coupling between electron transport and carbon metabolism. QY is generally lower in C3 relative to C4 plants at warm temperatures and differs among the C4 subtypes. We investigated the acclimation to shade of light absorption and electron transport in six representative grasses with C3 , C3 -C4 and C4 photosynthesis. Plants were grown under full (control) or 25% (shade) sunlight. We measured the in vivo activity and stoichiometry of PSI and PSII, leaf spectral properties and pigment contents, and photosynthetic enzyme activities. Under control growth-light conditions, C4 species had higher CO2 assimilation rates, which declined to a greater extent relative to the C3 species. Whole leaf PSII/PSI ratios were highest in the C3 species, while QY and cyclic electron flow (CEF) were highest in the C4 , NADP-ME species. Shade significantly reduced leaf PSII/PSI, linear electron flow (LEF) and CEF of most species. Overall, shade reduced leaf absorptance, especially in the green region, as well as carotenoid and chlorophyll contents in C4 more than non-C4 species. The NAD-ME species underwent the greatest reduction in leaf absorptance and pigments under shade. In conclusion, shade compromised QY the least in the C3 and the most in the C4 -NAD-ME species. Different sensitivity to shade was associated with the ability to maintain leaf absorptance and pigments. This is important for maximising light absorption and minimising photoprotection under low light. This article is protected by copyright. All rights reserved.
Beginning systematically with the fundamentals, the fully-updated third edition of this popular graduate textbook provides an understanding of all the essential elements of marine optics. It explains the key role of light as a major factor in determining the operation and biological composition of aquatic ecosystems, and its scope ranges from the physics of light transmission within water, through the biochemistry and physiology of aquatic photosynthesis, to the ecological relationships that depend on the underwater light climate. This book also provides a valuable introduction to the remote sensing of the ocean from space, which is now recognized to be of great environmental significance due to its direct relevance to global warming. An important resource for graduate courses on marine optics, aquatic photosynthesis, or ocean remote sensing; and for aquatic scientists, both oceanographers and limnologists.
High temporal resolution measurements of solar‐induced chlorophyll fluorescence (F) and the Photochemical Reflectance Index (PRI) encode vegetation functioning. However, these signals are modulated by time‐dependent processes. We tested the applicability of the Singular Spectrum Analysis (SSA) for disentangling fast components (physiology‐driven) and slow components (controlled by structural and biochemical properties) from PRI, far‐red F (F760), and far‐red apparent fluorescence yield (Fy∗760). The proof of concept was developed on spectral and flux time series simulated with the Soil Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model. This allowed the evaluation of SSA decomposition against variables that are independent of physiology or are modified by it. Slow SSA‐decomposed components of PRI and Fy∗760 showed high correlations with the reference variables (R² = 0.97 and 0.96, respectively). Fast SSA‐decomposed components of PRI and Fy∗760 were better related to the physiological reference variables than the original signals during periods when leaf area index (LAI) was above 1 m² m⁻². The method was also successfully applied to predict light‐use efficiency (LUE) from the fast SSA‐decomposed components of PRI (R² = 0.70) and Fy∗760 (R² = 0.68) when discarding data modeled with LAI < 1 m² m⁻² and short‐wave radiation Rin < 250 W m⁻². The method was then tested on data acquired in a Mediterranean grassland. In this case, the fast SSA‐decomposed component of apparent LUE∗ showed a stronger correlation with the fast SSA‐decomposed component of Fy∗760 (R² = 0.42) than with original Fy∗760 (R² = 0.01). SSA‐based approach is a promising tool for decoupling physiological information from measurements acquired with automated proximal sensing systems.
The relationship between the Photochemical Reflectance Index (PRI) and Light Use Efficiency (LUE) is well established at leaf and small canopy scales, but upscaling to ecosystem level is still a challenge. Only few studies have applied satellite-derived PRI to estimate LUE, mostly using MODIS, and although the results are promising, many external factors have been identified affecting PRI performance. The present study investigates determinants and restrictions of MODIS-derived PRI potential to follow the LUE variability of a Mediterranean coniferous forest.
Daily and half-hour LUE values were calculated from eddy covariance measurements, dividing GPP by either Photosynthetically Active Radiation (PAR) or the absorbed fraction of PAR (APAR). Also, various PRI datasets were created based on different sensor (Terra, Aqua, Both), reference band (1, 12, 13) and observation/illumination angles. Overall, PRI correlated better with LUE calculated using PAR instead of APAR and Aqua PRI yielded better results than Terra. Restricting acquisitions according to observation/illumination angles improves the PRI:LUE relationship (maximum R² = 0.512), with backscatter observations yielding the best correlations. Our findings suggest that MODIS-derived PRI is more sensitive to relatively large seasonal LUE changes, but is unable to closely follow severe drought events. Among the tested reference bands, the best results were derived using band 12 (546 - 556 nm), although the optimum reference band seems to depend on viewing conditions. The PRI:LUE relationship was further improved when half-hour LUE of the satellite overpass was used instead of daily LUE. However, it was found that the PRI:LUE relationships for the different datasets were strongly affected by the range of LUE values corresponding to each PRI group, with lower LUE variability resulting to weaker PRI:LUE correlations. LUE range effect should be accounted for in future studies, when different PRI datasets are compared and might explain the contradicting findings in the existing literature.
On looking back at a lifetime of research, it is interesting to see, in the light of current progress, how things came to be, and to speculate on how things might be. I am delighted in the context of the Mitchell prize to have that excuse to present this necessarily personal view of developments in areas of my interests. I have focused on the Q-cycle and a few examples showing wider ramifications, since that had been the main interest of the lab in the 20 years since structures became available, − a watershed event in determining our molecular perspective. I have reviewed the evidence for our model for the mechanism of the first electron transfer of the bifurcated reaction at the Qo-site, which I think is compelling. In reviewing progress in understanding the second electron transfer, I have revisited some controversies to justify important conclusions which appear, from the literature, not to have been taken seriously. I hope this does not come over as nitpicking. The conclusions are important to the final section in which I develop an internally consistent mechanism for turnovers of the complex leading to a state similar to that observed in recent rapid-mix/freeze-quench experiments, reported three years ago. The final model is necessarily speculative but is open to test.
Coelastrella astaxanthina Ki-4, a eukaryotic microalga belonging to the family Scenedesmaceae, survives for long periods under severe photo-oxidative stress conditions associated with the accumulation of water-soluble astaxanthin-binding glycoprotein, named AstaP. It is a novel carotenoprotein in photosynthetic organisms and is involved in photo-oxidative stress protection, but its expression profile during cell survival and relationship with the biosynthesis of the cofactor astaxanthin are almost unknown. In this study, based on the analysis of photosynthesis during cell survival under photo-oxidative stress conditions, we classified the recovery periods of photosynthesis into the following three stages: recovery, tolerance, and cyst stages. Although C. astaxanthina Ki-4 promptly decreased the activity of photosynthesis after the start of photo-oxidative stress treatment, the activity recovered in the early recovery stage, where the expression of the transcript encoding AstaP was significantly upregulated. In the tolerant stage, red-coloration and enlargement of cells were gradually increased, and the accumulation of the AstaP protein was also significantly increased. C. astaxanthina Ki-4 cells presented a large amount of lutein before the stress treatment, which was decreased with the gradual increase in secondary carotenoids, such as canthaxanthin, adonixanthin, and astaxanthin. Although astaxanthin was quantified to be almost equal to that of the other secondary carotenoids, astaxanthin was detected as the main carotenoid binding to AstaP. These results suggest that AstaP preferentially binds to astaxanthin in vivo and contributes to photo-oxidative stress protection mainly in the tolerance stage.
Carotenoids are essential components of photosynthetic organisms including land plants, algae, cyanobacteria, and photosynthetic bacteria. Although the light-mediated regulation of carotenoid biosynthesis, including the light/dark cycle as well as the dependence of carotenoid biosynthesis–related gene translation on light wavelength, has been investigated in land plants, these aspects have not been studied in microalgae. Here, we investigated carotenoid biosynthesis in Euglena gracilis and found that zeaxanthin accumulates in the dark. The major carotenoid species in E. gracilis, namely β-carotene, neoxanthin, diadinoxanthin and diatoxanthin, accumulated corresponding to the duration of light irradiation under the light/dark cycle, although the translation of carotenoid biosynthesis genes hardly changed. Irradiation with either blue or red light (3 μmol photons m⁻² s⁻¹) caused a 1.3-fold increase in β-carotene content compared with the dark control. Blue-light irradiation (300 μmol photons m⁻² s⁻¹) caused an increase in the cellular content of both zeaxanthin and all trans-diatoxanthin, and this increase was proportional to blue-light intensity. In addition, pre-irradiation with blue light of 3 or 30 μmol photons m⁻² s⁻¹ enhanced the photosynthetic activity and tolerance to high-light stress. These findings suggest that the accumulation of β-carotene is regulated by the intensity of light, which may contribute to the acclimation of E. gracilis to the light environment in day night conditions.
Faza świetlna fotosyntezy jest kluczowym procesem energetycznym u roślin wyższych. Jej celem jest konwersja energii świetlnej w energię chemiczną w postaci ATP i NADPH, które są następnie wykorzystywane do asymilacji CO2 oraz szeregu innych procesów metabolicznych. Utrzymanie optymalnej wydajności procesu fotosyntezy wymaga ścisłej regulacji organizacji błon tylakoidów i szybkiego reagowania na zmienne warunki środowiska. Głównym czynnikiem wpływającym na wydajność fotosyntezy jest światło, które w zbyt wysokim natężeniu prowadzi do spowolnienia procesu. Dlatego rośliny wykształciły szereg mechanizmów ochronnych regulujących reakcje świetlne fotosyntezy i działających na poziomie absorpcji energii świetlnej, transportu elektronów oraz dystrybucji i wykorzystania siły redukcyjnej. Należą do nich m. in.: (i) niefotochemiczne wygaszanie energii regulujące ilość dostarczanej energii wzbudzenia; (ii) proces przejścia stanów redystrybuujący ją pomiędzy fotosystemami; (iii) redundantne szlaki transportu elektronów odpowiadające za utrzymanie równowagi redoks w chloroplastach. Wszystkie te mechanizmy, w połączeniu z systemami antyoksydacyjnymi, mają na celu utrzymanie funkcji aparatu fotosyntetycznego w niesprzyjających warunkach wzrostu.
Light harvesting is the means by which photosynthetic organisms “value-add” their ability to store solar energy in the form of organic compounds, and is one of the few ways that will lead to a sustainable future for planet Earth. This review concentrates on oxygenic photosynthetic organisms, which account of the great majority of organic matter fixed annually on the Earth. The principles of light-harvesting were laid down by cyanobacteria and their forebears, dating back to more than 3 billion years ago. However, when cyanobacteria entered into a symbiotic relationship with single celled protists to form algae, with plastids, many new light-harvesting structures evolved. The most notable advance here was the development of a three-helix membrane spanning protein which bound up to 15 chlorophylls (Chls), binding Chl a + Chl b in chlorophytes and Chl a + Chl c in chromophytes. In two other lines of algae with primary plastids, the rhodophytes and glaucophytes, phycobiliproteins are used principally, with a clear inheritance from cyanobacteria but in the case of rhodophytes, with the evolution of a new γ protein. The red algae have also donated genes to the lines of algae with secondary plastids and in one line, Cryptophytes, phycobiliproteins occur. The algae have developed a bewildering array of structures, pigments and pigment proteins. In the chlorophytes the Streptophyta gave rise to embyophytes, which inherited light-harvesting characters from them. However, the down-side of efficient light-harvesting is that it can be too efficient at times and in order to minimise photoinhibition, algae developed much more sophisticated mechanisms for down-regulating energy capture or transducing excess energy to heat; this has been brought about by specialised ways of arranging the light-harvesting proteins in the thylakoid membranes of cyanobacteria or plastids and rearranging these units for different incoming light conditions, and down-regulating excess light excitation.
The purpose of this research was to obtain recombinant violaxanthin de-epoxidases (VDEs) from two species. The first one was VDE of Arabidopsis thaliana (L.) Heynh. (WT Columbia strain) (AtVDE) which in vivo catalyzes conversion of violaxanthin (Vx) to zeaxanthin (Zx) via anteraxanthin (Ax). The second one was VDE of Phaeodactylum tricornutum Bohlin, 1897 (CCAP 1055/1 strain) (PtVDE) which is responsible for de-epoxidation of diadinoxanthin (Ddx) to diatoxanthin (Dtx). As the first step of our experiments, open reading frames coding for studied enzymes were amplified and subsequently cloned into pET-15b plasmid. For recombinant proteins production Escherichia coli Origami b strain was used. The molecular weight of the produced enzymes were estimated approximately at 45kDa and 50kDa for AtVDE and PtVDE, respectively. Both enzymes, purified under native conditions by immobilized metal affinity chromatography, displayed comparable activity in assay mixture and converted up to 90% Vx in 10 min in two steps enzymatic de-epoxidation, irrespective of enzyme origin. No statistically significant differences were observed when kinetics of the reactions catalyzed by these enzymes were compared. Putative role of selected amino-acid residues of AtVDE and PtVDE was also considered. The significance of the first time obtained recombinant PtVDE as a useful tool in various comparative investigations of de-epoxidation reactions in main types of xanthophyll cycles existing in nature are also indicated.
Mesotrione, an herbicide increasingly found in aquatic systems due to its increased application frequency in corn fields, is an inhibitor of the p-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme for plastoquinone-9, α-tocopherol and indirectly for carotenoid biosynthesis. The direct effect of mesotrione on plastoquinone-9 and α-tocopherol synthesis and their degradation rates are well documented, but few information exists on its action on photosynthetic processes under various light intensities. We therefore investigated the photosynthetic activity, energy dissipation processes, pigment composition and α-tocopherol content when Chlamydomonas reinhardtii were exposed to mesotrione for 24 h under low light condition and then the impacts of HL treatment (75 min) were also investigated. Under low light growth conditions, mesotrione did not induce PSII photoinhihition, while substantially decreased Car:Chl-a ratio, maximal energy-dependant quenching and state 1 to state 2 transition. Under high light conditions (HL), PSII activity was highly decreased in presence of mesotrione, and the non-photochemical energy dissipation processes were drastically affected in these conditions compared to the HL treatment alone. Mesotrinone also prevent the complete recovery of PSII damage caused by HL. Light condition seems therefore to be a non-negligible factor modulating mesotrione toxicity, and this has an obvious importance in agricultural waterbodies where phytoplankton is subjected to fluctuating light intensities. Mesotrione has synergistic effects with high light on pigment content and PSII activity and prevents complete recovery of photoinhibited algae.
Exposure to high light induced a quantitatively similar decrease in the rate of photosynthesis at limiting photon flux density (PFD) and of photosystem II (PSII) photochemical efficiency, FV/FM, in both green and blue-green algal lichens which were fully hydrated. Such depressions in the efficiency of photochemical energy conversion were generally reversible in green algal lichens but rather sustained in blue-green algal lichens. This greater susceptibility of blue-green algal lichens to sustained photoinhibition was not related to differences in the capacity to utilize light in photosynthesis, since the light-and CO2-saturated rates of photosynthetic O2 evolution were similar in the two groups. These reductions of PSII photochemical efficiency were, however, largely prevented in lichen thalli which were fully desiccated prior to exposure to high PFD. Thalli of green algal lichens which were allowed to desiccate during the exposure to high light exhibited similar recovery kinetics to those which were kept fully hydrated, whereas bluegreen algal lichens which became desiccated during a similar exposure exhibited greatly accelerated recovery compared to those which were kept fully hydrated. Thus, green algal lichens were able to recover from exposure to excessive PFDs when thalli were in either the hydrated or desiccated state during such an exposure, whereas in blue-green algal lichens the decrease in photochemical efficiency was reversible in thalli illuminated in the desiccated state but rather sustained subsequent to illumination of thalli in the hydrated state.
Time courses of photochemical reflectance index (PRI) of an attached cucumber leaf during a dark‐light transition were compared to those of photochemical yields of photosystem II (YII) to discuss the feasibility of PRI imaging for estimating the efficiency of photosynthetic light use. YII and PRI were simultaneously evaluated with a pulse‐amplitude modulation chlorophyll fluorometer and a low‐cost imaging system consisted of digital cameras and band‐pass filters, respectively. YII decreased immediately after the transition and then increased under various photon flux densities. Although PRI exhibited delayed time courses with respect to YII under low light conditions, PRI decreased monotonically under high light conditions. There was no correlation between YII and the changes in PRI (∆PRI) immediately after the transition but YII was correlated with ∆PRI under the steady‐state photosynthesis. These results indicate that the use of PRI to estimate YII under fluctuating light based on the regression obtained at steady state can overestimate YII. The imaging system was also applied to evaluate the spatial PRI distribution within a leaf. While PRI of leaf areas that remained untreated or had been treated with H2O again first dropped and then rose under low light and monotonically decreased under high light conditions, leaf areas treated with inhibitor (dichlorophenyl dimethylurea) did not exhibit any changes. It is likely that the inhibitor suppressed lumen acidification, which triggers a decrease in PRI. It was suggested that YII of leaves with malfunctions in the photosynthetic electron transport can be overestimated by the PRI‐based estimation.
In higher plants, carotenoids are biosynthesized in plastids by nuclear-coded enzymes. Carotenoid biosynthesis can be divided into five main stages. The early stages consist of formation of isopentenyl diphosphate (IPP) and chain elongation to geranygeranyl diphosphate (GGPP) and formation of phytoene. The later stages consist of desaturation from phytoene to lycopene, cyclization of neurosporene or lycopene, and formation of the xanthophylls. Oxygen functions are normally introduced as the final steps in carotenoid biosynthesis, forming xanthophylls. Light and its intensity have been reported to be an important factor in the regulation of carotenoid biosynthesis in plants, appearing to alter carotenogenesis by increasing the expression of some genes. With the fundamental roles of carotenoids in plant development and adaptation, their biosynthesis appears to be coordinated with other developmental processes such as plastid formation, flowering, and fruit development. Ingested carotenoids are either accumulated unchanged or are slightly modified into typical animal carotenoids.
The excess of the absorbed energy must be sufficiently dissipated to maintain the integrity of the photosynthetic apparatus. One of these protective energy dissipating mechanisms the xanthophyll epoxidation cycle working on the lumenal side of grana thylakoids recently has been thoroughly investigated in many species and under a wide range of environmental and physiological conditions [1,2,3,4].
The de-epoxidation process of violaxanthin to zeaxanthin induced by light was recognized a long time ago (Ref. 1), but it is only a recent achievement that the role of violaxanthin cycle components have been revealed as being decisive in heat dissipation of excess excitation energy in light harvesting complexes with respect to capacity for photochemical utilization (Ref. 2).
Dissipation of excess absorbed light energy as heat in the photosynthetic apparatus of higher plants is feedback regulated by limitations in the photosynthetic capacity (1–3). Although, the energy dissipation process depends on both intrathylakoid acidification and xanthophyll cycle deepoxidation (2–4) these relationships have not yet been quantified. Here we summarize a kinetic model, derived from a global analysis, that quantifies the relationships between the intrathylakoid pH, the level of xanthophyll cycle deepoxidation and the PSII chlorophyll (Chl) a fluorescence lifetime distributions and intensity. Supporting experimental results precede the model derivation and application. Details of this summary are in press elsewhere (5).
The sections in this article are
Introduction
Structure, Function and Manipulation
Biosynthesis and Regulation
Conclusions and Future Directions
Acknowledgements
Carotenoid pigments provide fruits and flowers with distinctive red, orange and yellow colours as well as a number of aromas, which make them commercially important in agriculture, food, health and the cosmetic industries. Carotenoids comprise a large family of C40 polyenes that are critical for the survival of plants and animals alike. β-carotene and its derivatives contain unmodified β-ionone groups, which serve as precursors for vitamin A and are therefore essential dietary components for mammals. Significant progress has been made towards producing staple food crops with elevated provitamin A carotenoids, an important first step in alleviating worldwide vitamin A deficiency. Recent insights into the regulatory processes that control carotenoid composition and content may further advance biofortification projects.
The eukaryotic algae display a spectacular diversity of light harvesting pigments and photosynthetic mechanisms. By contrast the Cyanobacteria on one side and the land plants on the other are uniformly dull. The Cyanobacteria make up for this relative uniformity in just one way: they have a much greater range of chlorophyll pigments, and in the case of chlorophyll d, this pigment does nearly all the heavy lifting in photosynthesis. The plastids of eukaryotic algae arose by endosymbiosis from Cyanobacteria, but during this phase of evolution, which lasted perhaps 1.5 billion years, many new structures and pigments evolved, giving the basis for the overall diversity. Three types of primary plastids occur today, the chloroplasts (Chlorophyta), the rhodoplasts (Rhodophyta) and the glaucoplasts (Glaucophyta), each with characteristic pigments and photosynthetic mechanisms. These primary lines became secondarily endosymbiotic, giving rise to secondary plastids and several evolutionary lines of eukaryotic algae. Here mention should be made of lines with chlorophyll c such as diatoms, with fucoxanthin as a main pigment, dinoflagellates with peridinin and other major members of the oceanic phytoplankton with a range of carotenoid pigments. And moving further down the evolutionary road one comes to the apicomplexans, which have lost their photosynthetic capacity but which retain an apicoplast and are important pathogens, such as the malaria organism. In all these photosynthetic, eukaryotic algae there has also been a development of mechanisms to cope with variable light, generally known as non-photochemical quenching, which is developed to a much greater extent compared to Cyanobacteria.
The main physiological function of LHCII, the largest photosynthetic antenna complex of plants, is absorption of light quanta and transfer of excitation energy toward the reaction centers, to drive photosynthesis. However, under strong illumination, the photosynthetic apparatus faces the danger of photo-degradation and therefore excitations in LHCII have to be down-regulated, e.g. via thermal energy dissipation. One of the elements of the regulatory system, operating in the photosynthetic apparatus under light stress conditions, is a conversion of violaxanthin, the xanthophyll present under low light, to zeaxanthin, accumulated under strong light. In the present study an effect of violaxanthin and zeaxanthin on the molecular organization and the photophysical properties of LHCII was studied in a monomolecular layer system with application of molecular imaging (Atomic Force Microscopy, Fluorescence Lifetime Imaging Microscopy) and spectroscopy (UV-Vis absorption, FTIR, fluorescence spectroscopy) techniques. The results of the experiments show that violaxanthin promotes formation of supramolecular LHCII structures preventing dissipative excitation quenching while zeaxanthin is involved in formation of excitonic energy states able to quench chlorophyll excitations both in the higher (B states) and lower (Q states) energy levels. The results point to a strategic role of xanthophylls, that are not embedded in a protein environment, in regulation of the photosynthetic light harvesting activity in plants.
The established functions of carotenoids in plants can all be related to their ability to absorb visible light. In the case of photosynthetic tissues they appear to have two well defined functions: (a) in photosynthesis itself and (b) in protection of the photosynthetic tissue against photosensitized oxidation. In non-photosynthetic tissues of higher plants and in fungi and non-photosynthetic bacteria, carotenoids also take part in photoprotection but the mechanism appears to be different from that in photosynthetic tissues.
Investigations were made to determine the nature of a reducing substance which was formed on illuminating a reaction system consisting of chloroplast and cytoplasmic fraction of spinach leaves. From the results of spectrophotometric examinations it was concluded that the photoproduct in question, or at least its major portion, was ascorbic acid. The precursor of ascorbic acid, which was found to be heat unstable, was contained in the cytoplasmic fraction.
