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First published online February 12, 2004; 10.1104/pp.103.032375 Plant Physiology 134:1163-1172 (2004) © 2004 American Society of Plant Biologists Ascorbate-Deficient Mutants of Arabidopsis Grow in High Light Despite Chronic Photooxidative Stress1Department of Plant and Microbial Biology, University of California, Berkeley, California 94720
Acclimation to changing environments, such as increases in light intensity, is necessary, especially for the survival of sedentary organisms like plants. To learn more about the importance of ascorbate in the acclimation of plants to high light (HL), vtc2, an ascorbate-deficient mutant of Arabidopsis, and the double mutants vtc2npq4 and vtc2npq1 were tested for growth in low light and HL and compared with the wild type. The vtc2 mutant has only 10% to 30% of wild-type levels of ascorbate, vtc2npq4 has lower ascorbate levels and lacks non-photochemical quenching of chlorophyll fluorescence (NPQ) because of the absence of the photosystem II protein PsbS, and vtc2npq1 is NPQ deficient and also lacks zeaxanthin in HL but has PsbS. All three genotypes were able to grow in HL and had wild-type levels of Lhcb1, cytochrome f, PsaF, and 2-cysteine peroxiredoxin. However, the mutants had lower electron transport and oxygen evolution rates and lower quantum efficiency of PSII compared with the wild type, implying that they experienced chronic photooxidative stress. The mutants lacking NPQ in addition to ascorbate were only slightly more affected than vtc2. All three mutants had higher glutathione levels than the wild type in HL, suggesting a possible compensation for the lower ascorbate content. These results demonstrate the importance of ascorbate for the long-term acclimation of plants to HL.
During the course of their life cycle, plants are exposed to a varying light environment, such as slow seasonal changes and a sudden increase in light intensity because of an opening in the leaf canopy. Plants have been evolving to cope with this changing light environment in a way that not only enables them to harvest light optimally but also to protect themselves from excess light. Excess absorbed light is dangerous to plants because it can lead to the enhanced production of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), superoxide, hydroxyl radicals, and singlet oxygen (Niyogi, 1999  ), which can damage many cellular components (Foyer, 1997), including PSII and PSI.
Much is already known about how plants acclimate to high light (HL). Important responses include a reduction in the size of the light-harvesting complex and an increase in the rate of photosynthesis, which correlates with increases in ATP synthase, electron transport components, and Calvin-Benson cycle enzymes (Anderson and Osmond, 1987
One very fast response to an increased light intensity is non-photochemical quenching of chlorophyll (Chl) fluorescence (NPQ), which dissipates excess energy as heat (Müller et al., 2001
Antioxidants are molecules that function to reduce oxidative stress by scavenging or quenching ROS. The main antioxidants in the chloroplast are ascorbate (vitamin C) and glutathione, which are water-soluble, and
Ascorbate is found in concentrations of up to 25 mM (Smirnoff, 2000a We were interested in elucidating the importance of various photoprotective mechanisms for HL growth. In this paper, we studied the growth of a series of ascorbate-deficient single and double mutants under conditions of HL. The vtc2 single mutant only lacks ascorbate, the double mutant vtc2npq4 also lacks qE, and the double mutant vtc2npq1 lacks ascorbate, zeaxanthin, and qE. Here, we show that these ascorbate-deficient strains were not able to acclimate fully to HL and exhibited symptoms of chronic photooxidative stress, despite showing higher glutathione levels when grown in HL. The double mutants, on the other hand, were only slightly more affected than vtc2.
Ascorbate-Deficient Mutants Were Smaller and Had Fewer Leaves All genotypes matured much faster when grown in HL (1,800 µmol photons m-2 s-1) at a photon flux density (PFD) that was nearly equivalent to full sun-light. As shown in Figure 1, the HL-grown plants were only one-third of the size of plants grown in LL (180 µmol photons m-2 s-1) at the time of sampling. Because of the difference in flowering time, HL-grown plants were sampled at the age of 4 weeks, whereas LL-grown plants were sampled at the age of 6 weeks. HL-grown plants had thicker leaves than LL-grown plants because of additional cell layers and larger cells, but the ascorbate-deficient mutants all had thinner leaves than the wild type when grown in LL or in HL (data not shown).
All genotypes showed a decrease in rosette diameter and leaf number when grown in HL (Table I). Ascorbate-deficient mutants were 30% smaller than the wild type and had 20% fewer leaves in both light regimes (Table I). There was no difference in the number of leaves between vtc2, vtc2npq4, and vtc2npq1 in LL or HL, although there were small differences in the rosette diameter between the ascorbate-deficient mutants when grown in LL. Per leaf area, the leaf mass of HL-grown leaves was nearly twice that of LL-grown leaves (data not shown) because of higher leaf thickness. Stomatal index, which is known to be responsive to environmental effects on photosynthesis (Gray et al., 2000
The maximum efficiency of PSII photochemistry was measured as the fluorescence parameter in the dark-adapted state Fv/Fm. In LL, all genotypes showed a value of 0.82, which is the typical value for uninhibited Arabidopsis plants. When grown in HL, wild-type plants maintained an Fv/Fm of 0.82, whereas all ascorbate-deficient mutants appeared to have a chronically lower PSII efficiency (Fig. 2A), with Fv/Fm values of 0.73 (vtc2) or 0.67 (vtc2npq4 and vtc2npq1).
Similarly, photosynthesis rates in ascorbate-deficient mutants did not show full acclimation to HL. Photosynthesis rates were determined by two methods. We used oxygen evolution to determine the whole-chain electron transport activity and used Chl fluorescence measurements to determine the efficiency of PSII electron transport (
To learn more about the photoprotective response to HL, we also measured NPQ in LL- and HL-grown plants. As can be seen in Figure 3C, when grown in LL, wild-type plants exhibited the highest amount of NPQ (2.5), followed by the vtc2 mutant. Both double mutants reached NPQ levels of approximately 1 at the highest PFD, with the vtc2npq4 mutant having less NPQ than the vtc2npq1 mutant. The NPQ measured in the two double mutants is of a different type than that in the wild type or vtc2 because only state transitions (qT) and photo-inhibitory quenching (qI) are contributing to it, whereas most of the NPQ in the wild type and the vtc2 mutant is qE. HL-grown plants exhibited less NPQ, except for the vtc2 mutant that still had the same high levels as when grown in LL (Fig. 3D).
Total Chl per leaf area was 30% lower in HL-grown plants compared with LL in all four genotypes, with the two double mutants having less Chl in LL and HL than the wild type (Fig. 4A). In addition, the Chl a to b ratio was higher in all genotypes when grown in HL, but the ascorbate-deficient mutants had lower Chl a to b ratios than the wild type (Fig. 4B).
The xanthophyll cycle pool size was the same for HL-grown genotypes, except for vtc2npq1, which had slightly lower values, and it was about three times higher than in LL-grown plants (Fig. 5A). On the other hand, all ascorbate-deficient mutants had a somewhat smaller xanthophyll cycle pool than the wild type when grown in LL. In LL, the xanthophyll cycle pool was not much de-epoxidized in any of the four genotypes ([A + Z]/[V + A + Z] < 0.045; data not shown). When grown in HL, the vtc2 mutant had 69% of its pool de-epoxidized (Fig. 5B). Both the vtc2npq4 mutant and the wild type had only 50% and 62% of their pools de-epoxidized, respectively. The vtc2npq1 mutant, because of its impairment in violaxanthin de-epoxidase, had less than 10% of its pool in an unepoxidized state.
Plants grown in HL showed the same degree of lipid peroxidation as did plants grown in LL (Fig. 6). Lipid peroxidation was measured as the amount of thiobarbituric acid-reactive substances (TBARS). The TBARS method has been shown to give a good estimate of lipid peroxidation and correlates well with other types of lipid peroxidation measurements, such as thermoluminescence (Müller-Moulé et al., 2003
To test if thylakoid protein complexes were affected in the ascorbate-deficient mutants, we tested levels of several proteins. Because photosynthetic function is dependent on Chl, we normalized protein levels based on Chl content. The photosynthetic electron transport chain is comprised of three major protein complexes: PSII, the cytochrome b6/f complex, and PSI. We wanted to test at least one protein of each complex to detect differences between LL- and HL-grown plants and between genotypes. The PSII reaction center protein D1 is known to be the primary target of photodamage (Aro et al., 1993
We also tested the activity of APX, which uses ascorbate to reduce hydrogen peroxide to water. APX is an important enzyme that is found in several compartments and replaces catalase in the chloroplast. Because there might be substrate limitation in the ascorbate-deficient mutants, we were interested to see if the ascorbate-deficient mutants were impaired in APX activity. However, there were no differences between the mutants in LL or HL, although the data were somewhat more variable in the HL-grown mutants (Fig. 8A).
2-CP is an important antioxidant enzyme that is found in the chloroplast and reduces lipid hydroperoxides (Baier and Dietz, 1999b
HL-grown plants had higher levels of antioxidants when compared with LL-grown plants. In the wild type, both ascorbate and
In LL and HL, the ascorbate content of the ascorbate-deficient mutants was only 5% to 10% and 35% to 39%, respectively, of the wild-type value (Fig. 9A). Thus, the ascorbate level of the mutants was 7- to 14-fold higher in HL than in LL, compared with approximately 2-fold higher levels in the wild type. The redox state of ascorbate (reduced ascorbate/total ascorbate) was not different between the wild type and the mutants in LL except for vtc2npq1, which had a lower ratio of 0.6 (Fig. 9B). In HL, both vtc2 and vtc2npq1 had a lower redox state than the wild type. The vtc2npq4 double mutant had a somewhat higher ascorbate level in LL and a slightly higher ascorbate redox state in HL than the other mutants. Total glutathione content was 30% higher in the ascorbate-deficient mutants when grown in HL (Fig. 9C), whereas there was no difference in the wild type. For all genotypes, there was a very small difference in the reduced to total glutathione ratio between LL- and HL-grown plants. When grown in HL, all four genotypes showed a slightly more oxidized pool (0.95 in HL versus 0.99 in LL).
In LL, the wild type and the vtc2npq4 had the same
Ascorbate-deficient mutants were able to grow to maturity at a PFD of 1,800 µmol photons m-2 s-1. No visible signs of damage were apparent at this HL intensity. The ascorbate-deficient mutants had similar levels of representative thylakoid proteins (Fig. 7) and did not bleach, produce anthocyanins, or show lipid peroxidation (Figs. 1 and 6), although they exhibited symptoms of photooxidative stress such as lower Fv/Fm (Fig. 2A), Pmax (Fig. 2B), and  PSII (Fig. 3B). The growth in HL was surprising because under standard LL conditions, the vtc2 mutants have been shown to have 10% to 25% of the wild-type ascorbate content (Conklin et al., 2000; Müller-Moulé et al., 2002). Because ascorbate is one of the major antioxidants in plant cells, one might have expected to see a more negative effect on growth in HL, maybe even lethality. Transfer of ascorbate-deficient mutants from LL to HL results in dramatic bleaching and lipid peroxidation (Müller-Moulé et al., 2003). When grown in HL, however, both the wild-type and the ascorbate-deficient mutants had higher ascorbate levels than in LL. In fact, the levels of ascorbate increased relatively more in the mutants than in the wild type, so that the HL-grown mutants had approximately 40% of the wild-type ascorbate levels (Fig. 9A). Thus, we conclude that an ascorbate content of 10% or 40% of the wild type is enough for Arabidopsis plants to survive when grown in LL or HL, respectively.
The relatively higher ascorbate content of the HL-grown mutants could be because of an increased ascorbate synthesis. The mutants exhibit lower Fv/Fm values in HL and might experience higher photooxidative stress than the wild type when grown in HL, which might cause a stronger acclimation response in regard to producing more antioxidants. The relatively higher ascorbate levels could also be because of developmental variation in ascorbate content in the mutants. For example, the ascorbate content of LL-grown vtc2 mutants decreases from 30% to 10% of wild-type levels in "mature" leaves between 2 and 6 weeks of age (Conklin et al., 2000
However, how is it possible that less than one-half the wild-type ascorbate levels is sufficient for growth in HL? One likely explanation is that the ascorbate-deficient plants compensated for the lack of ascorbate by increasing other photoprotective mechanisms or the level of other antioxidants. First of all, ascorbate-deficient mutants showed an increase in another water-soluble antioxidant, glutathione, which had 30% higher levels in HL than the wild type (Fig. 9C). The increase in glutathione provides evidence for overlap in the antioxidant functions of ascorbate and glutathione in vivo. In contrast, there were no differences in the levels of the lipid-soluble antioxidants, carotenoids (Figs. 4 and 5) and
Even though the ascorbate-deficient mutants were able to grow in HL, they did not show a full acclimation to it as compared with the wild type. There were signs of photooxidative stress and impairment of cell components when the mutants were grown in HL. Mutant plants, except vtc2npq4, had a more oxidized ascorbate pool when grown in HL. The vtc2npq4 mutant also had a higher total antioxidant content in HL than the vtc2 and vtc2npq1 mutants because of a higher
An increased need for dissipation of excess energy because of the lowered
It is somewhat surprising that the mutants did not have the same or even a higher Pmax and
It is also possible that there was incomplete acclimation to HL in the mutants because of a defect in a signaling pathway, which might involve ascorbate. Both the redox states of ascorbate and glutathione might play a role in signaling HL stress (Potters et al., 2002
In both light conditions, the ascorbate-deficient mutants had the same stomatal index as the wild type, fewer and thinner leaves with more cell layers, and a smaller rosette diameter than the wild type (Table I; Fig. 1). Because leaf thickening is a characteristic feature of HL acclimation in the wild type, it is possible that the failure of the mutants to make this morphological change contributed to the symptoms of photooxidative stress that were observed. In LL, however, the decreased growth of ascorbate-deficient mutants does not seem to be attributable to increased oxidative stress, because in previous studies vtc1 displayed slower shoot growth even in high CO2 where oxidative stress is minimized (Veljovic-Jovanovic et al., 2001
To summarize, we have shown that ascorbate-deficient mutants are able to grow in HL. This likely is because of compensation by other antioxidants and photoprotective mechanisms, when plants were grown in HL from seedling age on. The mutants had higher glutathione levels than the wild type and possibly other increased protective mechanisms not considered here. Also, the increased photosynthetic rate combined with the smaller antenna size might have lowered the amount of excess light plants were actually experiencing, thereby reducing the amount of ROS produced. When plants were transferred from LL to HL, ascorbate-deficient mutants showed a much higher sensitivity to HL (Müller-Moulé et al., 2003
Plant Material and Growth Conditions All genotypes used were of the Arabidopsis ecotype Columbia-0. The two double mutants were constructed by crossing a twice-backcrossed vtc2-1 with a four times-backcrossed npq1-2 (vtc2npq1) or with a four times-backcrossed npq4-1 (vtc2npq4). The double mutants were identified based on measurements of NPQ, ascorbate content, and lack of either zeaxanthin (vtc2npq1) or the PsbS protein (vtc2npq4). The plants were grown in a 10-h-light (20°C)/14-h-dark (18°C) cycle with a PFD of 180 µmol photons m-2 s-1 (LL) or a PFD of 1,800 µmol photons m-2 s-1 (HL) in the same growth chamber with high-intensity discharge lighting (E15, Conviron, Winnipeg, MN, Canada). Measurements were performed on rosette leaves from plants at the same developmental stage (before the induction of flowering), which corresponded to an age of 6 weeks for LL-grown plants and 4 weeks for HL-grown plants. Samples were taken 4 h into the light period except for the fluorescence measurements. Leaf temperature was 21.1°C ± 0.5°C in LL and 24.9°C ± 1.4°C in HL.
Standard modulated Chl fluorescence measurements (for review, see Maxwell and Johnson, 2000
A total of 12 samples (three independently grown sets of plants with four samples each) were measured by HPLC as previously described by Müller-Moulé et al. (2002
Total and reduced ascorbate were determined by a spectrophotometric method using the absorption at 265 nm by reduced ascorbate (Conklin et al., 1996
Glutathione was determined by HPLC followed by electrochemical detection (ESA Coularray, ESA Inc., Chelmsford, MA). Leaf disc samples (six total from two sets; HL-grown plants) or one set (LL-grown plants) were taken and immediately frozen in liquid nitrogen. The frozen discs were ground to a fine powder and extracted with 300 µL of 2% (w/v) metaphosphoric acid/2 mM EDTA, followed by 30 s of vortexing. The extract was centrifuged at 15,300g for 3 min, and 20 µL of the filtered supernatant was subjected to HPLC and separated on a TSK-GEL ODS-80Tm column (XXXX, XXXX, XX) at 30°C with a flow rate of 1 mL min-1 for 20 min. The mobile phase consisted of 0.2 M potassium phosphate (pH 3), 100 mg L-1 1-pentanesulfonic acid, and 1% (w/v) acetonitrile. The eight channels of the electrochemical detector were set at -200, -100, 0, +450, +50, +750, +880, and +900 mV. GSH was detected at +650 and +750 mV with +650 mV being the major channel. Oxidized glutathione was detected at +650, +750, and 880 mV with +750 mV being the major channel.
Lipid peroxidation was determined as the level of TBARS (Hodges et al., 1999
Oxygen evolution was measured in detached leaves with a leaf disc electrode system (LD2/2, Hansatech) in response to a series of increasing PFDs at saturating CO2. Seven leaf discs from different plants were used for each measurement for the LL-grown plants. For the HL-grown plants, seven whole leaves from different plants were used. For normalization of data for the HL-grown plants, leaf area was determined using the NIH Image program (National Institutes of Health, Bethesda, MD). The saturating PFD for oxygen evolution was determined for plants grow under each light condition by a light response curve, and the maximum rate of oxygen evolution was determined at a saturating PFD (1,380 µmol photons m-2 s-1 for LL-grown plants and 1,790 µmol photons m-2 s-1 for HL-grown plants). The measurements were repeated four to six times with plant samples from one set.
Leaves were harvested and frozen immediately in liquid nitrogen. Thylakoids were isolated from these leaves as described before (Li et al., 2002a
Two leaf discs were taken and immediately frozen in liquid nitrogen. The leaf discs were ground to a fine powder in 1.5 mL of extraction buffer using a mortar and pestle. A previously described APX assay was used (Grace and Logan, 1996
We thank Barry Logan for helping with the APX assay and Anastasios Melis, Andrew Staehelin, Stefan Jansson, Richard Malkin, Anna Haldrup, Margarete Baier, and Karl-Josef Dietz for providing antibodies. We also thank Xiao-Ping Li for critical reading of this manuscript. Received August 26, 2003; returned for revision September 29, 2003; accepted November 21, 2003.
Article, publication date, and citation information can be found at http://www.plantphysiol.org/cgi/doi/10.1104/pp.103.032375.
1 This work was supported by the U.S. Department of Agriculture National Research Initiative (grant no. 98-35306-6600) and by the Director, Office of Science, Office of Basic Energy Sciences, Chemical Sciences Division, of the U.S. Department of Energy (contract no. DE-AC03-765F00098). * Corresponding author; e-mail niyogi{at}nature.berkeley.edu; fax 510-642-4995.
Anderson JM, Osmond CB (1987) Shade-sun responses: compromises between acclimation and photoinhibition. In DJ Kyle, CB Osmond, CJ Arntzen, eds, Photoinhibition, Vol 9. Elsevier, Amsterdam, pp 1-38 Aro E-M, Virgin I, Andersson B (1993) Photoinhibition of photosystem II: inactivation, protein damage and turnover. Biochim Biophys Acta 1143: 113-134[Medline]
Baier M, Dietz K-J (1999a) Protective function of chloroplast 2-cysteine peroxiredoxin in photosynthesis: evidence from transgenic Arabidopsis. Plant Physiol 119: 1407-1414 Baier M, Dietz K-J (1999b) Alkyl hydroperoxide reductases: the way out of the oxidative breakdown of lipids in chloroplasts. Trends Plant Sci 4: 166-168[CrossRef][ISI][Medline]
Baroli I, Do AD, Yamane T, Niyogi KK (2003) Zeaxanthin accumulation in the absence of a functional xanthophyll cycle protects Chlamydomonas reinhardtii from photooxidative stress. Plant Cell 15: 992-1008 Björkman O (1981) Responses to different quantum flux densities. In O Lange, Nobel PS, Osmond CB, Ziegler H, eds, Physiological Plant Ecology I: Responses to the Physical Environment. Springer-Verlag, Berlin, pp 57-107 Brownlee C (2001) The long and short of stomatal density signals. Trends Plant Sci 6: 441-442[CrossRef][ISI][Medline]
Conklin PL, Saracco SA, Norris SR, Last RL (2000) Identification of ascorbic acid-deficient Arabidopsis thaliana mutants. Genetics 154: 847-856
Conklin PL, Williams EH, Last RL (1996) Environmental stress sensitivity of an ascorbic acid-deficient Arabidopsis mutant. Proc Natl Acad Sci USA 93: 9970-9974 De la Torre W, Burkey K (1990) Acclimation of barley to changes in light intensity: photosynthetic electron transport activity and components. Photosynth Res 24: 127-136[CrossRef]
Demmig B, Winter K, Krueger A, Czygan F-C (1987) Photoinhibition and zeaxanthin formation in intact leaves. Plant Physiol 84: 218-224
Demmig-Adams B, Winter K, Krueger A, Czygan F-C (1989) Light response of carbon dioxide assimilation dissipation of excess excitation energy and zeaxanthin content of sun and shade leaves. Plant Physiol 90: 881-886 Foyer C, Rowell J, Walker D (1983) Measurement of ascorbate content of spinach leaf protoplasts and chloroplasts during illumination. Planta 157: 239-244 Foyer CH (1997) Oxygen metabolism and electron transport in photosynthesis. In JG Scandalios, ed, Oxidative Stress and the Molecular Biology of Antioxidant Defenses. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, pp 587-621 Garcia-Ferris C, Moreno J (1994) Oxidative modification and breakdown of ribulose-1,5-bisphosphate carboxylase/oxygenase induced in Euglena gracilis by nitrogen starvation. Planta 193: 208-215 Grace SC, Logan BA (1996) Acclimation of foliar antioxidant systems to growth irradiance in three broad-leaved evergreen species. Plant Physiol 112: 1631-1640[Abstract] Gray JE, Holroyd GH, van der Lee FM, Bahrami AR, Sijmons PC, Woodward FI, Schuch W, Hetherington AM (2000) The HIC signalling pathway links CO2 perception to stomatal development. Nature 408: 713-716[CrossRef][Medline] Hager A (1969) Lichtbedingte pH-erniedrung in einem chloroplasten-kompartiment als ursache der enzymatischen violaxanthin-zeaxanthin-umwandlung; beziehung zur photophosphorylierung. Planta 89: 224-243[CrossRef]
Havaux M, Niyogi KK (1999) The violaxanthin cycle protects plants from photooxidative damage by more than one mechanism. Proc Natl Acad Sci USA 96: 8762-8767 Hodges DM, DeLong JM, Forney CF, Prange RK (1999) Improving the thiobarbituric acid-reactive-substances assay for estimating lipid peroxidation in plant tissues containing anthocyanin and other interfering compounds. Planta 207: 604-611[CrossRef]
Jander G, Norris SR, Rounsley SD, Bush DF, Levin IM, Last RL (2002) Arabidopsis map-based cloning in the post-genome era. Plant Physiol 129: 440-450 Kaiser W (1979) Reversible inhibition of the Calvin cycle and activation of oxidative pentose phosphate cycle in isolated chloroplasts by hydrogen peroxide. Planta 145: 377-382[CrossRef] Li X-P, Björkman O, Shih C, Grossman AR, Rosenquist M, Jansson S, Niyogi KK (2000) A pigment-binding protein essential for regulation of photosynthetic light harvesting. Nature 403: 391-395[CrossRef][Medline]
Li X-P, Müller-Moulé P, Gilmore AM, Niyogi KK (2002b) PsbS-dependent enhancement of feedback de-excitation protects photosystem II from photoinhibition. Proc Natl Acad Sci USA 99: 15222-15227 Li X-P, Phippard A, Pasari J, Niyogi KK (2002a) Structure-function analysis of photosystem II subunit S (PsbS) in vivo. Funct Plant Biol 29: 1131-1139[CrossRef]
Lukowitz W, Nickle TC, Meinke DW, Last RL, Conklin PL, Somerville CR (2001) Arabidopsis cyt1 mutants are deficient in a mannose-1-phosphate guanylyltransferase and point to a requirement of N-linked glycosylation for cellulose biosynthesis. Proc Natl Acad Sci USA 98: 2262-2267
Maxwell K, Johnson GN (2000) Chlorophyll fluorescence: a practical guide. J Exp Bot 51: 659-668
Mehta RA, Fawcett TW, Porath D, Mattoo AK (1992) Oxidative stress causes rapid membrane translocation and in-vivo degradation of ribulose-1,5-bisphosphate carboxylase-oxygenase. J Biol Chem 267: 2810-2816
Müller P, Li X-P, Niyogi KK (2001) Non-photochemical quenching: a response to excess light energy. Plant Physiol 125: 1558-1566
Müller-Moulé P, Conklin PL, Niyogi KK (2002) Ascorbate deficiency can limit violaxanthin de-epoxidase activity in vivo. Plant Physiol 128: 970-977
Müller-Moulé P, Havaux M, Niyogi KK (2003) Zeaxanthin deficiency enhances the high light sensitivity of an ascorbate-deficient mutant of Arabidopsis. Plant Physiol 133: 748-760 Niyogi KK (1999) Photoprotection revisited: genetic and molecular approaches. Annu Rev Plant Physiol Plant Mol Biol 50: 333-359[CrossRef][ISI]
Niyogi KK, Björkman O, Grossman AR (1997) The roles of specific xanthophylls in photoprotection. Proc Natl Acad Sci USA 94: 14162-14167
Niyogi KK, Grossman AR, Björkman O (1998) Arabidopsis mutants define a central role for the xanthophyll cycle in the regulation of photosynthetic energy conversion. Plant Cell 10: 1121-1134 Niyogi KK, Shih C, Chow WS, Pgoson BJ, DellaPenna D, Björkman O (2001) Photoprotection in a zeaxanthin- and lutein-deficient double mutant of Arabidopsis. Photosynth Res 67: 139-145[CrossRef][ISI][Medline] Noctor G, Veljovic-Jovanovic S, Foyer CH (2000) Peroxide processing in photosynthesis: antioxidant coupling and redox signalling. Philos Trans R Soc Lond B Biol Sci 355: 1465-1475[Medline]
Pastori GM, Kiddle G, Antoniw J, Bernard S, Veljvic-Jovanovic S, Verrier PJ, Noctor G, Foyer CH (2003) Leaf vitamin C contents modulate plant defense transcripts and regulate genes that control development through hormone signaling. Plant Cell 15: 939-951 Pearcy RW (1998) Acclimation to sun and shade. In A Raghavendra, ed, Photosynthesis. Cambridge University Press, Cambridge, UK Potters G, De Gara L, Asard H, Horemans N (2002) Ascorbate and glutathione: guardians of the cell cycle, partners in crime? Plant Physiol Biochem 40: 537-548[CrossRef][ISI]
Rossel JB, Wilson IW, Pogson BJ (2002) Global changes in gene expression in response to high light in Arabidopsis. Plant Physiol 130: 1109-1120
Shikanai T, Munekage Y, Shimizu K, Endo T, Hashimoto T (1999) Identification and characterization of Arabidopsis mutants with reduced quenching of chlorophyll fluorescence. Plant Cell Physiol 40: 1134-1142 Smirnoff N (2000a) Ascorbic acid: metabolism and functions of a multi-facetted molecule. Curr Opin Plant Biol 3: 229-235[ISI][Medline] Smirnoff N (2000b) Ascorbate biosynthesis and function in photoprotection. Philos Trans R Soc Lond B Biol Sci 355: 1455-1464[CrossRef][ISI][Medline]
Veljovic-Jovanovic SD, Pignocchi C, Noctor G, Foyer CH (2001) Low ascorbic acid in the vtc-1 mutant of Arabidopsis is associated with decreased growth and intracellular redistribution of the antioxidant system. Plant Physiol 127: 426-435 Walters RG, Horton P (1994) Acclimation of Arabidopsis thaliana to the light environment: changes in composition of the photosynthetic apparatus. Planta 195: 248-256 This article has been cited by other articles:
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-tocopherol (vitamin E) and carotenoids, which are in the chloroplast membranes. Zeaxanthin and lutein have been shown through mutant studies in Arabidopsis and Chlamydomonas reinhardtii to be involved in the protection of the photosynthetic membrane (Niyogi et al., 1997
-Carotene levels were also lower in HL-grown plants when compared with LL-grown plants, except for the vtc2npq1 mutant, in which there were no differences (
