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1.
Photosynthesis, photosystem II (PSII) photochemistry, photoinhibition and the xanthophyll cycle in the senescent flag leaves of wheat (Triticum aestivum L.) plants grown in the field were investigated. Compared to the non-senescent leaves, photosynthetic capacity was significantly reduced in senescent flag leaves. The light intensity at which photosynthesis was saturated also declined significantly. The light response curves of PSII photochemistry indicate that a down-regulation of PSII photochemistry occurred in senescent leaves in particular at high light. The maximal efficiency of PSII photochemistry in senescent flag leaves decreased slightly when measured at predawn but substantially at midday, suggesting that PSII function was largely maintained and photoinhibition occurred in senescent leaves when exposed to high light. At midday, PSII efficiency, photochemical quenching and the efficiency of excitation capture by open PSII centers decreased considerably, while non-photochemical quenching increased significantly. Moreover, compared with the values at early morning, a greater decrease in CO2 assimilation rate was observed at midday in senescent leaves than in control leaves. The levels of antheraxanthin and zeaxanthin via the de-epoxidation of violaxanthin increased in senescent flag leaves from predawn to midday. An increase in the xanthophyll cycle pigments relative to chlorophyll was observed in senescent flag leaves. The results suggest that the xanthophyll cycle was activated in senescent leaves due to the decrease in CO2 assimilation capacity and the light intensity for saturation of photosynthesis and that the enhanced formation of antheraxanthin and zeaxanthin at high light may play an important role in the dissipation of excess light energy and help to protect photosynthetic apparatus from photodamage. Our results suggest that the well-known function of the xanthophyll cycle to safely dissipate excess excitation energy is also important for maintaining photosynthetic function during leaf senescence.  相似文献   

2.
Photosynthetic pigment composition and photosystem II (PSII) photochemistry were characterized during the flag leaf senescence of wheat plants grown in the field. During leaf senescence, neoxanthin and beta-carotene decreased concomitantly with chlorophyll, whereas lutein and xanthophyll cycle pigments were less affected, leading to increases in lutein/chlorophyll and xanthophyll cycle pigments/chlorophyll ratios. The chlorophyll a/b ratio also increased. With the progression of senescence, the maximal efficiency of PSII photochemistry decreased only slightly in the early morning (low light conditions), but substantially at midday (high light conditions). Actual PSII efficiency, photochemical quenching and the efficiency of excitation capture by open PSII centres decreased significantly both early in the morning and at midday and such decreases were much greater at midday than in the early morning. At the same time, non-photochemical quenching, zeaxanthin and antheraxanthin contents at the expense of violaxanthin increased both early in the morning and at midday, with a greater increase at midday. The results in the present study suggest that a down-regulation of PSII occurred in senescent leaves and that the xanthophyll cycle plays a role in the protection of PSII from photoinhibitory damage in senescent leaves by dissipating excess excitation energy, particularly when exposed to high light.  相似文献   

3.
The characteristics of pigment composition and photosystem II (PSII) photochemistry in the flag leaf and ear parts of wheat (Triticum aestivum L.) grown in the field was compared. At the early stage of flowering, awns and the flag leaf showed the highest values in the maximal efficiency of PSII photochemistry (Fv/Fm), actual PSII efficiency (phi(PSII)), photochemical quenching (qP), and the efficiency of excitation capture by open PSII centres (Fv/F'm), followed by glumes, lemmas, and paleae, respectively except that no differences in F'v/F'm were observed among glumes, leamms, and paleae. With progressing grain filling, there was a change in the photosynthetic pigment stoichiometry. In the ear parts, neoxanthin and antheraxanthin decreased equally with chlorophyll levels. Lutein and zeaxanthin decreased less than chlorophyll levels while beta-carotene and violaxanthin decreased faster than chlorophyll levels. No big differences in pigment composition were observed among different ear parts. For the flag leaf, neoxanthin and beta-carotene decreased concomitantly with chlorophyll, whereas lutein and xanthophyll cycle pigment were less affected, leading to increases in lutein/chlorophyll and xanthophyll cycle pigment/chlorophyll ratios. Fv/Fm, phi(PSII), qP, and F'v/F'm decreased gradually in the flag leaf and ear parts but to different extents. The largest changes were observed in awns, followed by the lemmas of floret 2, the lemmas of floret 1, glumes, and the flag leaf, respectively. The results suggest that during grain filling, a down-regulation of PSII associated with an increase of the de-epoxidation state of the xanthophyll cycle carotenoids occurred in the flag leaf but not in the ear parts.  相似文献   

4.
The objective of this study was to determine xanthophyll cycle pool size and composition in response to N status and their relationships to non-photochemical quenching in apple leaves. Bench-grafted Fuji/M.26 trees were fertilized with different N concentrations (0-20 mM) in a modified Hoagland's solution for 6 weeks to create a wide range of leaf N status (1-4.4 g m(-2)). Chlorophyll content, xanthophyll cycle pool size, lutein, total carotene, and neoxanthin on a leaf area basis all increased linearly with increasing leaf N. However, only the ratios of the xanthophyll cycle pool and of lutein to chlorophyll were higher in low N leaves than in high N leaves. Under high light at midday, both zeaxanthin (Z), expressed on a chlorophyll basis, and the percentage of the xanthophyll cycle pool present as Z, increased as leaf N decreased. Thermal dissipation of excitation energy, measured as non-photochemical quenching of chlorophyll fluorescence, was positively related to, whereas efficiency of excitation transfer and photosystem II quantum efficiency were negatively related to, Z, expressed on a chlorophyll basis or on a xanthophyll cycle pool basis. It is concluded that both xanthophyll cycle pool size (on a chlorophyll basis) and conversion of violaxanthin to zeaxanthin are enhanced in response to N limitation to dissipate excessive absorbed light under high irradiance.  相似文献   

5.
One-year-old grapevines (Vitis labrusca L. cv. Concord) were supplied with 0, 5, 10, 15, or 20 mM nitrogen (N) in a modified Hoagland's solution twice weekly for 4 weeks. As leaf N decreased in response to N limitation, leaf chlorophyll (Chl) decreased linearly whereas leaf absorptance declined curvilinearly. Compared with high N leaves, low N leaves had lower quantum efficiency of PSII as a result of both an increase in non-photochemical quenching (NPQ) and an increase in closure of PSII reaction centres at midday under high photon flux density (PFD). Both the xanthophyll cycle pool size on a Chl basis and the conversion of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) at noon increased with decreasing leaf N. NPQ was closely related to A+Z expressed either on a Chl basis or as a percentage of the xanthophyll cycle pool. As leaf N increased, superoxide dismutase (SOD) activity on a Chl basis decreased linearly; activities of catalase (CAT) and glutathione reductase (GR) on a Chl basis increased linearly; activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR) and dehydroascorbate reductase (DHAR) expressed on the basis of Chl decreased rapidly first, then gradually reached a low level. In response to N limitation, the contents of ascorbate (AsA), dehydroascorbate (DAsA), reduced glutathione (GSH), and oxidized glutathione (GSSG) increased when expressed on a Chl basis, whereas the ratios of both AsA to DAsA and GSH to GSSG decreased. It is concluded that, in addition to decreasing light absorption by lowering Chl concentration, both xanthophyll cycle-dependent thermal energy dissipation and the antioxidant system are up-regulated to protect low N leaves from photo-oxidative damage under high light.  相似文献   

6.
The possible role of zeaxanthin formation and antenna proteins in energy-dependent chlorophyll fluorescence quenching (qE) has been investigated. Intermittent-light-grown pea (Pisum sativum L.) plants that lack most of the chlorophyll a/b antenna proteins exhibited a significantly reduced qE upon illumination with respect to control plants. On the other hand, the violaxanthin content related to the number of reaction centers and to xanthophyll cycle activity, i.e. the conversion of violaxanthin into zeaxanthin, was found to be increased in the antenna-protein-depleted plants. Western blot analyses indicated that, with the exception of CP 26, the content of all chlorophyll a/b-binding proteins in these plants is reduced to less than 10% of control values. The results indicate that chlorophyll a/b-binding antenna proteins are involved in the energy-dependent fluorescence quenching but that only a part of qE can be attributed to quenching by chlorophyll a/b-binding proteins. It seems very unlikely that xanthophylls are exclusively responsible for the qE mechanism.Abbreviations CAB chlorophyll a/b-binding - Chl chlorophyll - FV variable fluorescence - IML intermittent light - LHC light harvesting complex - PFD photon flux density - qP photochemical quenching of chlorophyll fluoresence - qN non-photochemical quenching - qE energy-dependent quenching - qI photoinhibitory quenching - qT quenching by state transition  相似文献   

7.
Modulation of the efficiency with which leaves convert absorbed light to photochemical energy [intrinsic efficiency of open photosystem II (PSII) centers, as the ratio of variable to maximal chlorophyll fluorescence] as well as leaf xanthophyll composition (interconversions of the xanthophyll cycle pigments violaxanthin and zeaxanthin) were characterized throughout single days and nights to entire seasons in plants growing naturally in contrasting light and temperature environments. All pronounced decreases of intrinsic PSII efficiency took place in the presence of zeaxanthin. The reversibility of these PSII efficiency changes varied widely, ranging from reversible-within-seconds (in a vine experiencing multiple sunflecks under a eucalypt canopy) to apparently permanently locked-in for entire seasons (throughout the whole winter in a subalpine conifer forest at 3,000?m). While close association between low intrinsic PSII efficiency and zeaxanthin accumulation was ubiquitous, accompanying features (such as trans-thylakoid pH gradient, thylakoid protein composition, and phosphorylation) differed among contrasting conditions. The strongest and longest-lasting depressions in intrinsic PSII efficiency were seen in the most stress-tolerant species. Evergreens, in particular, showed the most pronounced modulation of PSII efficiency and thermal dissipation, and are therefore suggested as model species for the study of photoprotection. Implications of the responses of field-grown plants in nature for mechanistic models are discussed.  相似文献   

8.
田间大豆叶片成长过程中的光合特性及光破坏防御机制   总被引:9,自引:0,他引:9  
田间大豆叶片在成长进程中光饱和光合速率持续提高,但气孔导度的增加明显滞后.尽管叶片在成长初期就具有较高的最大光化学效率,但是仍略低于发育成熟的叶片.随着叶片的成长,光下叶片光系统Ⅱ实际效率增加;非光化学猝灭下降.幼叶叶黄素总量与叶绿素之比较高,随着叶面积的增加该比值下降,在光下,幼叶的脱环氧化程度较高.因此认为大豆叶片成长初期就能够有效地进行光化学调节;在叶片生长过程中依赖叶黄素循环的热耗散机制迅速建立起来有效抵御强光的破坏.  相似文献   

9.
Physiological and photosynthetic responses were investigated at three different depths of groundwater (DGW: 1.4, 2.4, and 3.4 m) in Elaeagnus angustifolia L., a locally adapted tree to the arid region in northwest China. Predawn leaf water potential and chlorophyll content declined gradually with the increasing DGW, whereas there was little effect on predawn variable-to-maximum chlorophyll fluorescence ratio F v/F m and leaf carotenoid compositions (xanthophyll cycle pool, neoxanthin, lutein, and β-carotene). Net photosynthetic rate (P n), quantum yield of PSII electron transport (ΦPSII), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) declined obviously; however, P n decreased more than ΦPSII at deeper DGW. The photoinhibition of PSII at all three DGW occurred at midday in summer and increased as DGW increased. The ΔpH-dependent thermal dissipation and the level of de-epoxidation of the xanthophyll cycle at all three DGW reached their maxima at midday with the increase of light intensity. However, the fraction of functional PSII and light intensity at deeper DGW (2.4, 3.4 m) showed a negative correlation. This correlation suggested that most of violaxanthin was converted into zeaxanthin at midday, and the reversible inactivation of partial PSII reaction centers took place at deeper DGW. These results together suggest that both the xanthophyll cycle-dependent thermal dissipation and the reversible inactivation of partial PSII might have played important roles in avoiding the excess light-induced energy damage in leaves of this tree species at deeper DGW.  相似文献   

10.
Posters Part 1     
Schima superba and Pinus massoniana distributed over large areas in southern China both are dominant species at Dinghushan Biosphere Reserve. In the present study, the changes of chlorophyll fluorescence and xanthophyll cycle in the leaves of S. superba and P. massoniana exposed to simulated acid rain (SAR) were measured. When exposed to high light, the PSII photochemistry efficiency (F v/F m), efficiency of energy conversion in PSII (ΦPSII) and photochemical quenching (qP) of both S. superba and P. massoniana all decreased when acidity of SAR increased. Regarding non-photochemical quenching (qN), S. superba exposed to SAR had higher value than control plants, but there was no significant difference between the respective seedlings of P. massoniana. As for xanthophyll cycle of the two plant species, the leaves of S. superba exposed to SAR showed a higher content of carotenoids and a higher ability to convert violaxanthin to zeaxanthin than leaves of P. massoniana, which was consistent with S. superba exhibiting a stronger resistance to high light than P. massoniana. Although both species were susceptible to acid rain as shown by our results, P. massoniana was more susceptible compared to S. superba. These results provide an insight into how to protect the forest ecosystem at Dinghushan Biosphere Reserve.  相似文献   

11.
The response of Norway spruce saplings (Picea abies [L.] Karst.) was monitored continuously during short-term exposure (10 days) to high irradiance (HI; 1000mumolm(-2)s(-1)). Compared with plants acclimated to low irradiance (100mumolm(-2)s(-1)), plants after HI exposure were characterized by a significantly reduced CO(2) assimilation rate throughout the light response curve. Pigment contents varied only slightly during HI exposure, but a rapid and strong response was observed in xanthophyll cycle activity, particularly within the first 3 days of the HI treatment. Both violaxanthin convertibility under HI and the amount of zeaxanthin pool sustained in darkness increased markedly under HI conditions. These changes were accompanied by an enhanced non-radiative dissipation of absorbed light energy (NRD) and the acceleration of induction of both NRD and de-epoxidation of the xanthophyll cycle pigments. We found a strong negative linear correlation between the amount of sustained de-epoxidized xanthophylls and the photosystem II (PSII) photochemical efficiency (F(V)/F(M)), indicating photoprotective down-regulation of the PSII function. Recovery of F(V)/F(M) at the end of the HI treatment revealed that Norway spruce was able to cope with a 10-fold elevated irradiance due particularly to an efficient NRD within the PSII antenna that was associated with enhanced violaxanthin convertibility and a light-induced accumulation of zeaxanthin that persisted in darkness.  相似文献   

12.
The dark-adapted Photosystem II efficiency of field-grown pear leaves, estimated by the variable to maximum chlorophyll fluorescence ratio, was little affected by moderate and severe iron deficiency. Only extremely iron-deficient leaves showed a decreased Photosystem II efficiency after dark adaptation. Midday depressions in Photosystem II efficiency were still found after short-term dark-adaptation in iron-deficient leaves, indicating that Photosystem II down-regulation occurred when the leaves were illuminated by excessive irradiance. The actual Photosystem II efficiency at steady-state photosynthesis was decreased by iron deficiency both early in the morning and at midday, due to closure of Photosystem II reaction centers and decreases of the intrinsic Photosystem II efficiency. Iron deficiency decreased the amount of light in excess of that which can be used in photosynthesis not only by decreasing absorptance, but also by increasing the relative amount of light dissipated thermally by the Photosystem II antenna. When compared to the controls, iron-deficient pear leaves dissipated thermally up to 20% more of the light absorbed by the Photosystem II, both early in the morning and at midday. At low light iron-deficient leaves with high violaxanthin cycle pigments to chlorophyll ratios had increases in pigment de-epoxidation, non-photochemical quenching and thermal dissipation. Our data suggest that pH could be the major factor controlling thermal energy dissipation, and that large (more than 10-fold) changes in the zeaxanthin plus antheraxanthin to chlorophyll molar ratio caused by iron deficiency were associated only to moderate increases in the extent of photoprotection.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

13.
Post-anthesis leaf senescence is a key developmental process in the life of plants as it is the time during which material built up by the plant during its growth phase is mobilized into reproductive tissues. Here we aimed to study the extent of photo- and antioxidant protection and salicylic acid (SA) accumulation during post-anthesis leaf senescence in a perennial plant, Salvia lanigera Poir. grown under Mediterranean field conditions. SA levels increased sharply (up to 2.7-fold) during early stages of leaf senescence until fruit and seed formation occurred (i.e. 4 weeks after anthesis). Later on, SA levels kept at constant high levels until leaf abscission occurred (i.e. 7 weeks after anthesis). Reductions in chlorophyll and carotenoid (lutein, violaxanthin and β-carotene) levels occurred progressively during leaf senescence. In contrast, xanthophyll cycle de-epoxidation increased during early stages of leaf senescence and remained constant later, similar to SA accumulation. Indeed, xanthophyll cycle de-epoxidation strongly positively correlated with SA levels (r2 = 0.92). The maximum efficiency of PSII (Fv/Fm ratio) kept around 0.80 throughout the experiment, except during the latest stage of leaf senescence (i.e. after fruit and seed formation), when this ratio decreased to 0.72, thus indicating damage to PSII. It is concluded that endogenous SA levels increase sharply during early stages of post-anthesis leaf senescence and concomitantly with activation of photoprotection mechanisms, such as xanthophyll cycle-dependent excess energy dissipation, thus avoiding damage to PSII until fruit and seed formation have been accomplished.  相似文献   

14.
The effects of high salinity (0-400 mmol/L NaCl) on photosystem II (PSII) photochemistry and photosynthetic pigment composition were investigated in the halophyte Artimisia anethifolia grown under outdoor conditions and exposed to full sunlight. High salinity resulted in an inhibition in plant growth and a significant accumulation of sodium and chloride in leaves. However, high salinity induced no effects on the actual PSII efficiency, the efficiency of excitation energy capture by open PSII reaction centres, photochemical quenching, and non-photochemical quenching at midday. High salinity also induced neither changes in the maximum efficiency of PSII photochemistry, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than QA and the quantum yield of electron transport beyond QA, nor changes in absorption, trapping and electron transport fluxes per PSII reaction centre. No significant changes were observed in the levels of neoxanthin, lutein, beta-carotene, violaxanthin, antheraxanthin, and zeaxanthin expressed on a total chlorophyll basis in salt-adapted plants. Our results suggest that Artimisia anethifolia showed high resistance not only to high salinity, but also to photoinhibition even if it was treated with high salinity as high as 400 mmol/L NaCl and exposed to full sunlight. The results indicate that tolerance of PSII to high salinity and photoinhibition can be viewed as an important strategy for Artimisia anethifolia, a halophyte plant, to grow in very high saline soil.  相似文献   

15.
The temperature dependence of the rate of de-epoxidation of violaxanthin to zeaxanthin was determined in leaves of chilling-sensitive Gossypium hirsutum L. (cotton) and chilling-resistant Malva parviflora L. by measurements of the increase in absorbance at 505 nm (A 505) and in the contents of antheraxanthin and zeaxanthin that occur upon exposure of predarkened leaves to excessive light. A linear relationship between A 505 and the decrease in the epoxidation state of the xanthophyll-cycle pigment pool was obtained over the range 10–40° C. The maximal rate of de-epoxidation was strongly temperature dependent; Q10 measured around the temperature at which the leaf had developed was 2.1–2.3 in both species. In field-grown Malva the rate of de-epoxidation at any given measurement temperature was two to three times higher in leaves developed at a relatively low temperature in the early spring than in those developed in summer. Q10 measured around 15° C was in the range 2.2–2.6 in both kinds of Malva leaves, whereas it was as high as 4.6 in cotton leaves developed at a daytime temperature of 30° C. Whereas the maximum (initial) rate of de-epoxidation showed a strong decrease with decreased temperature the degree of de-epoxidation reached in cotton leaves after a 1–2 · h exposure to a constant photon flux density increased with decreased temperature as the rate of photosynthesis decrease. The zeaxanthin content rose from 2 mmol · (mol chlorophyll)–1 at 30° C to 61 mmol · (mol Chl)–1 at 10° C, corresponding to a de-epoxidation of 70% of the violaxanthin pool at 10° C. The degree of de-epoxidation at each temperature was clearly related to the amount of excessive light present at that temperature. The relationship between non-photochemical quenching of chlorophyll fluorescence and zeaxanthin formation at different temperatures was determined for both untreated control leaves and for leaves in which zeaxanthin formation was prevented by dithiothreitol treatment. The rate of development of that portion of non-photochemical quenching which was inhibited by dithiothreitol decreased with decreasing temperature and was linearly related to the rate of zeaxanthin formation over a wide temperature range. In contrast, the rate of development of the dithiothreitol-resistant portion of non-photochemical quenching was remarkably little affected by temperature. Evidently, the kinetics of the development of non-photochemical quenching upon exposure of leaves to excessive light is therefore in large part determined by the rate of zeaxanthin formation. For reasons that remain to be determined the relaxation of dithiothreitolsensitive quenching that is normally observed upon darkening of illuminated leaves was strongly inhibited at low temperatures.Abbreviations and Symbols Chl chlorophyll - DTT dithiothreitol - EPS epoxidation state - NPQ non-photochemical chlorophyll fluorescence quenching - PFD photon flux density - PSII photosystem II - F, Fm fluorescence emission at the actual, full closure of the PSII centers C.I.W.-D.P.B. Publication No. 1092We thank Connie Shih for skillful assistance in growing the plants, for conducting the HPLC analyses, and for preparing the figures. A Carnegie Institution Fellowship and a Feodor-Lynen-Fellowship by the Alexander von Humboldt-Foundation to W.B. is gratefully acknowledged. This work was supported by Grant No. 89-37-280-4902 of the Competitive Grants Program of the U.S. Department of Agriculture to O.B.  相似文献   

16.
Upon termination of watering of plants of Nerium oleander exposed to high light, photochemical efficiency became reduced as leaf water content decreased. Evidence is presented that this type of photoinhibition reflects to a substantial degree radiationless dissipation of excitation energy, probably mediated by the carotenoid zeaxanthin. During the imposition of water stress, the zeaxanthin content of leaves increased at the expense of violaxanthin and β-carotene as a water deficit developed over a period of several days. The increase in zeaxanthin content was linearly related to an increase in the rate of radiationless energy dissipation in the antenna chlorophyll as calculated from the characteristics of chlorophyll a fluorescence measured with a pulse amplitude modulated fluorometer at room temperature. The increase in the rate of radiationless dissipation was also linearly related to a decrease in PSII photochemical efficiency as indicated by the ratio of variable to maximum fluorescence. Leaves of well-watered shade plants of N. oleander exposed to strong light showed a similar increase in zeaxanthin content as sun leaves of the same species subjected to drought in strong light. Shade leaves possessed the same capacity as sun leaves to form zeaxanthin at the expense of both violaxanthin and β-carotene. The resistance of this species to the destructive effects of excess light appears to be related to interconversions between β-carotene and the three carotenoids of the xanthophyll cycle.  相似文献   

17.
Attached intact leaves of Schefflera arboricola grown at three different photon flux densities (PFDs) were subjected to 24-h exposures to a high PFD and subsequent recovery at a low PFD. While sun leaves showed virtually no sustained effects on photosystem II (PSII), shade-grown leaves exhibited pronounced photoinhibition of PSII that required several days at low PFD to recover. Upon transfer to high PFD, levels of nonphotochemical quenching in PSII as well as levels of zeaxanthin were initially low in shade leaves but continued to increase gradually during the 24-h exposure. The xanthophyll cycle pool size rose gradually during and also subsequent to the photoinhibitory treatment in shade leaves. Upon return to low PFD, a marked and extremely long-lasting retention of zeaxanthin and antheraxanthin was observed in shade but not sun leaves. During recovery, changes in the conversion state of the xanthophyll cycle therefore closely mirrored the slow increases in PSII efficiency. This novel report of a close association between zeaxanthin retention and lasting PSII depressions in these shade leaves clearly suggests a role for zeaxanthin in photoinhibition of shade leaves. In addition, there was a decrease in β-carotene levels, some decrease in chlorophyll, but no change in lutein and neoxanthin (all per leaf area) in the shade leaves during and subsequent to the photoinhibitory treatment. These data may be consistent with a degradation of a portion of core complexes but not of peripheral light-harvesting complexes. A possible conversion of β-carotene to form additional zeaxanthin is discussed. Received: 24 October 1997 / Accepted: 12 November 1997  相似文献   

18.
Conifers of the boreal zone encounter considerable combined stress of low temperature and high light during winter, when photosynthetic consumption of excitation energy is blocked. In the evergreen Pinus sylvestris L. these stresses coincided with major seasonal changes in photosystem II (PSII) organisation and pigment composition. The earliest changes occurred in September, before any freezing stress, with initial losses of chlorophyll, the D1-protein of the PSII reaction centre and of PSII light-harvesting-complex (LHC II) proteins. In October there was a transient increase in F0, resulting from detachment of the light-harvesting antennae as reaction centres lost D1. The D1-protein content eventually decreased to 90%, reaching a minimum by December, but PSII photochemical efficiency [variable fluorescence (Fv)/maximum fluorescence (Fm)] did not reach the winter minimum until mid-February. The carotenoid composition varied seasonally with a twofold increase in lutein and the carotenoids of the xanthophyll cycle during winter, while the epoxidation state of the xanthophylls decreased from 0.9 to 0.1 from October to January. The loss of chlorophyll was complete by October and during winter much of the remaining chlorophyll was reorganised in aggregates of specific polypeptide composition, which apparently efficiently quench excitation energy through non-radiative dissipation. The timing of the autumn and winter changes indicated that xanthophyll de-epoxidation correlates with winter quenching of chlorophyll fluorescence while the drop in photochemical efficiency relates more to loss of D1-protein. In April and May recovery of the photochemistry of PSII, protein synthesis, pigment rearrangements and zeaxanthin epoxidation occurred concomitantly. Indoor recovery of photosynthesis in winter-stressed branches under favourable conditions was completed within 3 d, with rapid increases in F0, the epoxidation state of the xanthophylls and in light-harvesting polypeptides, followed by recovery of D1-protein content and Fv/Fm, all without net increase in chlorophyll. The fall and winter reorganisation allow Pinus sylvestris to maintain a large stock of chlorophyll in a quenched, photoprotected state, allowing rapid recovery of photosynthesis in spring.Abbreviations Elips early light-induced proteins - EPS epoxidation state - F0 instantaneous fluorescence - Fm maximum fluorescence - Fv variable fluorescence - LHC II light-harvesting complex of PSII - LiDS lithium dodecyl sulfate This research was supported by the Swedish Natural Science Research Council. We wish to thank Dr. Adrian Clarke1 (Department of Plant Physiology, University of Umeå, Sweden) for advice on electrophoresis, valuable discussion and providing antibodies. Dr. Stefan Jansson1 and Dr. Torill Hundal (Department for Biochemistry, University of Stockholm, Sweden) provided antibodies. Jan Karlsson1 helped with the HPLC, Dr. Marianna Krol gave advice on green gels and Dr. Vaughan Hurry (Cooperative Research Centre for Plant Sciences, Australian National University, Canberra, Australia) provided valuable discussion.  相似文献   

19.
The relationships among the leaf adenylate energy charge, the xanthophyll-cycle components, and photosystem II (PSII) fluorescence quenching were determined in leaves of cotton (Gossypium hirsutum L. cv. Acala) under different leaf temperatures and different intercellular CO2 concentrations (Ci). Attenuating the rate of photosynthesis by lowering the Ci at a given temperature and photon flux density increased the concentration of high-energy adenylate phosphate bonds (adenylate energy charge) in the cell by restricting ATP consumption (A.M. Gilmore, O. Björkman 1994, Planta 192, 526–536). In this study we show that decreases in photosynthesis and increases in the adenylate energy charge at steady state were both correlated with decreases in PSII photo-chemical efficiency as determined by chlorophyll fluorescence analysis. Attenuating photosynthesis by decreasing Ci also stimulated violaxanthin-de-epoxidation-dependent nonradiative dissipation (NRD) of excess energy in PSII, measured by nonphotochemical fluorescence quenching. However, high NRD levels, which indicate a large trans-thylakoid proton gradient, were not dependent on a high adenylate energy charge, especially at low temperatures. Moreover, dithiothreitol at concentrations sufficient to fully inhibit violaxanthin de-epoxidation and strongly inhibit NRD, affected neither the increased adenylate energy charge nor the decreased PSII photo-chemical efficiency that result from inhibiting photosynthesis. The build-up of a high adenylate energy charge in the light that took place at low Ci and low temperatures was accompanied by a slowing of the relaxation of non-photochemical fluorescence quenching after darkening. This slowly relaxing component of nonphotochemical quenching was also correlated with a sustained high adenylate energy charge in the dark. These results indicate that hydrolysis of ATP that accumulated in the light may acidify the lumen and thus sustain the level of NRD for extended periods after darkening the leaf. Hence, sustained nonphotochemical quenching often observed in leaves subjected to stress, rather than being indicative of photoinhibitory damage, apparently reflects the continued operation of NRD, a photoprotective process.Abbreviations A antheraxanthin - adenylate kinase (myokinase), ATP:AMPphosphotransferase - Ci intercellular CO2 concentration - DPS de-epoxidation state of violaxanthin, ([Z+A]/[V+A+Z]) - DTT dithiothreitol - pH trans-thylakoid proton gradient - [2ATP+ADP] - F steady-state fluorescence in the presence of NRD - FM maximal fluorescence in the absence of NRD - FM maximal fluorescence in the presence of NRD - NRD nonradiative energy dissipation - PET photosynthetic electron transport rate - PFD photon flux density - PSII photon yield of PSII photochemistry at the actual reduction state in the light or dark - QA the primary electron acceptor of PSII - [ATP+ADP+AMP] - SVN Stern-Volmer nonphotochemical quenching - V violaxanthin - Z zeaxanthin We thank Connie Shih for skillful assistance in growing plants and for conducting HPLC analyses. A Carnegie Institution Fellowship to A.G. is also gratefully acknowledged.  相似文献   

20.
The photosynthetic apparatus in plants is protected against oxidative damage by processes that dissipate excess absorbed light energy as heat within the light-harvesting complexes. This dissipation of excitation energy is measured as nonphotochemical quenching of chlorophyll fluorescence. Nonphotochemical quenching depends primarily on the [delta]pH that is generated by photosynthetic electron transport, and it is also correlated with the amounts of zeaxanthin and antheraxanthin that are formed from violaxanthin by the operation of the xanthophyll cycle. To perform a genetic dissection of nonphotochemical quenching, we have isolated npq mutants of Chlamydomonas by using a digital video-imaging system. In excessive light, the npq1 mutant is unable to convert violaxanthin to antheraxanthin and zeaxanthin; this reaction is catalyzed by violaxanthin de-epoxidase. The npq2 mutant appears to be defective in zeaxanthin epoxidase activity, because it accumulates zeaxanthin and completely lacks antheraxanthin and violaxanthin under all light conditions. Characterization of these mutants demonstrates that a component of nonphotochemical quenching that develops in vivo in Chlamydomonas depends on the accumulation of zeaxanthin and antheraxanthin via the xanthophyll cycle. However, observation of substantial, rapid, [delta]pH-dependent nonphotochemical quenching in the npq1 mutant demonstrates that the formation of zeaxanthin and antheraxanthin via violaxanthin de-epoxidase activity is not required for all [delta]pH-dependent nonphotochemical quenching in this alga. Furthermore, the xanthophyll cycle is not required for survival of Chlamydomonas in excessive light.  相似文献   

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