The effect of growth at low temperature on photosynthetic characteristics and mechanisms of photoprotection of maize leaves

We examined the photosynthetic properties, the activity of antioxidantenzymes and the amount of caroten-oids of two maize genotypescharacterized by different sensitivity to low temperature. Plantsof the low-temperature-sensitive genotype A-619 and of the low-temperature-resistantgenotype VA-36 were grown at 25/20C (control plants) and at16/14C (plants grown at low temperature). Twenty-five daysafter seeding, the exposure to low temperature caused, in allplants, a reduction of leaf chlorophyll and carotenoid content,but an increase in the activity of the oxygen-detoxifying enzymes,superoxide dismutase and ascorbate per-oxidase. However, theresponse of photosynthesis, stomatal conductance and the fluorescenceproperties to light and temperature were not affected by growthat low temperature. Fifty days after seeding, photosynthesis, stomatal conductance,and fluorescence properties of A-619 leaves grown at low temperaturewere significantly reduced with respect to control plants atall temperatures and light intensities. In the leaves of A-619plants grown at low temperature, the electron transport ratewas not tightly down-regulated by carbon metabolism and an excessof electrons was shown by the increased ratio between the quantumyield of electron transport of photosystem II and the quantumyield of CO2 assimilation. On the contrary, VA-36 leaves grownat 16C maintained the same photosynthetic characteristics andphotochemical properties as control plants. The chlorophyllcontent of both genotypes and carotenoid content of A-619 plantswere lower in leaves of plants maintained at 16C than in thosegrown at 25C. In contrast, the carotenoid content of VA-36leaves of plants grown at low temperature were higher than inplants grown at 25C. The activity of superoxide dismutase and ascorbate peroxidaseof VA-36 plants grown at low temperature were higher than incontrols. In A-619 plants grown at fow temperature the activityof superoxide dismutase was higher than in controls, but theactivity of ascorbate peroxidase was lower than in controls.Our findings suggest that when maize plants are grown at lowtemperature the electron transport rate may be in excess ofcarbon metabolism and electrons may be used to reduce oxygen.A co-ordinate increase of pigment amounts and of the activityof oxygen-detoxifying enzymes is necessary to protect maizeleaves from the accumulation of oxygen radicals at low temperature.In A-619 plants, the carotenoid content did not increase andthe activity of ascorbate peroxidase was low when plants wereexposed to low temperature for 50 d. As a result, the photochemicalapparatus of A-619 leaves was damaged and photo-oxidation occurred.These experiments also indicated that when photosynthesis wasreduced by a transitory reduction of temperature, the electrontransport was still tightly down-regulated by carbon metabolismand the photosynthetic apparatus of both genotypes was not damaged. Key words: Photosynthesis, electron transport, antioxid-ants, carotenoids, low temperature.     

Cyclic electron flow plays an important role in photoprotection of tropical trees illuminated at temporal chilling temperature

Our previous study indicated that PSII is more sensitive to chilling and light stress than PSI in tropical trees, and Erythrophleum guineense is more sensitive to chilling stress than Dalbergia odorifera and Khaya ivorensis, but the underlying physiological mechanisms are unclear. Although recent studies have reported that cyclic electron flow (CEF) plays an important role in photoprotection, the role of CEF in protecting PSI and PSII of tropical tree species remains unclear. We investigated the effect of temporal chilling temperature on energy distribution in PSII, the redox state of P700 and CEF in the above-mentioned tropical evergreen tree species grown in an open field. Our results indicated that the overclosure of PSII reaction centers at chilling temperature led to excess excitation pressure in PSII. At the temporal chilling temperature under low light, PSI acceptor side limitation [Y(NA)] was lower than those at 25°C for all species. Although the effective quantum yield of CEF [Y(CEF)] was not significantly stimulated in E. guineense and K. ivorensis under temporal chilling at low light levels, the ratio of Y(CEF) to the effective quantum yield of PSII [Y(II)] significantly increased. Under chilling conditions Y(CEF)/Y(II) was stimulated much more in K. ivorensis and D. odorifera compared with that in the chilling-sensitive E. guineense. These results suggested that stimulation of Y(CEF)/Y(II) plays an important role in protecting PSI and PSII from photoinhibition caused by chilling stress.     

Anthocyanin accumulation in the illuminated surface of maize leaves enhances protection from photo-inhibitory risks at low temperature, without further limitation to photosynthesis

At suboptimal temperatures, anthocyanins accumulate in the illuminated leaf surface of some maize genotypes and, if the anthocyanins shade chloroplasts, they can effectively reduce the risk of photo‐inhibition but also photo‐synthesis. To investigate this phenomenon, gas exchange, fluorescence, superoxide dismutase activity and xantho‐phyll composition of anthocyanin‐containing HOPI and anthocyanin‐deficient W22 maize genotypes were measured in either white or red light, where the latter is not absorbed by anthocyanins. Despite differences in light absorption in chloroplasts, photosynthesis did not differ between HOPI and W22 under either light source, suggesting that neither CO₂ supply nor photochemistry were more limiting in red leaves than in green leaves. In fact, no major differences in transpiration were detected. The ΔF/F_m (photosystem II quantum yield) of HOPI in white light was higher than in red light and higher than ΔF/F_m of W22 with either light source. This probably compensated for the lower white light absorption of HOPI chloroplasts compared with W22 because of the presence of anthocyanins and led to similar rates of calculated electron transport for both genotypes. After exposure to high white light at 5 °C, xanthophyll de‐epoxidation and superoxide dismutase activity were lower in HOPI than in W22. Further, HOPI could be exposed to a much higher irradiance than W22 before F_v/F_m was reduced to that of W22.     

Respiratory acclimation in Arabidopsis thaliana leaves at low temperature

Acclimation of 25 degrees C-grown Arabidopsis thaliana at 5 degrees C resulted in a marked increase of leaf respiration in darkness (Rd) measured at 5 degrees C. Rd was particularly high in leaves developed at 5 degrees C. Leaf respiration (non-photorespiratory intracellular decarboxylation) in the light (Rl) also increased during cold acclimation, but less so than did Rd. The ratio Rd/Pt (Pt - true photosynthesis) was higher in more acclimated or cold-developed leaves, while the ratio Rl/Pt remained unchanged. In cold-acclimated leaves, Rl did not correlate with 3-phosphoglycerate and pyruvate nor with hexose phosphate pools in the cytosol. Rl in A. thaliana leaves was probably not limited by the substrate during cold acclimation. Under the conditions tested, Rd was more sensitive to low temperature stress than Rl.     

Quenching of the fluorescence emitted by P695-682 at room temperature in etiolated illuminated leaves

Chlorophyll(ide) fluorescence emission decreases at room temperature during completion of protochlorophyll(ide) reduction. The process responsible for this quenching is parallel to the P_688-676 P_695-682 transition. It proceeds equally well in darkness and in the light. It consists in a decrease of the fluorescence yield of chlorophyll(ide) in P_695-682. Apparently, room temperature P_695-682 fluorescence is regulated by a conjunction of factors such as energy transfers and photobiochemical activities.Abbreviations NADP nicotinamide-adenine dinucleotide phosphate - CPI chlorophyll-protein-complex I - CPII chlorophyll-protein-complex II Aspirant du Fond National de la Recherche Scientifique, Belgium     

Cerebrosides in grapevine leaves: distinct composition of sphingoid bases among the grapevine species having different tolerances to freezing temperature

Cerebrosides from leaves of three grapevine species were analyzed in detail. The relative proportions of 8-E/Z isomers of 4-hydroxy-8-sphingenines [i.e. 8-E/Z t18:1(8E) and (8Z)] differed amongst the species in respect to freezing tolerance. This suggests that the occurrence of high levels of t18:1(8Z) in cerebrosides is correlated with freezing tolerance in these species.     

Response of the photosynthetic apparatus in maize leaves grown at low temperature on transfer to normal growth temperature

Low temperatures are known to restrict chloroplast development and prevent the attainment of photosynthetic competence in maize leaves. The responses of the photosynthetic apparatus of mature maize leaves grown at 14°C on transfer of the plants to 25°C are examined. The synthesis of thylakoid proteins increased immediately on transfer of leaves from 14 to 25°C, with a dramatic accumulation of thylakoid proteins and chlorophylls occurring after 3 d at 25°C. Thylakoid structure and organization also became similar to those observed in leaves grown at 25°C over this period. However, no comparable development of photosynthetic competence in photosystems I and II or in the rate of CO₂ assimilation was observed on transfer of leaves from 14 to 25°C. Immunocytological analyses demonstrated heterogeneity in the distribution of a range of thylakoid proteins (cy tochrome f, the α and β subunits of the coupling factor, Dl of the photosytem II reaction centre, the 33kDa protein of the extrinsic oxygen-evolving complex of photosystem II, and subunit II of photosystem I between mesophyll cells in leaves grown at 14°C, and in the responses of individual proteins to transfer of the leaves to 25°C. Such heterogeneity between mcsophyll cells would account for the inability of the leaves to develop the expected degree of photosynthetic competence on transfer to 25°C. The effects of low growth temperatures on chloroplast biogenesis are complex, as are the changes induced by the transfer ofleaves grown at low temperatures to optimal growth temperature, and both these factors may limit the canopy development and photosynthetic productivity of crops in temperate regions.     

Pigment-protein complexes of illuminated etiolated leaves

Photoconversion of protochlorophyllide in etiolated leaves of Avena sativa L., var. Pennal or Peniarth and Phaseolus vulgare L., var. `The Prince' results in the sequential appearance of spectrally distinct chlorophyllide complexes (Chlide 678, 684, and 672). This paper reports on the generation of similar forms in vitro, under controlled conditions, using well characterized etioplast membranes enriched in the enzyme protochlorophyllide reductase. Excess NADP<sup>+</sup> and NADPH stabilize complexes related to Chlide 678 and Chlide 684, respectively, whereas addition of exogenous Pchlide induces formation of a species related to Chlide 672. Evidence is provided to support the suggestion that Chlide 678 and Chlide 684 represent ternary complexes of the enzyme protochlorophyllide reductase, with Chlide and either NADP<sup>+</sup> (Chlide 678) or NADPH (Chlide 684). Chlide 672 is seen as `free' pigment dissociated from the enzyme. The role of Pchlide in this dissociation, observed spectroscopically as the `Shibata shift,' is discussed.     

Photoinactivation of catalase at low temperature and its relevance to photosynthetic and peroxide metabolism in leaves

Abstract In green as well as in etiolated leaves of rye (Secale cereale L. ev. ‘Halo’), exposed to strong light at low temperature (0.4°C) catalase was inactivated. Other heme-containing enzymes (peroxidases) and various enzymes of photosynthetic, photorespiratory or peroxide metabolism were not photoinactivated. After returning plants from a low to a physiological temperature (22°C), catalase activity recovered within 12 h through new synthesis. The leaf contents of H₂O₂ and organic peroxides were not affected by the photoinactivation of catalse. The content of malondialdehyde generally increased after exposure to a higher light intensity. High-light-induced increases of ascorbate, and particularly of glutathione, were more marked in catalase-deficient than in normal leaves. Photoinactivation of catalase was accompanied by severe inhibition of photosynthesis. Photoinhibition of photosynthesis was not related to the lack of catalase because photosynthesis was not impaired when catalase activity was kept low by growing the plants under non-photorespiratory conditions. Photoinhibition appeared to result from photodamage in primary photochemistry of photosystem II, as indicated by a decrease of the maximal variable fluorescence. Photoinhibition of photosynthesis and of catalase have in common that in both instances proteins are involved that are continuously inactivated in light and, therefore, particularly sensitive to stress conditions that prevent their replacement by repair synthesis.     

In vivo respiratory metabolism of illuminated leaves

Day respiration of illuminated C(3) leaves is not well understood and particularly, the metabolic origin of the day respiratory CO(2) production is poorly known. This issue was addressed in leaves of French bean (Phaseolus vulgaris) using (12)C/(13)C stable isotope techniques on illuminated leaves fed with (13)C-enriched glucose or pyruvate. The (13)CO(2) production in light was measured using the deviation of the photosynthetic carbon isotope discrimination induced by the decarboxylation of the (13)C-enriched compounds. Using different positional (13)C-enrichments, it is shown that the Krebs cycle is reduced by 95% in the light and that the pyruvate dehydrogenase reaction is much less reduced, by 27% or less. Glucose molecules are scarcely metabolized to liberate CO(2) in the light, simply suggesting that they can rarely enter glycolysis. Nuclear magnetic resonance analysis confirmed this view; when leaves are fed with (13)C-glucose, leaf sucrose and glucose represent nearly 90% of the leaf (13)C content, demonstrating that glucose is mainly directed to sucrose synthesis. Taken together, these data indicate that several metabolic down-regulations (glycolysis, Krebs cycle) accompany the light/dark transition and emphasize the decrease of the Krebs cycle decarboxylations as a metabolic basis of the light-dependent inhibition of mitochondrial respiration.     

低温弱光下类囊体腔内质子由CF_0渗漏引起黄瓜类囊体耦联度降低

毫秒延迟发光测定结果表明低温弱光处理黄瓜叶片导致类囊体原位 (in situ)耦联度显著降低。DCCD可以恢复低温弱光处理的黄瓜叶片的毫秒延迟发光的慢相强度和反映类囊体膜质子吸收的 9- AA(9- Aminoacridine)荧光猝灭能力 ,说明类囊体耦联度降低的原因是质子由 CF0 大量快速渗漏。进一步研究结果表明 ,活性氧和 CF1的脱落不是低温弱光引起黄瓜类囊体耦联度降低的根本原因。     

Chloroplast movement provides photoprotection to plants by redistributing PSII damage within leaves

Plants use light to fix carbon through the process of photosynthesis but light also causes photoinhibition, by damaging photosystem II (PSII). Plants can usually adjust their rate of PSII repair to equal the rate of damage, but under stress conditions or supersaturating light-intensities damage may exceed the rate of repair. Light-induced chloroplast movements are one of the many mechanisms plants have evolved to minimize photoinhibition. We found that chloroplast movements achieve a measure of photoprotection to PSII by altering the distribution of photoinhibition through depth in leaves. When chloroplasts are in the low-light accumulation arrangement a greater proportion of PSII damage occurs near the illuminated surface than for leaves where the chloroplasts are in the high-light avoidance arrangement. According to our findings chloroplast movements can increase the overall efficiency of leaf photosynthesis in at least two ways. The movements alter light profiles within leaves to maximize photosynthetic output and at the same time redistribute PSII damage throughout the leaf to reduce the amount of inhibition received by individual chloroplasts and prevent a decrease in photosynthetic potential.     

Changes in fluorescence quenching brought about by feeding dithiothreitol to illuminated leaves

When CO₂ is abruptly removed from the atmosphere surrounding an illuminated leaf, the primary electron-accepting plastoquinone of photosystem II (Q_A) (as measured by photochemical quenching, q_p) is rapidly reduced and then, after some seconds, becomes more oxidized. The reoxidation of Q_A⁻ is accompanied by an increase in ΔpH (as measured by nonphotochemical quenching, q_N) with kinetics consistent with a causal relationship. The fact that, in such circumstances, Q_A can become more oxidized in the absence of CO₂ than in its presence indicates a diminished rate of reduction of Q_A, consequent upon impaired photosystem II efficacy. Dithiothreitol (DTT) feeding, which does not affect quantum yield or the maximum rate of photosynthesis, inhibits the reoxidation of Q_A⁻ but not the increase in the proton gradient. When leaves are reilluminated in high light following a dark interval of several minutes, DTT also abolishes the separation in time between the first maximum in q_P and the first maximum in the rate of O₂ evolution. It also diminishes subsequent oscillations. These results are held to demonstrate ΔpH control of photosystem II and are consistent with DTT inhibition of the xanthophyll cycle and hydrogen peroxide reduction. They support the concept that oxygen and hydrogen peroxide are involved, as Hill oxidants, in a pH-related manner, during oscillatory behavior.     

Candidate loci for phenology and fruitfulness contributing to the phenotypic variability observed in grapevine

Key message

In this study, we identified several genes, which potentially contribute to phenological variation in the grapevine. This may help to maintain consistent yield and suitability of particular varieties in future climatic conditions.

Abstract

The timing of major developmental events in fruit crops differs with cultivar, weather conditions and ecological site. This plasticity results also in diverse levels of fruitfulness. Identifying the genetic factors responsible for phenology and fertility variation may help to improve these traits to better match future climates. Two Vitis vinifera populations, an F1 progeny of Syrah × Pinot Noir and a phenological core collection composed of 163 cultivars, were evaluated for phenology and fertility subtraits during three to six growing seasons in the same geographical location. The phenotypic variability in the core collection mostly overlapped with that observed in the F1 progeny and several accessions had exceeding values of phenological response. The progeny population was used together with SSR and SNP markers to map quantitative trait loci (QTLs). This allowed us to detect nine QTLs related to budburst, flowering beginning, the onset of ripening (véraison) and total fertility, explaining from 8 to 44 % of phenotypic variation. A genomic region on chromosome 15 was associated with budburst and véraison and two QTLs for fruitfulness were located on chromosomes 3 and 18. Several genes potentially affecting fertility and the timing of fruit development were proposed, based on their position and putative function. Allelic variation at these candidate loci may be explored by sampling accessions from the core collection.     

Photoinhibition and photoprotection in senescent leaves of field-grown wheat plants

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.     

Developmental history affects the susceptibility of spinach leaves to in vivo low temperature photoinhibition

Room temperature chlorophyll a fluorescence was used to determine the effects of developmental history, developmental stage, and leaf age on susceptibility of spinach to in vivo low temperature (5°C) induced photoinhibition. Spinach (Spinacia oleracea cv Savoy) leaves expanded at cold hardening temperatures (5°C day/night), an irradiance of 250 micromoles per square meter per second of photosynthetic proton flux density, and a photoperiod of 16 hours were less sensitive than leaves expanded at nonhardening temperatures (16 or 25°C day/night) and the same irradiance and photoperiod. This differential sensitivity to low-temperature photoinhibition was observed at high (1200) but not lower (500 or 800 micromoles per square meter per second) irradiance treatment. In spite of a differential sensitivity to photoinhibition, both cold-hardened and nonhardened spinach exhibited similar recovery kinetics at either 20 or 5°C. Shifting plants grown at 16°C (day/night) to 5°C (day/night) for 12 days after full leaf expansion did not alter the sensitivity to photoinhibition at 5°C. Conversely, shifting plants grown at 5°C (day/night) to 16°C (day/night) for 12 days produced a sensitivity to photoinhibition at 5°C similar to control plants grown at 16°C. Thus, any resistance to low-temperature photoinhibition acquired during growth at 5°C was lost in 12 days at 16°C. We conclude that leaf developmental history, developmental stage, and leaf age contribute significantly to the in vivo photoinhibitory response of spinach. Thus, these characteristics must be defined clearly in studies of plant susceptibility to photoinhibition.