Water-stress-induced thermotolerance of photosynthesis in bean (Phaseolus vulgaris L.) plants: The possible involvement of lipid composition and xanthophyll cycle pigments
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A common feature in plants that are exposed to gradual stressful environmental factors is the development of a level of resistance to such constraints, which sometimes protects against different stressful environmental conditions. The aim of this study was to assess a possible cross-resistance between water stress and high-temperature stress and to gain a better knowledge regarding the physiological basis for heat resistance. The study was performed in two bean varieties; Orfeo INIA (OI) and Arroz Tuscola (AT) are a stress-resistant and stress-sensitive variety, respectively. An increased heat resistance in OI but not in AT results from water stress as revealed by the oxygen-evolution rate at 38 ◦C and the thermal threshold for non-reversible damage that was assessed by the temperature-dependent increases in basal fluorescence (F0); higher values of both parameters were observed in the leaves of waterstressed plants when compared to the control OI plants. The heat-shock proteins HSP70, HSP60 and HSP24 do not seem to be involved in the water-stress-induced resistance to high temperature because no difference in their contents was found between the water-stressed and control plants. The important features in the water-stressed OI plants, which can resist higher temperatures, are the maintenance of the xanthophyll pigment contents compared to the control plants and in contrast to the sensitive AT plants, an increase in phosphatidylglycerol and a reduction in the unsaturation level of the thylakoid fatty acids. The results from the comparative analyses of the xanthophyll, lipid and fatty acid compositions in the chloroplasts of well-watered and water-stressed AT and OI plants are discussed in terms of their possible involvement in conferring resistance to high temperature in water-stressed bean leaves.