High temperature effects on light sensitivity in the two high mountain plant species Soldanella alpina (L.) and Rannunculus glacialis (L.)

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anglais. The susceptibility to high temperature-induced photoinhibition was investigated in leaves of two high mountain plant species, S. alpina and R. glacialis. In both species, PSII was similarly photoinactivated at 38degreesC in the light. However, recovery from damage was much faster in S. alpina and depended on protein synthesis. In contrast, recovery was independent from protein synthesis in R. glacialis. Heat-induced photoinactivation in both species was accompanied by: (1) a decrease in relative photosynthetic electron transport rates, (2) an increase in non-photochemical chlorophyll fluorescence quenching, (3) a strong accumulation of zeaxanthin, (4) a marked decrease in soluble carbon metabolites and (5) an increase in lipid metabolism products, which was more pronounced in R. glacialis than in S. alpina. These results indicate that carbon assimilation was inhibited and that membranes were affected. Lipid peroxidation and possible membrane disintegration might limit the repair of damaged PSII in R. glacialis, while S. alpina appears to be protected by carotenoids and antioxidants. A marked decrease in alpha-tocopherol content and an increase in reduced ascorbate indicated lipid peroxide scavenging activity in S. alpina. When zeaxanthin synthesis was impaired by DTT, photoinhibition increased And (x-tocopherol accumulated in R. glacialis. The increased susceptibility of R. glacialis leaves to light-induced photoinhibition after growth at mode rate temperature (Streb et al., 2003a) and the inability to repair heat-induced damage might limit the distribution of R. glacialis to lower altitudes in the Alps.