Moderately elevated temperature eliminates resistance of rice plants with enhanced expression of glutathione reductase to intensive photooxidative stress

We developed transgenic rice plants (Oryza sativa L. cv. Daeribbyeo) overproducing cytosolic glutathione reductase (GR) using a GR gene from Brassica campestris and studied their response to photo-oxidative stress in the presence of methyl viologen (MV, 10 and 50 muM concentrations) under room (25 C) and moderately elevated (35 C) temperature by analysis of chlorophyll (Chl) a fluorescence parameters (F-V/F-M, q(N), and q(P)) and of Chl content. Elevated temperature enhanced and accelerated the photo-oxidative damage to photosynthetic apparatus expressed mainly by a fast decrease of qN. Higher temperature supported the protective reaction in transformed rice plants for lower MV concentration (10 muM) and eliminated the enhanced tolerance of photosystem 2 photochemistry to photooxidative stress for higher (50 muM) MV concentration. Different mechanisms and temperature dependence of oxidative and protective reactions explain the results.