ИСТИНА

Several lines of evidence suggest that water deficit induce the allocation of photosynthetic electrons to O2 particularly in wheat (Triticum aestivum L.). We have found that electron transport activity in the whole photosynthetic electron transport chain (PETC) slightly increased in drought-resistant wheat cultivar Saratovskaya 29, but decreased in drought non-resistant cultivar Opal under drought stress. However the electron transport activity of photosystem (PS) I and PS II were decreased in both cultivars. An increase in the whole electron transport rate when both photosystems decrease their activity may be caused by more effective reoxidation of plastoquinone (PQ) pool. The reoxidation of PQ-pool could be promoted particularly by O2 photoreduction. Indeed, it was found that oxygen photoreduction with Н2О2 generation increases significantly in drought-resistant wheat, but decreases in the sensitive cultivar under drought stress. On contrary, the PS I associated Mehler reaction that result in superoxide generation decreases in the resistant cultivar and stays constant in the sensitive one. Strikingly opposite effect of the drought stress on O2 photoreduction in two wheat cultivars may results from the different intramembrane changes occurring in thylakoids under water deficit.