Ferredoxin-Dependent Photosynthetic Electron Transport and Coupled Processes of Energy Storage in Chloroplasts of Wheat Plants Grown under Different Levels of Nitrogen Supply

The rates of electron transfer in the presence of natural cofactors, ferredoxin and NADP, which were added in the amounts catalyzing noncyclic or cyclic electron transfer, were studied in thylakoids isolated from 17-day-old wheat seedlings. Upon excitation of both photosystems (PS) of photosynthesis, the potential rate of NADP reduction in thylakoids isolated from plants grown on nitrogen-free nutrient solution did not differ from that in thylakoids from the control plants. However, the P/2e ratio was significantly lower in thylakoids isolated from nitrogen-deficient plants. On the contrary, in the presence of DCMU, the rate of PSI-driven electron transfer from an artificial donor to NADP was considerably higher in these than in the control thylakoids. In the presence of ferredoxin under anaerobic conditions, the rate of phosphorylation coupled to cyclic electron transport was also significantly higher in thylakoids isolated from nitrogen-deficient plants, than in thylakoids isolated from control plants. Our data show that PSI-driven electron transport and cyclic photophosphorylation are activated in nitrogen-starved wheat plants, at least at the initial stages of starvation.