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.     

Functional organization of thylakoid membranes in viable pea mutants with low chlorophyll content

The functional organizations of thylakoid membranes from wild type pea ( Pisum sativum L. cv. Kapital) and two viable mutants with low chlorophyll (Chl) contents were compared. Nuclear mutations in mutants 7 and 42 led to two- and three-fold decrease in total chlorophyll content, respectively. In spite of low Chl content mutants showed 80% photosynthetic activity, biological productivity, and seed production. It has been shown that mutant membranes differed from that of wild type by Chl distribution between the pigment-protein complexes and by stoichiometry of the main electrontransport complexes. The ratio photosystem I (PSI): photosystem II (PSII): cytochrome (Cyt) bjf complex: Chl was 1:1.1:1.2:650 in wild type chloroplasts, 1:1.8:1.7:600 in mutant 7 , and 1:1.5:1.9:350 in mutant 42 . PSI- and PSII-dependent electron-transport activities were enhanced in the mutants per mg Chl in proportion to number of reaction centers. The activity of the non-cyclic electron-transport chain increased in proportion to PSII and Cyt bjf complexes. The amount of ATP synthetase per unit of Chl as estimated by H⁻ATPase activity was much greater in mutant thylakoids, which is favorable for photosynthetic energy transduction. The low content of the light-harvesting complexes (LHC) in mutants is compensated by an increase of the number of PSII and Cyt bjf complexes, which eliminates the bottleneck at the site of plastoquinone oxidation.