PHOTOCHEMICAL ACTIVITY OF CHLOROPLASTS FROM WHEAT GROWN UNDER NITROGEN DEFICIENCY

Photosynthetic activity of 17-day-old seedlings grown on nitrogen defi cient media and photochemical activity of chloroplasts isolated from t he second leaf were studied. Nitrogen content per mg leaf dry and wet masses were 2-3 times lower than the control, but the chlorophyll cont ents were similar. Real and potential photosynthetic activities decrea sed per leaf and per dm(2) of the leaf area but were the same as contr ol per mg of chlorophyll. Thylakoids isolated from the seedlings grown without nitrogen were not different from the control in protein conte nt, rate of 2,6-dichlorophenolindophenol reduction, number of photosys tem 2 reaction centers, or efficiency of excitation energy utilization . Assays of the rates of uncoupled electron transport, noncyclic phosp horylation, electron transport in the presence of ADP + P-i or uncoupl er, and activity of Mg2+-dependent H+-ATPase indicated that, first of all, nitrogen deficiency damaged linear electron flow and phosphorylat ion coupling. But the rate of cyclic phosphorylation in the chloroplas ts was' higher than control. Thus, ATP deficiency for CO2 fixation was compensated and photosynthetic function was stabilized at the beginni ng of nitrogen starvation of the plants.