Photochemical Activity of Chloroplasts from Wheat Grown Under Nitrogen Deficiency

T. E. Krendeleva,¹ V. V. Makarova,^1,2 G. P. Kukarskikh,¹ N. V. Nizovskaya,¹ and O. G. Lavrukhina¹

¹Department of Biophysics, School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (7-095) 939-11-15.

²To whom correspondence should be addressed.

Submitted June 18, 1996; revision submitted July 24, 1996.

Photosynthetic activity of 17-day-old seedlings grown on nitrogen deficient media and photochemical activity of chloroplasts isolated from the second leaf were studied. Nitrogen content per mg leaf dry and wet masses were 2-3 times lower than the control, but the chlorophyll contents were similar. Real and potential photosynthetic activities decreased per leaf and per dm² of the leaf area but were the same as control per mg of chlorophyll. Thylakoids isolated from the seedlings grown without nitrogen were not different from the control in protein content, rate of 2,6-dichlorophenolindophenol reduction, number of photosystem 2 reaction centers, or efficiency of excitation energy utilization. Assays of the rates of uncoupled electron transport, noncyclic phosphorylation, electron transport in the presence of ADP + P_i or uncoupler, and activity of Mg²⁺-dependent H⁺-ATPase indicated that, first of all, nitrogen deficiency damaged linear electron flow and phosphorylation coupling. But the rate of cyclic phosphorylation in the chloroplasts was higher than control. Thus, ATP deficiency for CO₂ fixation was compensated and photosynthetic function was stabilized at the beginning of nitrogen starvation of the plants.

KEY WORDS: nitrogen deficiency, wheat, Triticum aestivum L., CO₂ fixation, fluorescence, photosystems, photophosphorylation, chlorophyll, electron transport.

---