Regulation of nitrate reduction in wheat leaves.

Wheat leaves exposed to 710 nm monochromatic light, when only photosystem 1 operates, reduced small but significant amount of nitrate to nitrite. This could be due to partial inhibition of mitochondrial oxidation of NADH, brought about by cyclic photophosphorylation. Under dark aerobic conditions, citric acid cycle intermediates only slightly stimulated nitrate reduction. Under dark anaerobic conditions, when maximum reduction of nitrate occurred, the time course showed a 1:1 stoichiometry between nitrite and CO2. It is suggested that for maximum reduction of nitrate under physiological conditions, CO2 fixation and export of ATP via triose phosphate shuttle is essential.