Nitrate-dependent o(2) evolution in intact leaves.

Evolution of O(2) by illuminated intact detached leaves from barley (Hordeum vulgare L. cv Athos) and pea (Pisum sativum L. cv Lincoln) in a CO(2)-saturating atmosphere was enhanced when KNO(3) (1-2.5 millimolar) had been previously supplied through the transpiration stream. The extra O(2) evolution observed after feeding KNO(3) increased with the light intensity, being maximal at near saturating photon flux densities and resulting in no changes in the initial slope of the O(2)versus light-intensity curve. No stimulation of O(2) evolution was otherwise observed after feeding KCl or NH(4)Cl. The data indicate that nitrate assimilation uses photosynthetically generated reductant and stimulates the rate of non-cyclic electron flow by acting as a second electron-accepting assimilatory process in addition to CO(2) fixation.