Protective effect of exogenous nitrate on the mitochondrial ultrastructureof Oryza sativa coleoptiles under strict anoxia

The effect of exogenous KNO3, the terminal acceptor of electrons in oxygen- free medium, on mitochondrial ultrastructure and on the growth rate of 4-da y-old rice coleoptiles under strictly anoxic conditions was studied. Exogen ous nitrate (10 mM) did not exert any significant effect on the growth rate of coleoptiles of intact seedlings compared to their growth in KNO3-free m edium. Anaerobic incubation of detached coleoptiles in KNO3-free medium for 48 h resulted in the complete destruction of mitochondrial and other cell membranes. In the presence of KNO3, no mitochondrial-membrane destruction w as observed even after 48 h anoxia although the mitochondrial ultrastructur e was modifed. Cristae were arranged in parallel rows and elongated dumbbel l-shaped mitochondria appeared in some cells. The data obtained indicate a protective role of exogenous nitrate as electron accepters in oxygen-free m edium. The results of the present investigation are discussed and compared with reports of either markedly damaging or favorable effects of exogenous nitrate on the growth, metabolism, and energetics of rice and other plants under hypoxic and anoxic conditions.