NITRIC-OXIDE INHIBITS THE CYTOCHROME-OXIDASE BUT NOT THE ALTERNATIVE OXIDASE OF PLANT-MITOCHONDRIA

Oxygen consumption via the cytochrome pathway in isolated soybean (Gly cine max [L.] Merr,) cotyledon mitochondria was inhibited by nitric ox ide (NO) while respiration via the cyanide-insensitive alternative oxi dase was not significantly affected, Inhibition of cytochrome pathway activity was rapidly reversible upon depletion of the added NO. NO pro duction was also detected in solutions of NaNO2 plus ascorbate and the extent of cytochrome pathway inhibition was dependent on the NO2- con centration, Little inhibition of alternative pathway respiration was o bserved under similar conditions, The alternative oxidase may play a r ole in nitric oxide tolerance in higher plants and in organisms such a s trypanosomes which contain a plant-like alternative oxidase.