Ethylene formation in plant mitochondria. Dependence on the transport of 1‐aminocyclopropane‐1‐carboxylic acid across the membrane

Abstract

The mitochondrial fraction isolated from plumular hooks of etiolated pea seedlings (Pisum sativum L. cv. Kelvedon Wonder) displayed a ten‐fold higher rate of ethylene formation from 1‐aminocyclopropane‐1‐carboxylic acid [ACC; 3.2 nmol C2H4 (mg protein −1)h−1], than the tissue from which it was isolated. When the ionophores valinomycin or nigericin were added, a 60‐ to 70‐fold increase in activity in intact mitochondria over the activity in plumular hooks was obtained for ethylene formation under the same conditions, and a 20‐fold increase was obtained upon addition of gramicidin. The addition of ionophores did not affect the rate of ethylene formation in submitochondrial particles (55% inside‐out as determined by cytochrome oxidase latency) which already exhibited a 2–3‐fold higher specific activity than intact mitochondria. Low concentrations of the detergents cholate and deoxycholate increased mitochondrial ethylene formation activity and had no effect on the rate of the reaction in submitochondrial particles. These results support the suggestion that ACC conversion to ethylene is associated with the inner side of the inner mitochondrial membrane and that transport across the intact mitochondrial membrane is rate‐limiting in the reaction.