The Climacteric Rise in Fruit Respiration as Controlled by Phosphorylative Coupling

Abstract

This work concerns the climacteric rise in respiration of ripening fruit. The characteristics of the respiration of preclimacteric fruit have been contrasted with those of climacteric fruit. The respiration of the avocado fruit appears to be mediated by an organized respiratory complex. The active respiratory particles have been isolated from both preclimacteric and climacteric fruit. The oxidation of substrate by the respiratory particles of avocado is coupled to the oxidative production of ATP. Rate of substrate oxidation by the respiratory particles is dependent upon the concn. of exogenous phosphate acceptor, adenylate. Although rate of substrate oxidation is normally limited by the capacity of the phosphate accepting system, this limitation can be removed be agents such as DNP which sever the coupling of oxidation to phosphorylation. With the aid of the uncoupling agent, DNP, it has been shown that the rate of respiration of the preclimacteric, but not of the climacteric fruit is limited by the capacity of the phosphate transfer system. The fact that ripening avocado fruits contain a substance which, like DNP, acts as an uncoupling agent suggests that both the climacteric rise in respiration and the chemical changes of fruit ripening may be due to uncoupling: a decrease in synthesis or availability of ATP within the fruit.