Esterification of Phosphate in Ripening Fruit.

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Abstract
Oxygen consump-tion markedly increases during the ripening of many fruits resulting in a "climacteric maximum" of respiration, followed by a post-climacteric respiratory decline. Robertson and Turner (Australian Jour. Sci. Research Series B4: 75, 1951) proposed that the occurrence of limited respiration during the preclimacteric period of fruit development may be due to the limited availability of phosphate acceptors. Oxidative phosphorylation in intact tomato fruit was investigated by P32 tracer techniques and shown to be operative during early (preclimacteric) ripening and likewise, during the postclimacteric period of senescence. The percentage of P32 incorporated into organic esters by oxidative phosphorylation reached a maximum in early, preclimacteric fruit, and did not decrease until after the onset of pink color. It was possible to prevent phosphorylation by the uncoupling action of dinitrophenol and also by bruising injury, but complete disappearance of phosphorylating capacity did not occur naturally until the termination of senescence. Green mature fruit failed to ripen normally when treated with dinitrophenol, or after bruising. The role of oxidative phosphorylation in fruit ripening would thus point toward the existence of energy requiring syntheses, which are essential to the completion of ripening by senescing fruit. That climacteric is induced by increased availability of ADP would similarly be consistent with the concept of fruit ripening as a process initiated by synthesizing activities.

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