Ethylene, β-Cyanoalanine Synthase and Cyanide Insensitive Respiration in Ripening Apples: The Effect of Calcium

Abstract

In a climacteric fruit where increasing amounts of ethylene are produced during ripening, cyanide is stoichianetricly produced and methanisms must exist to allow cellular functions, such as respiration, to proceed in the presence of cyanide, as well as mechanisms to metabolize the cyanide. Apple fruit at different stages of ripeness were examined for ethylene production, β -cyanoalanne synthase activity, and cyanide insensitive repiration. The fruits were also treated with calcium to see how these membrane based processes were affected. Ethylene production in apple discs was inhibited by calcium after 4 hours, but the loss of ethylene production ability due to membrane senescence was partially prevented by calcium, and ethylene production after 24 hours was higher in the presence of calcium than in control tissue. In intact fruit ethylene evolution throughout the climacteric was unaffected by calcium. The increase in ethylene production was accompanied by increased β -cyanolalanine synthase activity, and calcium enhanced the activity at all stages of ripening. The fruits exhibited cyanide insensitive respiration at all stages of ripening, however, the fraction of the pathway operating in the absence of cyanide (the ρ value) was low, 0.05–0.15. The addition of calcium increased the ρ value fivefold in preclimacteric fruit and threefold in midclimacteric fruit even though the total respiration was reduced by calcium.