Abstract
The relationship between ethylene biosynthesis and cyanide metabolism was investigated in apple fruit during their development and during storage after harvest. The rate of ethylene production and the activity of β-cyanoalanine synthase, which catalyzes the reaction between cysteine and HCN to form β-cyanoalanine, were very low in young immature apple fruit but increased markedly with the onset of ripening. At the same time, corresponding increases in the ACC and cyanide content were also observed, although the changes in the cyanide content were not so large. The rapid parallel increase in β-cyanoalanine synthase activity with the increase in ACC content and rate of ethylene production clearly demonstrates that an active cyanide metabolism begins to operate with the onset of ripening of apple fruit. Since the development of cyanide-resistant respiration has so far been recognized in ripening fruits, the active cyanide metabolism by β-cyanoalanine synthase may be involved in the development of the alternative pathway. The localization of cyanide in the tissues of apple flesh was tentatively investigated. Some component(s) which react with bromine to yield BrCN were found in the precipitated fraction of the apple flesh homogenate indicating that the cyanide is closely associated with membrane structures. Its function and subcellular localization are, though, not clear at present.
