Studies in the nitrogen metabolism of the apple fruit. Changes in the nitrogen metabolism of the apple during the normal and ethylene-induced climacteric rise in rate of respiration.

During work carried out over a number of years, it has been found repeatedly that, in Bramley's Seedling apples which have been gathered before the onset of the respiration climacteric and placed in storage, there is a slow rise in net protein content during the period when the respiration climacteric occurs (see, e.g., Hulme, 1936b). It is not certain, however, that there is a direct connexion between these two phenomena; it may be that both are changes normally occurring in ripening fruit and that their concurrence may be fortuitous. Kidd & West (1932) have demonstrated that the respiration climacteric can be induced even in immature fruits by treatment with ethylene. A net rise in protein content, therefore, in relatively immature apples during an ethylene-induced climacteric rise in respiration would be strong presumptive evidence that the two phenomena are intimately connected. The experiments described in this paper were designed, primarily, to ascertain whether this is the case. Data are also given for changes occurring during the 'normal' (i.e. not ethylene-induced) climactericriseinrespirationwhich occurseventually even in immature fruits. Data on the nitrogen metabolism of apples at various stages of development on and off the tree, which have accumulated in this laboratory over a number of years, have suggested that, of the soluble nitrogen fractions presumably involved in protein synthesis, asparagine nitrogen is most closely associated with rise or fall in protein. The present experiments provided an opportunity for studying such a relationship over a short specialized period in the ontogeny of the fruit. The period of the climacteric rise in respiration in immature fruits is especially suitable for such a study, since it embraces a relatively rapid rise in protein under conditions of constant content of total nitrogen.