Physiology of banana ripening : a study of the effects of ethylene and kinetin, of cell permeability, and of changes in RNA and protein content

Ripening is a characteristic feature in the life of fleshy fruits. Unlike other plant growth phenomena such as flowering and seed germination, the initiation of ripening has not been linked to specific environmental factors such as length or water potential. However, ripening in fruits such as the banana is induced by detach­ment of the fruit from the plant, suggesting that an inhibitor of ripening is translocated into the attached fruit. Ripening may commence when the concentration of the inhibitor in the harvested fruit declines to a level such that tissue becomes susceptible to the endogenous ethylene of the preclimacteric fruit. The ensuing development of ripening involves an increase in enzyme activities, which may be due to activation of preexisting enzymes,. or de nova synthesis of enzymes. 0,anges in membrane permeability, which increase the access of substrates to enzymes, is one method of enzyme activation for which some evidence exists. This treatise examines the evidence pertaining to these theories of the induction and development of ripening, with respect to the banana. The possibility that cytokinins might serve partially or wholly as a ripening inhibitor was examined, by infiltrating transverse slices of banana with kinetin solutions. The role of endogenous ethylene in preclimacteric bananas was investigated by applying trace quantities of ethylene to the fruit. The correlation between permeability of pulp tissue and other ripening changes was determined. The RNA and protein contents of ripening fruit were examined in a search for evidence of de novo enzyme synthesis