Effects of Exogenously Applied Benzylaminopurine and Kinetin on the Ripening of Banana (Musa acuminata Colla var. William) Fruits

摘要

Although, the ripening of climacteric fruits such as bananas is known to be mainly triggered by ethylene, cytokinins may also intervene in the control and regulation of this process. Bananas were treated by dipping for 24 h in solutions of cytokininsat concentrations ranging from 10~(-6)to 10~(-3) M to determine effects of these phytohormones on some parameters during the fruit ripening. At all concentrations used, benzylaminopurine induced significant retentions of water in the peel of banana fruits. Only 10~(-3) M kinetin solution was significantly effective in inhibiting the decrease of water content in the peel. There was an inhibition of the accumulation of water in the pulp of bananas after treatments with kinetin or benzylaminopurine. Qualitative analysis of pigments in peel extracts revealed an inhibition of chlorophyll degradation after application of cytokinins. Thus, banana fruits treated with 10~(-3) M kinetin still contained only chlorophyll a whereas, fruits treated with 10~(-3) M benzylaminopurine contained both chlorophyll a and chlorophyll b at ripening stage 7. At this ripening stage, no chlorophyll could be detected in extracts from the peel of control fruits. There were increased accumulations of monoacylglycerol, triacylglycerol and free fatty acids in the peel of banana fruits treated with 10~(-3) M benzylaminopurine. Contrarily to apolar lipids, no remarkable effects of treatments of bananas with 10~(-3) M benzylaminopurine on polar lipids could be observed. These resultsindicated that cytokinins modulated the metabolism of photosynthetic pigments and lipids and changes in the water content and that chlorophyll b was converted into chlorophyll a before its degradation in the peel of banana fruits during the ripening process.