FLESHY fruits have been divided int

FLESHY fruits have been divided into two classes on the basis of their respiratory behaviour during ripening: climacteric fruit, such as bananas, which undergo a large increase in respiration (climacteric rise) accompanied by marked changes in composition and texture, and non-climacteric fruit such as citrus, which show no changes in respiration that can be associated with distinct changes in the composition of the fruit1. An increase in the level of endogenous ethylene is considered to be the immediate trigger of ripening in climacteric fruits2. Fruits of this class usually produce large amounts of ethylene once ripening is under way. They may also be induced to ripen by treatment with ethylene at concentrations above about 0.1 p.p.m. for a suitable period3. The ripening induced by exogenous ethylene has been considered to be qualitatively identical with that which occurs naturally3. In both cases, once ripening is induced it has been considered that endogenous ethylene production rises autocatalytically4. Uninjured citrus fruit have been shown to produce low amounts of ethylene5. Their respiration may be increased by treatment with ethylene6 and disappearance of chlorophyll (colouring) and ageing may be more rapid18.