SOFTENING OF SEVERAL FRUITS AND VEGETABLE S AT LOW HUMIDITY WITH RESPECT TO THEIR ENDOGENOUS ETHYLENE CONCENTRATIONS

Induction of softening in banana, cucumber, carrot and Japanese radish at low relative humidity (55% RH) was investigated with respect to th eir endogenous ethylene production. In banana, exogenous ethylene pret reatment rapidly hastened yellowing of the peel and softening of the f lesh at both high and low RH. However, pretreatment with diazocyclopen tadiene (DACP), an inhibitor of ethylene action, inhibited yellowing b ut did not prevent softening at high and low RH. In cucumber, carrot, and Japanese radish, softening of the firmness progressed at low RH ev en though endogenous ethylene activity was inhibited by DACP pretreatm ent. In cucumber, the flesh softened rapidly at low RH which was posit ively correlated to the increase in water soluble pectin and a decreas e in sodium hexametaphosphate soluble pectin. These results may indica te that induction of softening in several types of fruits and vegetabl es proceeds independent of endogenous ethylene concentration, and that the degradation of cell wall polysaccharides is induced directly by w ater deficit stress.