Effect of high temperature conditioning on ethylene, phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase activities in flavedo of chilled 'Fortune' mandarin fruit

The susceptibility of (Fortune, citrus fruit to chilling injury (CI) was markedly decreased by conditioning the fruit for 3 days at 37 degrees C. Rate of ethylene formation and changes in the activities of the phenolic enzymes, phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO), were measured in conditioned and non-conditioned mandarins during temperature storage. No correlation was found between the development of chilling symptoms in non-conditioned fruit and the changes in PPO and POD activities in the flavedo. The POD activity was higher in high temperature conditioned mandarins than in non-conditioned mandarins throughout the storage period. The increase in peel damage was concomitant with an increase in PAZ, activity, which followed that in ethylene production. These responses of 'Fortune' fruit to chilling were overriden by the heat treatment given before chilling exposure. Our data suggest that the reduction in CI induced by heat conditioning may involve changes in ethylene production, and PAL and POD activities.