Changes in the Activity and Expression of 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase, ACC Oxidase, and Phenylalanine Ammonia-lyase in Asparagus Spears in Response to Wound-induced Ethylene Synthesis
The molecular and enzymatic changes that follow harvesting of asparagus are important aspects for postharvest deterioration. To define the factors contributing to postharvest deterioration, the early changes in ethylene production and the activities and expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase, ACC oxidase, and phenylalanine ammonia-lyase (PAL) were studied in whole spears and in excised top and bottom portions. As a result of wounding, ethylene production was found higher in both top and bottom portions compared with whole spears but followed the same trend reaching the peak at 16 hours after harvest. ACC synthase was rapidly induced in excised top portions but no significant ACC synthase activity was observed in excised bottom portions. In top portions, ACC synthase reached a peak 8 hours after harvest and thereafter started to decline. In contrast to ACC synthase, ACC oxidase was induced markedly in both top and bottom portions and remained high until 16 hours after excision. On the other hand, PAL greatly increased in activity in bottom portions but not in excised tops. Northern blot analysis showed that increased mRNA levels coincided well with the excision-promoted increases in enzyme activity and ethylene production.