Wound-induced ethylene synthesis and expression and formation of 1-aminocyclopropane-1-carboxylate (ACC) synthase, ACC oxidase, phenylalanine ammonia-lyase, and peroxidase in wounded mesocarp tissue of Cucurbita maxima

1-Aminocyclopropane-1-carboxylate (ACC) synthase was rapidly induced in mes ocarp tissue of Cucurbita maxima after wounding in the cut surface layer in 1 mm thickness (ca, 9 cells) (first layer) in both the enzyme activity and the levels of transcript, This led to a rapid accumulation of ACC and henc e ethylene production, In the inside tissue (1-2 mm) (second layer), no sig nificant induction of ACC synthase was observed, which resulted in a low le vel of ACC, although ethylene was evolved at a much lower rate than the fir st one. In contrast to ACC synthase, ACC oxidase was induced markedly in bo th the first and second layers and the development of its activity and the levels of mRNA remained high until later stages, It was considered that wou nd ethylene was closely associated with the development of ACC oxidase, sin ce 2,5-norbornadiene (NBD), an inhibitor of ethylene action, substantially suppressed it. Phenylalanine ammonia-lyase (PAL) greatly increased in activ ity after wounding similarly to that of ACC synthase, in which increase in PAL activity occurred predominantly in the first layer. Induction of peroxi dase activity after wounding had a close correlation in profile with that o f ACC oxidase in that marked increases in the activity were observed in bot h the first and second layers and were strongly suppressed by NBD applicati on, Four peroxidase isozymes were found by PAGE, among which a fraction was newly detected after wounding.