The Effects of 2,5-Norbornadiene on the Induction of the Activity of 1-Aminocyclopropane-l-carboxylate Synthase and of Phenylalanine Ammonia-lyase in Wounded Mesocarp Tissue of Cucurbita maxima

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Abstract
Activities of both 1-aminocyclopropane-l-carboxylate (ACC) synthase and phenylalanine ammonia-lyase (PAL) were rapidly induced in excised mesocarp discs of Cucurbita maxima Duch. The increase in activity of ACC synthase preceded that of PAL. 2,5-Norbornadiene (NBD), an inhibitor of the action of ethylene [Sisler and Yang (1984) Phytochemistry 12: 2765-2768.], enhanced the level of activity of ACC synthase in excised mesocarp disc and overcame the suppression by exogenous ethylene. NBD, by contrast, suppressed the level of PAL activity induced in the wounded tissue. These results suggest that endogenous ethylene produced in the wounded mesocarp tissue suppresses the induction of ACC synthase but promotes the induction of PAL.