Induction of 1-Aminocyclopropane-l-carboxylic Acid Synthase in Wounded Mesocarp Tissue of Winter Squash Fruit and the Effects of Ethylene

1-Aminocyclopropane-l-carboxylic acid (AGC) synthase activity increased rapidly after wounding of mesocarp tissue of winter squash fruit [Cucurbita maxima Duch.) and reached a peak at 16 h after excision and then declined sharply. The rise in ACC synthase activity wai followed by increases in the endogenous ACG content and the rate of ethylene production. The activity of ethylene forming enzyme (EFE) also increased rapidly in the excised discs of mesocarp of winter squash fruit. ACG synthase activity was strongly inhibited by aminoethoxyvinylglycine with a Ki value of 2.1 /in. Michaelis-Menten constant of ACC synthase for S-adenosylmethio-nine was 13.3 /at. Ethylene suppressed the induction of ACC synthase in the wounded mesocarp tissue. The suppression by ethylene increased with the increasing concentrations of applied ethylene and the maximum effect was obtained at about 100 /jl I"1 ethylene, at which point the induction was suppressed by 54%. Ethylene did not inhibit ACC synthase activity, nor did it suppress the induction of EFE, but rather it slightly enhanced the latter