INACTIVATION OF STRESS-INDUCED 1-AMINOCYCLOPROPANE CARBOXYLATE SYNTHASE INVIVO DIFFERS FROM SUBSTRATE-DEPENDENT INACTIVATION INVITRO

The activity of 1-aminocyclopropane carboxylate (ACC) synthase increased rapidly in tomato (Lycopersicon esculentum Mill.) leaf discs after vacuum infiltration, reached a maximum after about 30 minutes, and subsequently decayed with an apparent half-life of about 20 minutes. Aminoethoxyvinylglycine, a known inhibitor of ACC synthase, did not alter the apparent turnover of ACC synthase in vivo although it efficiently blocked inactivation of the enzyme by its substrate S-adenosylmethionine in vitro. Similar results were obtained, using a novel assay with permeabilized cells, for ACC synthase in tomato cell cultures treated with a fungal elicitor. The results indicate that inactivation of ACC synthase in vivo differs from substrate-dependent inactivation in vitro.