Wound-Induced ACC Synthase, an Immunochemical Comparison of the Wound-Induced and Auxin-Induced Enzymes

Abstract

Ethylene biosynthesis in higher plants is developmentally regulated and its rate changes transiently in various tissues at certain stages of plant development. Hook and plumule opening of dicot seedlings, leaf or fruit abscission, leaf or flower petal senescence and fruit ripening are associated with changes in the ethylene production rate [1]. At least in vegetative tissues, elevated cellular concentration of auxin increases the ethylene biosynthetic rate, and the other PGRs such as cytokinins and ABA regulate auxin action [9]. The biosynthetic rate of ethylene is also greatly changed by various environmental stimuli that are irregularly imposed upon plants, and tissue wounding, for example, causes a remarkable increase in ethylene production in many tissues [9, 13]. In both cases, ethylene is formed by enzymatic cleavage of ACC which is produced from S-adenosyl-methionine by ACC synthase. The rate of ethylene biosynthesis is well correlated with the endogenous activity of ACC synthase [5, 8, 14], and this enzyme plays a role as the rate-limiting enzyme in ethylene biosynthesis [13]. Thus, cellular activity of ACC synthase can be increased by two very different stimuli; auxin, a chemical stimulus and tissue wounding, a physical stimulus. Studies with inhibitors of RNA and protein synthesis [15] and with density labeling [2] have suggested that the increased enzyme activity was due to de novo synthesis of the enzyme protein.