MECHANISM OF GENE INDUCTION IN ETHYLENE BIOSYNTHETIC PATHWAY BY HERBICIDES

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Although the auxin-type are considered to herbicides act like natural auxins in plants and their stimulation of ethylene biosynthesis is assumed to be involved in the phytotoxic action of the herbicides, their precise action mechanism is still enigma. The objectives of this study were to clarify the mode of action of auxin-type herbicide quinclorac on susceptible gramineous plants and the mechanisms of gene induction involved in ethylene synthesis.Quinclorac treatment to corn (Zea mays cv. Honey Bantam) roots significantly stimulated ethylene evolution from shoots especially under light irradiation. Moreover, bleaching of leaves and decrease of water content was detected only in the light. Involvement of light for the phytotoxic action was unique to quinclorac and not observed with other auxin-type herbicides such as 2,4-D.Ethylene evolution was also affected by ambient temperature during the herbicide treatment.In this research, we found that ACC synthase, one of key enzymes of ethylene synthesis was significantly induced by quinclorac only in the light. Therefore induction of this enzyme is considered to be main factor of increased ethylene evolution. From the pattern of the induction, involvement of wound-inducible type ACC gene by the herbicide in the light was suggested. Investigation on the induced gene is now in progress.