MECHANISM OF ACTION OF THE DIPHENYL ETHER HERBICIDE ACIFLUORFEN-METHYL IN EXCISED CUCUMBER (CUCUMIS SATIVUS L.) COTYLEDONS
Abstract
By following the efflux of several radiolabelled substances from excised and preloaded cucumber cotyledons, the relative activity of various diphenyl ether herbicides was determined. Acifluorfen-methyl (AFM) had the most herbicidal activity. Damage due to this compound could be detected in relatively short periods of time at low concentrations. I believe these results are indicative of the primary herbicidal activity of these compounds. In this thesis, I have investigated the physiological mechanism of action of AFM. I propose that AFM is activated in light by yellow plant pigments (xanthophylls; e.g., lutein) and then is involved, either directly or indirectly, in the initiation of a free radical chain reaction with the polyunsaturated fatty acid moieties (e.g., linolenic acid) of the phospholipid molecules making up cellular membranes. This hypothesis is based on the facts that (a) AFM is active in green and etiolated tissue in the presence of both 1 (mu)M DCMU and 1 (mu)M DBMIB and inactive in nonpigmented tissue (e.g., roots); (b) lutein is the primary yellow pigment present in etiolated cucumber cotyledons; (c) protection can be obtained by inhibiting carotenoid biosynthesis with 10 (mu)M fluridone; (d) herbicidal injury is expressed as a general increase in membrane permeability at concentrations as low as 10 nM; (e) following activation at 1 (mu)M this increase in permeability can be detected within 10 to 15 min; (f) visual verification of membrane disruption has been made by electron microscopy; (g) incurred herbicidal damage requires light and oxygen; (h) significant increases in thiobarbituric acid-reacting materials, products of lipid peroxide decomposition, can be detected after treatment; and (i) protection against injury can be obtained with a known in vivo lipophilic free radical scavenger, (alpha)-tocopherol.
Degree
Ph.D.
Subject Area
Botany
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