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Title: ANTAGONISM OF OXIDATIVE STRESS INDUCED BY DICLOFOP-METHYL IN SUSCEPTIBLE LEAFY SPURGE

Author
item Shimabukuro, Richard
item Hoffer, Barry
item BIEWER, KRISTI - NORTH DAKOTA STATE UNIV.
item Davis, David

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The possibility that some weed control methods result in the production of phytotoxic oxidations products was investigated in the perennial noxious weed leafy spurge (Euphorbia esula L.). Diclofop-methyl (DM) and 2,4-D sprayed onto 6- to 8-week-old plants of leafy spurge caused the older leaves to senesce; young leaves and apices remained healthy. The phytotoxicity of DM was reversed by the antioxidant vitamin E in these plants and in whole plants of DM-susceptible oat. Ethylene often indicates adverse effects of various treatments, and of senescence. DM or the auxinic compound 2,4-D increased ethylene formation in mature leaves of leafy spurge. DM-induced ethylene was reduced by about 50% when DM was mixed with vitamin E, but 2,4-D-induced ethylene was not. DM did not increase ethylene formation in DM-resistant pea or tobacco. Ethylene evolution in DM-resistant tobacco also was not changed by DM, but 2,4-D induced a 3-fold increase over controls. 2,4-D appears to act at a site different from that of DM in the pathway of ethylene formation. Ethylene formation increased in DM-treated susceptible biotypes of annual ryegrass and wild oat but not in DM-resistant biotypes. DM also reduced root and shoot formation and dry weight in hypocotyl segments of dark-grown sterile leafy spurge seedlings. Organ formation and dry weights were increased over controls by combining DM with antioxidants; vitamin E was more effective than vitamin C. These results support the concept that DM induces oxidative stress in susceptible plant tissues, and the presence of antioxidants prevents the formation and/or action of the phytotoxic free radicals.

Technical Abstract: Diclofop-methyl (DM) sprayed onto 6 to 8-week-old plants of leafy spurge (Euphorbia esula L.) caused senescence and abscission of older leaves, but the young leaves and apex remained healthy. The phytotoxicity of DM was reversed by the antioxidant, alpha-tocopherol, in leafy spurge and in whole plants of DM susceptible oat (Avena sativa L. cv. Gary). DM or 2,4-D increased ethylene in mature leaves of leafy spurge. DM-induced ethylene was reduced by about 50% when DM was applied with alpha-tocopher- ol, but the 2,4-D-induced ethylene was not. DM did not increase ethylene in DM-resistant pea or tobacco, but 2,4-D induced a 3-fold increase in ethylene evolution over controls in DM-resistant tobacco. 2,4-D appears to act at a site different from that of DM in the pathway of ethylene formation. Ethylene evolution increased in DM-treated susceptible biotypes of annual ryegrass (Lolium rigidum L.) and wild oat (Avena fatua L.) but not in resistant biotypes. DM reduced root and shoot formation and dry weight in hypocotyl segments of etiolated leafy spurge seedlings grown in vitro. Organogenesis and dry weights were increased over controls by the combination of DM + antioxidants; alpha-tocopherol was more effective as an antioxidant than ascorbic acid. These results support the concept that DM induces oxidative stress in susceptible plant tissues, and the presence of antioxidants reduces the damaging action of the phytotoxic free radicals.