Author
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Davis, David |
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SWANSON, HARLEY - RETIRED ARS |
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Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/1/2001 Publication Date: N/A Citation: N/A Interpretive Summary: Five key enzymes involved in protecting plants against environmental stress and insect attack were analyzed to determine some of the changes that occur in the perennial weed, leafy spurge, upon exposure to the heat, cold, drought and feeding by a flea beetle. The flea beetle is presently being used in a biocontrol program for the control of leafy spurge. The enzymes assayed include glutathione S-transferase (GST), glutathione reductase (GR), ascorbic acid peroxidase (APOX), catalase (CAT) and superoxide dismutase (SOD) which are all involved directly or indirectly in mechanisms of combating damage to plant tissues caused by reactive oxygen species, a process commonly known as oxidative stress. The results varied according to the particular stress imposed and on the enzyme analyzed. CAT was the most consistent in that its activity decreased with all four stresses. GST, which utilizes glutathione, and GR, which maintains glutathione in the most effective chemical form, had their activities syncronized in a direct relationship only in drought- stressed plants. SOD activity increased in flea beetle-fed plants and only slightly under drought stress. APOX activity was the most inconsistent so that definitive conclusions are not yet possible. It is expected that such research will eventually lead scientists and weed control experts to find new and innovative ways to apply for the control of this economically important weed of non-crop lands. Technical Abstract: The activities of enzymes involved in plant protection against stress were assayed for physiological aspects of the perennial noxious weed leafy spurge (Euphorbia esula L.) that might render the plant vulnerable to integrated pest management procedures. Stresses imposed on the plants were: heat (41 C up to 48 h), cold (5 C up to 25 d), drought (up to 5 d) and feeding by a flea beetle (Aphthona lacertosa) a biocontrol insect used for control of leafy spurge (1 and 2 day feedings). The effects varied with the stress and time of exposure. The specific activity of gluthathione S-transferase more than doubled in heat, with almost no change in the cold, increased by 50% during drought and by 20% or less in flea beetle-fed plants. Glutathione reductase specific activity decreased with heat, nearly doubled with cold, increased almost 60% during drought, and was almost unchanged in beetle-fed plants. Catalase specific activity decreased under all four stresses. The specific activity of superoxide dismutase remained essentially constant in heat, increased in the cold, increased very slightly during drought, and increased in beetle-fed plants. Ascorbate peroxidase specific activity increased with high temperature, was higher only at 3 d during drought but returned to control levels or below by 5 d, and was greatly inhibited in flea beetle-fed plants. The effects of cold on ascorbate peroxidase-specific activity are not well defined. Initial experiments indicated little change by 24 d, but later experiments resulted in large decreases at 25 d, with recovery closer to control levels in plants returned to 25 C for 1 d. |
