Activity of stress-related enzymes in the perennial weed leafy spurge (Euphorbia esula L.)

The activities of several enzymes involved in plant protection against stre ss were assayed to determine physiological aspects of the perennial noxious weed leafy spurge (Euphorbia esula L.) that might render the plant vulnera ble to integrated pest management procedures. Stresses imposed on leafy spu rge plants were heat (41 degreesC up to 48 h), cold (5 degreesC up to 25 da ys), drought (up to 5 days) and feeding by a flea beetle (Aphthona lacertos a), a biocontrol insect used for control of leafy spurge (1- and 2-day feed ings). The effects varied with the stress imposed and the times of exposure . The effects on the specific activity of gluthathione S-transferase in pla nts exposed to the four stresses were: more than doubled in heat, remained at essentially control levels in the cold, increased by 50% during drought, and increased by 20% or less in flea beetle-fed plants. Glutathione reduct ase specific activity decreased slightly with heat, nearly doubled with col d, increased almost 60% during drought, and remained essentially unchanged in beetle-fed plants. Catalase-specific activity decreased in plants under all four stresses. The specific activities of superoxide dismutase remained essentially constant in plants exposed to heat, increased in the cold, inc reased very slightly during drought, and increased in beetle-fed plants. As corbate peroxidase specific activity increased with the high temperature, w as significantly higher only at 3 days during drought but returned to contr ol levels or below by 5 days, and was greatly inhibited in flea beetle-fed plants. The effects of cold on ascorbate peroxidase-specific activity are n ot well defined. Initial experiments indicated little change up to 24 days, but subsequent experiments resulted in a significant decrease at 25 days, with recovery closer to control levels in plants returned to 25 degreesC fo r 1 day. Published by Elsevier Science B.V.