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

The activities of several enzymes involved in plant protection against stress were assayed to determine 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 leafy spurge plants were heat (41 degrees C up to 48 h), cold (5 degrees C up to 25 days), drought (up to 5 days) 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 imposed and the times of exposure. The effects on the specific activity of glutathione S-transferase in plants 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 reductase specific activity decreased slightly with heat, nearly doubled with cold, 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, increased very slightly during drought, and increased in beetle-fed plants. Ascorbate peroxidase specific activity increased with the high temperature, was significantly higher only at 3 days during drought but returned to control 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 not 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 degrees C for 1 day.