Effect of Water Stress on the Chloroplast Antioxidant System

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Abstract
The effect of water stress on glutathione reductase and catalase activities was evaluated in leaf blades of field-grown winter wheat (Triticum aestivum L.). Wheat was sown at 2 seeding rates under both irrigated and dryland conditions. Flag leaves from dryland plants sown at 60 kg/ha showed no change in either glutathione reductase or catalase activities per unit leaf area, while leaves from the basal portion of the canopy exhibited a 273% increase in glutathione reductase activity and a 60% increase in catalase activity. Glutathione reductase activity in dryland plants sown at 120 kg/ha increased 25% in flag leaves and 225% in basal leaves. No change in catalase activity was observed in either flag or basal leaves from these same plants. The increase in glutathione reductase activity in response to water stress was observed when activity was expressed on either a per unit leaf area, protein or chlorophyll basis. No change in catalase activity was detected when enzyme activity was expressed on a protein basis.