THE ROLE OF ASCORBATE IN DROUGHT-TREATED COCHLEARIA-ATLANTICA POBED AND ARMERIA-MARITIMA (MILL) WILLD

Cochlearia atlantica is a species rich in ascorbic acid. After 4 days of intermittent drought treatment, there was a large decrease in the concentration of ascorbate and glutathione, functioning probably as radical scavengers (antioxidants). Although there was no increase in lipid peroxidation (a marker of oxygen radical damage), drought treatment did result in the destruction of chlorophyll and a decrease in protein. This species showed little or no change in the activities of five enzymes usually associated with the processing of, and protection from, activated forms of oxygen. Armeria maritima showed similar decreases in relative water content and dry weight after droughting, but a quantitatively smaller decrease in ascorbate with no loss of glutathione. Instead a major response to drought, in this species, was the marked increases in the activities of superoxide dismutase and peroxidase. Despite these increases in enzymic defences against oxygen radicals, drought treatment resulted in increased lipid peroxidation in A. maritima. It is concluded that ascorbic acid and glutathione may play a significant role in the response to drought in C. atlantica but protection in A. maritima is largely through enzymic processing of activated forms of oxygen.