VARIATION IN THE ANTIOXIDANT METABOLISM OF DROUGHT-TOLERANT AND DROUGHT-SUSCEPTIBLE VARIETIES OF SORGHUM-BICOLOR (L) MOENCH - EXPOSED TO HIGH-LIGHT, LOW-WATER AND HIGH-TEMPERATURE STRESS

Seedlings of four varieties of Sorghum bicolor differing in drought tolerance under field conditions were exposed to three components of drought stress in the laboratory. They were exposed to high light (10,000 lux), high temperature (36 +/- 2 degrees C), and low water stress (-0.5 MPa) in different experiments. After 72 hours of exposure to each of these stresses, changes in lipid peroxidation, and the activities of catalase, superoxide dismutase and guaicol dependent peroxidase were assayed. Out of the four varieties, CSV-5, which is a drought susceptible variety, showed maximum increases in the level of malondialdehyde, which is a product of lipid peroxidation, under all three stress conditions. IS-22380, PA-59 and E-36 showed lesser lipid peroxidation. Superoxide dismutase and catalase activities increased in the drought tolerant varieties. While IS-22380 seemed to adapt to stress conditions by manipulating the catalase levels, E-36 showed higher adaptability by manipulating the superoxide dismutase levels under water and temperature stress. Adaptation to light stress was manifested by increases in the levels of superoxide dismutase in the drought tolerant varieties. Thus, a drought tolerant variety can adapt to drought stress by diverse manipulations in the antioxidant system.