EFFECTS OF PLANT-GROWTH REGULATORS ON THE ANTIOXIDANT SYSTEM IN CALLUS OF 2 MAIZE CULTIVARS SUBJECTED TO WATER-STRESS

The effects of brassinolide, uniconazole and methyl jasmonate on sever al aspects of antioxidant defences, were studied in callus tissues of drought-resistant (PAN 6043) and drought-sensitive (SC 701) cultivars of maize. When regulator-treated calli were subjected to water stress with PEG for 24 h the activities of antioxidant enzymes, such as super oxide dismutase, catalase, ascorbate peroxidase, peroxidase and glutat hione reductase, remained higher in callus of the drought-resistant th an in callus of the drought-sensitive cultivar. Damage, as indicated b y the levels of hydrogen peroxide and malondialdehyde, the reduction o f ascorbate and carotenoids, and leakage of electrolytes from cells wa s apparent in callus of both cultivars as a consequence of the applied water stress. However, the damage was less marked in the drought-resi stant cultivar. The regulator-treated callus of this cultivar also had a higher survival percentage than that of the drought-sensitive culti var. The present results also compare the effects of growth regulators on antioxidant systems in callus tissue of different drought-resistan t cultivars when exposed to paraquat and water stress.