GIBBERELLIN ANTAGONIZES PACLOBUTRAZOL-INDUCED STRESS PROTECTION IN WHEAT SEEDLINGS

Gibberellic acid (GA) antagonism of the growth inhibitory and stress p rotective effects of paclobutrazol (P) was investigated in wheat seedl ings (Triticum aestivum L. cv Katepwa). Seeds were imbibed for 12h in aqueous solutions of 0.1% ethanol (control), 100 mg . L-1 P, 50 mg . L -1 GA and a combination of both. Seeds were air dried, planted and gro wn for 10 d. The growth inhibitory effects of P were reversed by GA wh ereas the combination of GA and paclobutrazol resulted in height and f resh mass values similar to the control. Heat stress decreased fresh m ass, chlorophyll and carotenoid levels and increased electrolyte leaka ge of wheat leaves while paraquat induced chlorosis in excised leaf se gments. These symptoms of injury were alleviated by P while seedlings treated with a combination of P and GA were nor significantly differen t from the control. Changes in protein expression were investigated in an attempt to understand the basis of P-induced stress protection. Ba sed on optical densities, protein expression was either increased or d ecreased by P. Similar trends were observed with GA and the combinatio n of P and GA where the degree of the quantitative change appeared to be independent of the treatment. Qualitatively, two new acidic, 41.4 a nd 53.7ku, and several other proteins, ranging from 54-56 ku, were ind uced by each of the treatments, bur not in the control. No proteins we re detected exclusively in the P treatment and subsequently removed by simultaneous treatment with GA and P. The abundance of proteins expre ssed by either P or GA may have interfered with the identification of specific proteins associated with P-induced stress protection.