Gibberellin antagonizes paclobutrazol-induced stress protection in wheat seedlings

Gibberellic acid (GA) antagonism of the growth inhibitory and stress protective effects of paclobutrazol (P) was investigated in wheat seedlings (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 grown for 10 d. The growth inhibitory effects of P were reversed by GA whereas the combination of GA and paclobutrazol resulted in height and fresh mass values similar to the control. Heat stress decreased fresh mass, chlorophyll and carotenoid levels and increased electrolyte leakage of wheat leaves while paraquat induced chlorosis in excised leaf segments. These symptoms of injury were alleviated by P while seedlings treated with a combination of P and GA were nor significantly different from the control. Changes in protein expression were investigated in an attempt to understand the basis of P-induced stress protection. Based on optical densities, protein expression was either increased or decreased by P. Similar trends were observed with GA and the combination of P and GA where the degree of the quantitative change appeared to be independent of the treatment. Qualitatively, two new acidic, 41.4 and 53.7ku, and several other proteins, ranging from 54-56 ku, were induced by each of the treatments, bur not in the control. No proteins were detected exclusively in the P treatment and subsequently removed by simultaneous treatment with GA and P. The abundance of proteins expressed by either P or GA may have interfered with the identification of specific proteins associated with P-induced stress protection.