The effects of gamma-radiation and 2-chloroethyl trimethyl ammonium chloride on biosynthesis of ent(-)kaurene in germinating wheat

Abstract

The effect of gamma-radiation (doses ranging from 0.2 to 2kGy) on in vitro synthesis of ent(-)kaurene was investigated using a partially purified ent(-)kaurene synthetase preparation from germinating wheat endosperms. Incorporation of 2- 14C-mevalonic acid (MVA) into ent(-)kaurene reaches a maximum at 56 hr of germination in all the samples, but the rate decreases with increasing radiation dose. Similarly, biosynthesis of gibberellin (GA) in seeds, imbided with 2- 13C-MVA, is reduced by about 50%, whereas its biological activity is only 2% of control at 2 kGy. This may be attributed to higher sensitivity of the biosynthesis of GA 3, the most biologically active GA derivative in wheat. This reduction in GA synthesis is accompanied by a concomitant accumulation of intermediate precursors, GA 4 and GA 7, in irradiated wheat seedlings. These results indicate that radiation treatment reduces the efficiency of interconversion of a less active GA to a highly active one. Pre-treatment of seeds with 2-chloroethyl trimethyl ammonium chloride (CCC) inhibits ent(-)kaurene synthesis in vitro, but only at high concentrations. Similarly, CCC inhibits GA synthesis in vivo and accentuates the radiation induced damage in wheat seedlings.