ALPHA-AMYLASE PRODUCTION AND LEAF PROTEIN-SYNTHESIS IN A GIBBERELLIN-RESPONSIVE DWARF MUTANT OF HIMALAYA BARLEY (HORDEUM-VULGARE L)

A dwarf mutant, M117, was isolated following sodium-azide mutagenesis of barley (Hordeum vulgare L. 'Himalaya'). Treatment of the mutant wit h gibberellic acid (GA(3)) restored growth to levels of the tall paren t. alpha-Amylase production was examined in germinated grains of the d warf mutant and in Himalaya plants treated with gibberellin (GA) biosy nthesis inhibitors. The mutant showed reduced alpha-amylase activity r elative to the parent when grains were germinated on water, but activi ties were equivalent to the parent following germination on GA(3) solu tion. Germination of normal or mutant grains in the presence of GA bio synthesis inhibitors led to reduced alpha-amylase activity levels, but normal levels were restored if GA(3) was included in the inhibitor so lution. These data are consistent with a model in which alpha-amylase production in the germinated grain is regulated by the supply of activ e GAs. Treatment of M117 with GA(3) increased the length, fresh weight , dry weight, volume, cell number, and protein content of the first le af. Proteins being synthesized in the first leaf were labelled with [S -35]methionine and fractionated by two-dimensional electrophoresis. No reproducible qualitative or quantitative differences in protein profi les were detected in response to GA(3) treatment. In contrast, first l eaves from seedlings exposed to dehydration stress had profiles clearl y distinguishable from those of control seedlings. Stem sections from dwarf plants maintained on 10 mu M GA(3) in the presence of sucrose el ongated significantly more than controls without GA(3), but two-dimens ional analysis of the [S-35]methionine-labelled radioactive polypeptid es again revealed no GA(3)-induced differences. It was concluded that enhanced elongation rates of leaves or stem segments were not associat ed with major changes in gene expression.