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 with gibberellic acid (GA3) restored growth to levels of the tall parent. alpha-Amylase production was examined in germinated grains of the dwarf mutant and in Himalaya plants treated with gibberellin (GA) biosynthesis inhibitors. The mutant showed reduced alpha-amylase activity relative to the parent when grains were germinated on water, but activities were equivalent to the parent following germination on GA3 solution. Germination of normal or mutant grains in the presence of GA biosynthesis inhibitors led to reduced alpha-amylase activity levels, but normal levels were restored if GA3 was included in the inhibitor solution. These data are consistent with a model in which alpha-amylase production in the germinated grain is regulated by the supply of active GA3. Treatment of M117 with GA3 increased the length fresh weight, dry weight, volume, cell number, and protein content of the first leaf. Proteins being synthesized in the first leaf were labelled with [35S]methionine and fractionated by two-dimensional electrophoresis. No reproducible qualitative or quantitative differences in protein profiles were detected in response to GA3 treatment. In contrast, first leaves from seedlings exposed to dehydration stress had profiles clearly distinguishable from those of control seedlings. Stem sections from dwarf plants maintained on 10 micromolar GA3 in the presence of sucrose elongated significantly more than controls without GA3, but two-dimensional analysis of the [35S]methionine-labelled radioactive polypeptides again revealed no GA3-induced differences. It was concluded that enhanced elongation rates of leaves or stem segments were not associated with major changes in gene expression.