α-Amylase production and leaf protein synthesis in a gibberellin-responsive dwarf mutant of ‘Himalaya’ barley (Hordeum vulgare L.)

Abstract

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, α-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 α-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 α-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 α-amylase production in the germinated grain is regulated by the supply of active GAs. 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 μM 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.