Ja. Zwar et Pm. Chandler, ALPHA-AMYLASE PRODUCTION AND LEAF PROTEIN-SYNTHESIS IN A GIBBERELLIN-RESPONSIVE DWARF MUTANT OF HIMALAYA BARLEY (HORDEUM-VULGARE L), Planta, 197(1), 1995, pp. 39-48
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.