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PLANT PHYSIOLOGY , Vol 114, Issue 1 203-212, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Grain Development Mutants of Barley ([alpha]-Amylase Production during Grain Maturation and Its Relation to Endogenous Gibberellic Acid Content)
L. S. Green, E. M. Faergestad, A. Poole and P. M. Chandler
Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, G.P.O. Box 1600 (L.S.G., E.M.F., P.M.C.)
Barley (Hordeum vulgare L. Himalaya) mutants with altered grain morphology
were isolated to investigate whether defects in grain development, possibly
involving gibberellins (GAs) and abscisic acid, would lead to altered
patterns of [alpha]-amylase gene expression. Following treatment with
sodium azide, 75 mutants, typically showing grain shriveling, were
identified. At grain maturity 15 of the 75 mutants had higher
[alpha]-amylase activities in shriveled grains compared with either
phenotypically normal grains that developed on the same heterozygous plant
or with grains of cv Himalaya. Studies of four of these mutants
demonstrated increased levels of both high- and low-isoelectric point
[alpha]-amylase isozymes midway through grain development. This category of
mutant has been designated pga, for premature grain [alpha]-amylase. One
such mutant (M326) showed an endosperm-determined inheritance pattern. When
crossed into a (GA-deficient) dwarfing background there was a 10- to
20-fold reduction in [alpha]-amylase activity, suggesting a requirement for
GA biosynthesis. Endogenous GAs and abscisic acid were quantified by
combined gas chromatography-specific ion monitoring in normal and mutant
grains of heterozygous M326 plants during the period of [alpha]-amylase
accumulation. Mutant grains had significantly higher (5.8-fold) levels of
the bioactive GA1 compared with normal grains but much lower (approximately
10-fold) levels of the 2[beta]-hydroxylated ("inactive") GAs, typical of
developing barley grains (e.g. GA8, GA34, GA48). We propose that a reduced
extent of 2[beta]-hydroxylation in the mutant grains results in an
increased level of GA1, which is responsible for premature [alpha]-amylase
gene expression.
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