Aleurones from a Barley with Low [alpha]-Amylase Activity Become Highly Responsive to Gibberellin When Detached from the Starchy Endosperm.
The physiological and molecular bases for contrasting [alpha]-amylase phenotypes were examined in germinating seeds of two barley (Hordeum vulgare L.) cultivars, Morex and Steptoe. Morex is a high-quality malting barley that develops high [alpha]-amylase activity soon after germination. Steptoe is a feed barley that develops only low [alpha]-amylase activity levels during this period. The expression of all high- and low-isoelectric point (pl) [alpha]-amylase isozymes is reduced in Steptoe. The amount of [alpha]-amylase mRNA per gram of seedling tissue is correspondingly lower in Steptoe. Southern blot analysis revealed that the cultivars have the same copy number and organization for most high- and low-pl genes. Steptoe seedlings or embryoless half-seeds produce little [alpha]-amylase in response to exogenous applications of gibberellic acid (GA3) compared with Morex. However, when isolated aleurones of both cultivars are treated with GA3, they produce similar amounts of high- and low-pl [alpha]-amylase RNAs. This suggests that a factor in the starchy endosperm is responsible for lowered [alpha]-amylase response in Steptoe. The factor is probably not abscisic acid (ABA), since the two cultivars have similar concentrations of ABA during germination.
Skadsen
R. W.
RW
United States Department of Agriculture, Agricultural Research Service, Cereal Crops Research Unit, 501 North Walnut Street, Madison, Wisconsin 53705.