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 (pI) 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-pI 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-pI 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