Abstract
With the aim of determining the level at which ageing exerts its effect on the expression of α-amylase, GA3 regulation of α-amylase production was studied in isolated aleurone layers from aged wheat seeds. GA3-induced α-amylase activity was lower in the tissue from aged seeds than in controls. However, the proportion of 35S-methionine incorporated into α-amylase was higher in the aged than in control tissue. The pattern of α-amylase isoforms was resolved by isoelectric focusing and showed that two isogroups were present with the activity of the high-pI isogroup being higher in the control than in the aged lot. These apparently contradictory results may be explained in terms of differences in isozyme expression. Studies on the expression of α-amylase genes indicated a reduction in the level of high-pI mRNA in aged tissue. Dose-response curves showed lower GA3-responsiveness of aleurone layers from aged seeds as compared to the controls. From these results, it is proposed that the diminished capacity of α-amylase production in aleurone from aged seeds is apparently due to a decrease in the expression of the high-pI α-amylase genes, and this reduction is associated with a decrease in the response to GA3. Key words: Seed ageing, wheat aleurone, gibberellic acid, α-amylase isozymes, gene expression.
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