ARS | Publication request: DIFFERENTIAL EXPRESSION OF ALPHA-AMYLASE ISOZYMES IN BARLEY

Submitted to: Isozymes International Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 9, 1996
Publication Date: N/A

Technical Abstract: The proper expression of the alpha-amylase isozymes in germinating barley is critical to the malting and brewing industries. The high-pI isozyme begins to appear two days from the onset of imbibition while the low-pI isozyme appears later. By day 5, the high-pI isozyme accumulates to levels 5 to 10-fold greater than the low-pI isozyme. In contrast, expression in isolated aleurones is dominated by the low-pI isozyme. However, the high-pI isozyme is produced and secreted at much lower levels, relative to the low-pI isozyme. Studies were conducted to determine why isozyme expression differed between the two systems. The starchy endosperm was found to strongly influence expression. When deembryonated half-seeds were left untreated, the activities of both isozymes increased steadily each day, with the low-pI isozyme predominating, but little alpha-amylase was secreted. When gibberellin hormone (GA) was applied, high-pI isozyme activity increased rapidly and dominated the system, and secretion was very strong. Isolated aleurones were also incubated in thick homogenates of the starchy endosperm of half-seeds. Similar results were found. Northern blot analysis revealed that the endosperm probably caused greater levels of the high-pI isozyme to be produced by prolonging the rise in high-pI mRNA levels. It is proposed that an interaction of GA (directly or indirectly) and components of the starchy endosperm produce the high- and low-pI isozyme expression patterns seen in intact barley seedlings.