Regulation of α-amylase formation and gene expression in the developing wheat embryo : Role of abscisic acid, the osmotic environment and gibberellin.

Embryos in developing wheat (Triticum aestivum L., cv. Sappo) grains (15-40 d post anthesis, dpa) contain no detectable α-amylase. When isolated from the grain they produce the enzyme even though they do not germinate. Younger (15 dpa) and older (45 dpa) embryos produce only a group of isozymes of low isoelectric point (pI): at intermediate ages low-pI and high-pI groups appear. The low-pI group is formed first, about 6 h after isolation, followed by the high-pI group at 16h. The formation of high-pI isoenzymes is prevented by abscisic acid and osmoticum, which also suppress the accumulation of high-pI mRNA. Almost all of the low-pI isoenzymes are unaffected by these two factors. Low-pI mRNA transcripts are present in embryos in situ but are not translated. Translation occurs when embryos are isolated, though there appears to be no further accumulation of low-pI mRNA. Addition of gibberellic acid to isolated embryos causes a great increase in accumulated high-pI mRNA, but only a small increase in low-pI message. Added gibberellic acid enables younger and older embryos to produce high-pI isoenzymes. The regulation of α-amylase gene expression and enzyme formation in developing embryos in situ is discussed in the light of these findings.