Abstract
Tissue-specific expression of the isoforms of rice α-amylase and their expression in suspension cultured cells were investigated, together with regulation by various sugars. Six isoforms, Y, A, G, H, I and J, were identified: Isof orm A, Isof orm Y and Isof orms A-J were mainly detected in germinating seeds, young plant tissues, and suspension-cultured cells, respectively. From the results of amino acid sequencing of the purified isoforms, isoform A and isoform H were identified as the gene products of RAmy1A and RAmy3D, respectively (Plant Physiol., 110, 1395-1404 (1996)) . Since metabolic regulation of the expression of rice a-amylase has been reported, we analyzed this phenomenon by following the changes in levels of each isoform in cells in suspension cultures in the presence of various sugars . The expression of the RAmy3D-encoded protein (isoform H) was completely repressed by so-called metabolic sugars, while expression of the RAmy1A-encoded protein (isoform A) was repressed to a less extent. The results indicate that high expression of the RAmy3D-encoded protein is controlled much differently from that of the RAmy1A-encoded protein.
