Preferential secretion of R-type alpha-amylase molecules in rice seed scutellum at high temperatures

Exposure of fresh scutella excised from 4-day-old rice seedlings to higher temperatures, (40-42°C), drastically reduced the biosynthesis of α-amylase as determined by the incorporation of [³⁵S]methionine into the immunoprecipitable product. However, the intracellular transport and extracellular secretion of the enzyme molecules were enhanced at high temperatures, indicating that the biosynthesis and secretion of α-amylase are distinguishable in their temperature dependency. At the higher temperature regime (40°C), the complex-type α-amylase isoform, resistant to hydrolytic digestion by endo-β-N-acetylglucosaminidase H (Endo-β-H) was predominantly secreted, whereas at lower temperatures (15°C), the isoform susceptible to Endo-β-H attack was the major molecular form secreted.