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 degrees C), drastically reduced the biosynthesis of alpha-amylase as determined by the incorporation of [(35)S]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 alpha-amylase are distinguishable in their temperature dependency. At the higher temperature regime (>==40 degrees C), the complex-type alpha-amylase isoform, resistant to hydrolytic digestion by endo-beta-N-acetylglucosaminidase H (Endo-beta-H) was predominantly secreted, whereas at lower temperatures (<==15 degrees C), the isoform susceptible to Endo-beta-H attack was the major molecular form secreted.