Abstract
Identifying the mechanisms regulating starch remobilization after heading in rice leaf sheaths is essential to understand the capability of the source for grain filling. In the present study, the changes in starch content and expression levels of α-amylase genes in the third leaf sheaths of Takanari, a high-yielding indica cultivar, were compared with those of Nipponbare, a standard japonica cultivar, during the post-heading stage to examine the starch remobilization characteristics in the leaf sheath of a high-yielding cultivar. Starch content in Takanari tended to decrease at a faster rate than in Nipponbare starting 3 days after heading. The decrease in starch content during 12 days after heading was greater in Takanari than in Nipponbare. Of eight genes predicted to encode α-amylase in the rice genome, RAmy2A and RAmy3C were primarily expressed in the leaf sheaths after heading. Moreover, RAmy2A mRNA level peaked at 9 days after heading in both cultivars. Particularly in Takanari, the RAmy2A mRNA levels rapidly increased from 3 to 9 days after heading. In addition, α-amylase activity was significantly higher in Takanari than in Nipponbare at 9 days after heading. Our results suggest that the rapid degradation of starch in the leaf sheaths of Takanari at the post-heading stage may be attributed, at least in part, to the enhancement of α-amylase activity caused by an increase in RAmy2A transcription level.
