Abstract
Starch is a major and important storage material for energy and carbon source in plants. Transient starch synthesized in leaf chloroplast during the day was degraded at night. Despite what this is one of the major metabolic fluxes in plant, there still exist several arguments against the pathway of starch remobilization from the plastids in living cells. α-Amylase is known to be the only enzyme that can digest intact starch granules. We analyzed starch contents in transgenic rice leaves in which the rice predominant α-amylase isoform I-1 was co-suppressed or overexpressed. The results indicated that the starch accumulation reversely corelated to level of α-amylase I-1 expression. Immunocytochmical analysis and expression and targeting of α-amylase I-1/GFP fused proteins revealed that a well-known secretory glycoprotein α-amylase I-1 occurs in chloroplasts. We will discuss a mechanism of starch degradation in rice chloroplasts, particularly access of α-amylase to plastidial starch.
