4.4. RS and starch enzymes
Many studies have indicated that the activities of the enzymes
participating in the growth of rice grains peak during the earlier
stages and then start to decrease (Chen et al., 2001; Hirose &
Terao, 2004). Our results were consisted with the previous reports
(Fig. 4)
AGP is the first enzyme to synthesise the precursor for starch
formation and elongates glucose polymers through the formation
of a-1,4-bonds by other enzymes, such as SS (Hannah, 2007). This
enzyme catalyses the first committing step in this pathway, and its
allosteric properties are essential for the control of the rates of
starch biosynthesis (Jeon et al., 2010). An enhanced AGP activity
can increase the seed weight. For example, rice overexpressing
Escherichia coli AGPase exhibited an up to 11% increase in seed
weight (Sakulsingharoj et al., 2004). The lower activities of AGP
in MR1 and MR4 indicates that starch synthesis throughout the
grain filling process in high-RS rice is not as effective as the
synthesis of starch in low-RS common rice.