FIGURE 7
The activities of the four enzymes in relation to starch synthesis in grain exhibited variable responses to stresses (Figure 8). Compared with CK, sucrose invertase activity was decreased by 30% in DS, 41% in HS and 30% in DHS on the 10th DAP for superior grain. For inferior grain, it was reduced by 57% in DS, 40% in HS and 51% in DHS. Similar or even higher sucrose invertase activity was observed on the 25th DAP in stress treatments (Figure 8a). For sucrose synthase activity, it was decreased by 30-45% on the 10th DAP and by 28-39% on the 25thDAP for superior grain in stress treatments. For inferior grain, it was decreased by 19-21% on the 10th DAP in stress treatments (Figure 8b). For ADP Glc pyrophosphorylase activity, it was decreased by 21-67% on the 10th DAP and by 16-50 % on the 25th DAP for superior grain in the stress treatments compared with CK. For inferior grain, lower ADP Glc pyrophosphorylase activity was observed in both DS and DHS treatments (Figure 8c). For starch synthase activity, it was decreased by 22-34% on the 10th DAP in stress treatment for superior grain (Figure 8d).