*3.3. Effects of High-Ca Treatment on the Activities of Key Enzymes Involved in Glucose Metabolism* 3.3.1. AI

The changes in AI activity are shown in Figure 2a. The AI activity of the CK group first increased, then decreased and increased again. Finally, there was no significant difference between the CK group and the high-Ca treatment group. The AI activity of the high-Ca treatment group showed a single-peak curve, and the highest peak occurred at 64 d after anthesis; this peak was significantly lower and occurred earlier than that of the CK group. There was no significant difference in AI activity between the high-Ca treatment group and CK group at 64 d after anthesis. These results indicated that high-Ca treatment inhibited AI activity in the early stage of sugar accumulation, thus inhibiting the accumulation of reducing sugars.

**Figure 2.** Effects of high-Ca fertilizer on the activities of key enzymes involved in fructose metabolism: (**a**) AI; (**b**) NI; (**c**) SS-I; (**d**) SS-II; (**e**) SPS. (**f**) The net activity of sucrose invertase in the synthetic direction. Note: The symbols with \* in the figure indicate significant differences between the CK and high-Ca treatments for the same data type; otherwise, there was no significant difference.
