Sucrose Synthesis in Flag Leaves and Sucrose Degradation in Grains After Anthesis of Wheat

The activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) in wheat flag leaves and that of SS in grains were examined with HPLC and enzymological methods. The relations of these enzymes to photosynthetic rate of flag leaves and filling rate of grains were also analyzed. The results showed that the activity of SPS in flag leaves maintained a high level within 14 d after anthesis(Fig.1), while that of SS kept high from 14 d to 28 d after anthesis(Fig.2). The sucrose content of flag leaves was positively correlated with leaf photosynthetic rate. Within 28 d after anthesis(Fig.3), the activity of SS in grains kept high (Fig.4), and the sucrose content of grains significantly decreased correspondingly (Fig.5). The activity of SPS in flag leaves showed a significant positive correlation with leaf photosynthetic rate(Fig.7). In contrast, the activities of SS in flag leaves and in grains were highly positively correlated with the rate of starch accumulation in grains (Fig.9). Sucrose synthesis and degradation in Lumai 22 were much higher than those of Yannong 15, indicating marked genotypic differences of sucrose-metabolizing-enzymes between the two wheat cultivars.