Dynamic Changes of Activities of Key Enzymes Involved in Sucrose Metabolism during Grain Filling in Wheat and the Relationship with Starch Accumulation in Grain

Sucrose and starch are the main product of wheat photosynthesis. During sucrose metabolism, Sucrose phosphate synthase (SPS) is the key enzyme controlling sucrose synthesis, but sucrose synthase (SS) is the key enzyme controlling sucrose degradation. In the present experiment conducted in cement cultural pool, three winter wheat (Triticum aestivum L.) cultivars GC8901 (strong gluten), YM49 (medium gluten) and LM1 (weak gluten) were used to investigate the activities of the key enzymes involved in sucrose metabolism in leaf, sheath, ear stem and grain during grain filling and the relationship with starch accumulation in grain. Ten main tillers of each plot were sampled at 6, 12, 18, 24, 30, and 36 days after anthesis, and partitioned into flag leaf, sheath of flag leaf, and ear stem.One hundred grains of each plot were sampled from the spikes from which only two basal grains of the 4th to 12th spikelets were collected. Half of the plant samples were used to determinate the enzyme activities, and the other half for starch content measurement.In the three cultivars, the dynamic changes of activities of sucrose phosphate synthase(SPS) and sucrose synthase(SS) in leaf, sheath, ear stem and grain during grain filling period all fit the single-peak curve. The SPS activity in flag leaf, flag leaf sheath and grain of YM49 was higher than that of other two cultivars, but the SPS activity in ear stem of LM1 was higher than that of other two cultivars. The SS activity in flag leaf, flag leaf sheath, ear stem and grain of YM49 was higher than that of other two cultivars,indicating the sucrose synthesis and degradation in the vegetative organs and grain of YM49 and LM1 were active. Correlation analysis showed that the starch and amylopectin accumulation in the grain of YM49 and LM 1 had strong feedback regulation to sucrose synthesis catalyzed by SPS. The SS activities in the grain of YM49 and LM1 were significantly(P0.01) correlated with the starch and amylopectin accumulating rate, but that of GC8901 was not. The results suggested that the SPS and SS activities in the vegetative organs and grain in three different wheat cultivars were closely related to starch accumulation.