Abstract:

The amylose content of wheat grain is significantly correlated with amount of Waxy protein subunit. However, there is a great difference in amylose content among different wheat cultivars which all have three Waxy genes. In order to investigate the activity changes of enzymes involved in starch biosynthesis, the characteristics of starch accumulation in grains, and the relationship between them, two wheat (Triticum aestivum L.) cultivars, JM20 (lower amylose content in grains) and LM21 (higher amylose content in grains) were used in the study, which both carry three Waxy protein subunits. The results indicated that the activities of sucrose synthase (SS), adenosine diphosphorate glucose pyrophrylase (AGPP), soluble starch synthase (SSS), granule-bound starch synthase (GBSS) changed in the pattern of a single-peak curve during grain filling. The activities of SS, AGPP, GBSS, SSS and SBE in LM21, which had higher starch content, were higher than those in JM20. The accumulation rate of amylopectin was significantly or highly significantly correlated with the activities of SS, AGPP, SSS and SBE, and the accumulation rate of amylose was highly significantly correlated with the activities of SS, AGPP and GBSS. The accumulation courses of both amylopectin and amylose were well fitted to the logistic equation by relating amylopectin and amylose contents against days post anthesis. The simulation parameters revealed that the higher contents of amylopectin and amylose resulted from earlier initiating accumulation time and greater accumulation rate, but accumulation duration probably played a less important role for them. The amylose content in grains was mainly determined by GBSS activity as well as the activities of SS and AGPP. The change of GBSS activity reflected expression level of waxy gene was closely associated with the accumulation rate of amylose, indicating that amylose content in grains was determined by GBSS activity, especially at late grain filling stage. The difference in expression of waxy gene might be a major reason for the large difference in amylose contents between JM20 and LM21.

Key words: Winter wheat (Triticum aestivum L.), Grain, Amylose, Amylopectin, Enzyme activity