Effect Of The Activities Of Key Enzymes Involved In Starch Biosynthesis On The Structure Of Starch In Developing Rice Endosperm

The dynamic changes of the activities of enzymes involved in starch biosynthesis, including ADP-glucose pyrophosphorylase (EC.2.7.7.2 1), starch synthases (EC.2.4.1.21), starch branching enzyme (EC.2.4.1.18) and starch debranching enzymes (EC.3.2.1.41) were studied during grain development, using rice varieties with different ratios of amylose and amylopectin. Changes in structure of amylopectin were characterized by isoamylase treatment, followed by Sephadex G75 Gel-chromatography. The relationships between the activities and the formation of starch structure during the development of rice endosperm were also analysized.The results indicated that: The activities of enzymes are differentially expressed during rice endosperm development. Soluble starch synthase is relatively highly expressed in young endosperm whilst maximal later stage of endosperm development, implying that the contribution of each enzyme to starch biosynthesis changes during endosperm development. Qualitative measurement of amylopectin structure from developing endosperms confirms that the nature of amylopectin structure changes during 6 rice endosperni development and that this correlates with the differential expression of enzymes.