Effects of Nitrogen on Starch Accumulation and Activities of Enzymes Involved in Starch Synthesis in Rice Caryopsis

Abstract

Starch accumulation is the main event in the developing rice grain, and the activities of key enzymes involved in starch synthesis are the important factors affecting the grain filling. N-fertilizer can regulate the plant growth, flower emergence, grain yield and quality, while the effects of N-fertilizer on starch accumulation and the activities of key enzymes in rice grains are rarely known. In this study, two rice cultivars, Yangdao 6 and Jingdao 941, were used as materials to study the effects of nitrogen on starch accumulation and the activities of related enzymes involved in starch synthesis. The results indicated that increased panicle N-fertilizer could significantly decrease the soluble sugar in the developing caryopsis, while the starch content reduced slightly. The amylose and amylopectin contents in the caryopsis increased synchronously with the raising of grain weight. When the pani-cle N-fertilizer was added, the amylose content in caryopsis as well as the content ratio of amylose to total starch decreased ob-servably. During the development of rice caryopses, the activities of ADP-glucose pyrophosphorylase (AGP), granule-bound starch synthase (GBSS), soluble starch synthase (SSS), and starch branching enzyme (SBE) in endosperm changed as single peak curve. That was, the enzyme activities increased at the early stage of grain filling, till their peak at 10–15 d after flowering, then depressed. Application of nitrogen fertilizer could improve the activities of AGP, SSS, and SBE in rice caryopsis at middle and late filling stages, while decrease GBSS activity at early and middle filling stages. And the effect of the N fertilized at the booting stage was superior to that at the tilling stage.