Effects Of Nitrogen Treatments And Wx Protein Loss On Caryopsis Development In Rice

Rice is one of the most important crops in China, most of the cultivated rice are high-yield, while the rice qualities are not well. So improving the rice quality is more and more important for the demand of high-quality from people and rice trade. In rice caryopsis, endosperm is the mainly edible part, the development of endosperm is most important for the rice yield and quality. Many factors can influence the development of rice endosperm, such as heredity, climate, environment and cultivation, and one of the factor, the nitrogen fertilizer and its application time, are especially important to the yield and quality of rice. Many achievements have got from the research of nitrogen fertilizer on the rice yield and quality, but the effects of N-fertilizer on the development of rice caryopsis are rarely reported. In addition, the starch, especially the amylose in rice endosperm is correlative to cooking and taste quality. High amylase content in rice endosperm is bad for the rice viscosity, plasticity, polish and taste. The amylose is synthesized under the catalysis of granule-bound starch synthase (GBSS, Wx protein), so the quantity and activity of Wx protein in rice endosperm are important to the rice quality.In this research, the development of caryopsis was studied from intrinsic factor (Wx protein) and extrinsic factor (N-fertilizer). Firstly, the two rice cultivars, Yangdao No.6 and Jingdao 941, were used as materials, to study the effects of various nitrogen treatments on the development of caryopsis, accumulation of starch and endosperm microstructure. Secondly, the transgenic japonica and indica rice with antisense Wx gene were also used, to study the effects of the Wx protein loss on the development of caryopsis and accumulation of stored matter in rice. The main results were as follows:(1) The proper application of nitrogen fertilizer could increase the fresh and dry weight of the caryopsis, especially the N-fertilizer at the heading stage had significantly effects on the fresh and dry weight in caryopsis. Increased application of panicle N-fertilizer could remarkably increase the chlorophyll content in caryopsis and glume, butsignificantly decrease the soluble sugar in the developing rice caryopsis, and the starch content was slightly reduced. The nitrogen fertilizer at the heading stage was negatively correlated with the amylose content in caryopsis, and reduced the ratio of amylose to total starch in developing caryopsis, so the cooking and taste quality was greatly promoted.(2) During the development of rice caryopses, the activities of ADP-glucose pyrophosphorylase (ADPG-PPase), 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 initial stage of grain filling, and then depressed after reaching their peak at 10~15d after flowering. Application of nitrogen fertilizer could promote the activities of ADPG-PPase, SSS and SBE in developing grains at middle and late filling stage, and decreased GBSS activity in early and middle filling stage, and the effects of the N-fertilizer at the heading stage were higher than at the tilling stage.(3) The protein percent (%) in caryopsis decreased gradually during the rice grain filling, but the protein content in each grain (mg/grain) increased in the developing caryopsis. Increased the application of panicle N-fertilizer was significantly correlated with the protein content in caryopsis, and had evident effects on the development of protein bodies and amyloplasts. Moreover, panicle N-fertilizer could increase the filling of amyloplasts, decrease the ratio of chalk, so the apparent quality was greatly improved. In addition, the protein and fat content in aleurone layer were higher under N-fertilizer applictation, the aleurone grains became smaller and their number increased.(4) The amylose content in rice caryopsis was remarkably decreased with the loss of Wx protein. In transgenic rice with anitsense Wx gene...