Effects Of Various Nitrogen Treatments On Caryopses Development,Endosperm Microstructure And Ripening Grains Qualities

Pot experiments were conducted to study the effects of various nitrogen treatments on rice seedlings' growth, caryopses development, endosperm microstructure and ripening grains qualities by two commonly grown rice cultivars. The main results are the following:(1) The increased nitrogen fertilizer used at the tillering stage can significantly enhance the fresh and dry weights, tillering numbers and heights of rice seedlings. The same is true for the chlorophyll and soluble protein content in the rice flag leaf when topdressing was used at the heading stage, it can retard grain filling process and senescence in the later stage of rice.(2) The topdressing ratio of nitrogen fertilizer at the heading stage is positively correlated to the chlorophyll content in caryopses. The nitrogen fertilizer treatments had significantly effect on the fresh and dry weights of the caryopses. Increased of application rate of ear manture can decrease significantly soluble sugar at the initial stages of the rice grain fillling and starch content in caryopses.(3) The amylose and amlyospetcin content in the caryopses increase gradually with the increased weight of grains, and the accumulation of them were simultaneity at the same time. Topdressing ratio of nitrogen fertilizer at the heading stage is negatively correlated with the amylose content in caryopses, and topdressing ratio of nitrogen fertilizer at the heading stage affected the ratio of amylose to total starch in caryopses development.(4) The changes of ADPG-PPase(AGP), soluble starch synthase(SSS), granule-bound starch synthase (GBSS) and starch branching enzyme (SBE) activities in the caryopses is a single peak curve. That is, the enzyme activities increase at the initial stage of grain filling with day after flowering, reach their peak at 10~15d after flowering, and then activities of them decreased with days increase. Increased topdressing ratio of nitrogenfertilizer at the heading stage can enhance AGP, SSS and SBE enzyme activities in grains, and decrease GBSS enzyme activity in early filling.(5) The protein percent content in caryopses decreases gradually during the rice grain filling, but the protein content in each rice grain increases with the grain weight increasing. Increased of application rates of ear manture is markedly positively correlated with the protein content in caryopses. Increased topdressing of nitrogen fertilizer at the heading stage had significant effect on the development of protein bodies and amyloplasts, and the formation of aleurone layer in caryopses. It can retard grain filling process and make amyloplasts developed enough.(6) Increased topdressing of nitrogen fertilizer at the heading stage raised the ratios of brown, fine and integrated fine rice grains and increased protein content compared with the control group, while decreased the degree of opaqueness and amylose content. That is, the nitrogen fertilizer can markedly improve the rice grain qualities.