Formation Of Rice Spikelet Number Per Panicle And Regulatory Mechanisms Of Nitrogen Top-Dressing

As the important food crop, the yield of rice has great effects to food security of our country. The spikelet number per panicle (SNP) is a component of rice yield, which affects the yield greatly, while the nitrogen top-dressing is a wild used application in crop production to increase rice yield, which has important regulation to SNP. So elucidating the formation of of SNP and the effect of nitrogen top-dressing is of importance for further understanding the mechanisms of the differences between various rice cultivars, the formation process of SNP, and the regulatory effect of nitrogen top-dressing, and for constituting cultivation measurement to getting higher yield. In the present study, diverse cultivars were used to investigate the genotypic differences of the components of SNP, the growth states of young panicle, the non-structural carbohydrate and nitrogen metabolisms of vegetative organs and the proteomic variation among the development stages of young panicle, furthermore, the root protein expression’s responses to nitrogen supplying status were analyzed to make a preliminary investigation to the physiological changes the nitrogen fertilizer triggered to the whole plant. The main results were summarized as follows:1. To investigating the components and the distributions of spikelet number per panicle, diverse cultivars were planted in pots with different top-dressing levels in five years. The results showed that, the spikelet numbers per panicle (SNP) and the components, such as the ratios of spikelet number on secondary branch (SNSB) to SNP, secondary branch numbers (SBN), the ratios of SBN to primary branch number (PBN), of Indica rice and inbred rice were higher than those of Japinica rice and hybrid rice, respectively; while the ratios of spikelet number on primary branch (SNPB) to SNP were performed conversely. The SNSB distributions on axis of Indica rice were more uniform than Japonica rice. The SBN was the SNP determinate factor of Indica rice, as for Japonica rice, both the PBN and SBN were the determinate factors. Nitrogen top-dressing application increased the SNPs, SNPBs, SNSBs, PBNs, SBNs and the ratios of SNSB to SNP, and decreased the ratios of SNPB to SNP of all varieties. The SBNs and SNSBs on the basal and middle side of axis were affected by nitrogen top-dressing more greatly than those on the top side of axis. The determinate affections of SBN to SNP were increased, and the increased levels of inbred rice and Indica rice were higher than those of hybrid rice and Japonica rice, respectively.2. Diverse cultivars were planted in pots with different top-dressing levels in five years, the panicle lengths and fresh weights were recorded each three days during panicle development stages and analyzed by growth dynamic method, the effects of nitrogen top-dressing and the relations between eigenvalues of growth curves with spikelet number per panicle and its components were discussed. The results showed that, the VmaxS of panicle length and fresh weight were significantly correlated with spikelet numbers per panicle (SNP); while the duration times from panicle initiation to the beginning time of fast growth stage (PI-t1) were not correlated with SNP. The vmaxs and the duration times from panicle initiation to the beginning time of fast growth stage of panicle fresh weight and panicle length of Indica rice and hybrid rice were higher than those of Japonica rice and inbred rice, respectively. Nitrogen top-dressing application prolonged the duration time from panicle initiation to the beginning time of fast growth stage and the vmaxs of panicle fresh weights and lengths of all cultivars used in this experiment.3. Wuyunjing 7 and 2401 were used to investigate the dry weight growthes, non-structural carbohydrate and nitrogen metabolisms of the four leaves, sheathes from top and the stem, and the regulatory effects of nitrogen top-dressing. The results showed that, the main differences of these cultivars were the characters of stem. All of the dry weight growth rate, NSC content and C/N ratio of 2401’s stem were increased during panicle development stage, while the stem dry weigth growth rate of Wuyunjing was slower, the NSC content and C/N ratio were decreased. Nitrogen top-dressing improved the dry weight and NSC accumulations of leaves and nitrogen contents of all organs tested, repressed the NSC accumulations and C/N ratios of sheathes and stem, these two cultivars had same performances.4. To analyze the variations of protein expressions during development and the effects of nitrogen-topdressing, the protein expression levels of young panicles at different development stage and under different levels of nitrogen-topdressing were studied by two-demension electrophisis and proteins were identified by mass spectrometry.64 proteins’ expression levels changed greatly during panicle development with 27 proteins affected greatly by nitrogen-topdressing.Among these 64 proteins,52 proteins were identified successfully, such as tasselseed-2, sucrose synthase, L-ascorbate peroxidase 1, and phenylalanine-lyase, etc; and these proteins had functions at the synthesis and signal transduction of phytohormones (four proteins), the metabolism of active-oxgen (two proteins), the development of floral organs and the regulation of fertility(11 proteins), the metabolism of carbohydrate and nitrogen (11 proteins), the formation of photosystem (eight proteins), the regulation of gene expression (six proteins), the degration of protein (four proteins), the metabolism of energy (three proteins), etc.5. A solution culture experiment involving three nitrogen treatments,0.14 mM NH4NO3 (low nitrogen (N)),1.07 mM NH4NO3 (normal N) and 2.14 mM NH4NO3 (high N) was conducted to investigate the proteomic response of rice root to N supply status. Proteins extracted from roots were profiled by two-dimensional gel electrophoresis, and differentially expressed proteins were analyzed by mass spectrometry. Seven protein spots, whose expression changed at both high N and low N levels, were successfully identified by mass spectrometry. According to the functions, these proteins were involved with the tricarboxylic acid cycle, energy metabolism, phenylpropanoid metabolism, and protein degradation.This thesis elucidates the underly mechanism of genotypic variations of SNP and the physiological effects of nitrogen top-dressing from componential, growth dynamic and dry material accumulation and partition angles, and uncovers the physiological mechanism of panicle development and the regulatory mechanism of nitrogen top-dressing from proteomic angle. All of these results lead a further understanding of the regulatory mechanism of nitrogen-topdressing to spikelet number per panicle, and provide new reference for making more reasonable measures to achieve higher yield in rice production.