| The unsynchronized grain filling in hybrid rice with big panicle has negative effect on full grain percentage. Field tests and pot cultivation experiments were undertaken using a pioneer cultivar of "super hybrid rice", Peiai 64s/E32, and other cultivars as experimental materials. Systematic study was done on the phenomenon of unsynchronized grain filling in rice using 32P tracer technique, microstructure and ultrastructure observation, Endogenous hormone detection and exogenous hormone treatment, etc. The main results are as follows:1. Analysis on the yield components of Peiai 64s/E32 indicated that spikelets per panicle showed very high heterosis (48.16%) while heterosis of other components such as 1000-grain weight, seed setting percentage and ears per plant were not prominent. In the population of a cultivar, 6 characters (grain weight per plant, ear length, seed density of panicle, spikelets per panicle, grains of primary rachis branches and grains of secondary rachis branches) were positively correlated with each other and all the correlation coefficients were significant at 0.01 levels with correlation coefficients ranging from 0.590to 0.994, while the correlations between these 6 characters and seed setting percentage was insignificant.2. The seed setting density index (SSDI) was proposed and used to analyze the seed density of the panicle and the rachis branches. The SSDI of panicle in Pei-ai64s/E32 was 7.40, while the SSDI of rachis branches ranged from 1.20 at the top to 1.52 at the bottom of panicles.3. Richards equation W=A(l+Be-kt)-1/N was applied to simulating grain filling process of different types of spikelets. The pattern of grain weight increasing lines and parameters of superior and inferior spikelets showed wide difference, while those inferior spikelets after superior spikelets were removed narrowed its difference to superior spikelets in Peiai64s/E32.4.32P tracer experiment indicated that 32P was concentrated in seeds, both their radioactivity and specific activity are highest, about 1.5 ~ 5 times higher than that of vegetative organs in different cultivars. Radioactivity of seeds accounted more than 70%~80% of the total in different cultivars. The degree of P concentration in seeds represented roughly the efficiency of nutrients transportation from stem and sheath into seed.5.The grain filling of superior spikelets was a continuous progressing process without interruption: Free nucleus-endosperm cell formation-endosperm cells differentiating into aleurone layer and starchy endosperm-composition and storage of reserve materials such as starch and storage proteins. The process was normally completed within 20 d without much difference among individual superior spikelets.6. The second day after anthesis was a critic time for the grain filling of inferior spikeletsat free nucleus stage: The free nuclei either continued their development course to multiply and to form endosperm cells, or they stopped their development course and became aggregated, awaiting the favorable condition to resume its development process. The length of the stagnation varied greatly in different inferior spikelets.7. Ultrastructure of free nuclei in superior spikelets was characterized with "coral-shaped" nuclear matrix and clearly visible nucleoli, while nucleoli disappeared in the evenly aggregated free nuclei of some inferior spikelets. The rapid degeneration of dorsal and abdominal nucellus occurred along with the rapid multiplication of free nuclei in superior spikelets, while the nucellus remained intact during stagnation periods in inferior spikelets till resuming their endosperm development.8. Grain filling rate was positively correlated with endogenous IAA, ABA and GA1+GA3 with the highest correlations between IAA content per unit fresh weight (ng/g FW) and fresh weight increase rate (r=0.8218**) and between the average IAA content per grain (ng/grain) and dry weight increase rate (r=0.8485**). Path analysis of restricted model indicated that endogenous IAA, ABA and GA1+GA...
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