Developmental Differences among Different Positions Grains in Japonica Rice with Erect Panicle Type

Researches showed that the insufficient of nutrition supply was one reason for poor development of endosperm in rice,however, how much does this suppression effect has, was not very clear. So, a EPT-rice with large-spike cultivar was selected as material to compare the development of endosperm between the grains of first and second branches using gradient reducing sink treatment. A Logistic equations was used to simulate endosperm cell proliferation of grains on different parts of rice panicle,for researching the correlation between grain weight and the number of endosperm cell. The results showed: The number of endosperm cells at superior grain of upper parts of a panicle improved with the increasing of source-sink ratio after the treatment of reducing sink. It could achieve the optimal level under natural conditions. However, those cell numbers of inferior grain at lower parts of a panicle were poorer than all of the superior grain, especially lower than superior grain of upper parts of a panicle. Logistic fitting parameters showed that the initial cell proliferation potential(R0) was the upper the middle lower and the superior grain inferior grain. Effective proliferation period of endosperm cell(D) showed the upper the middle the lower, and the superior grain inferior grain. After the treatment of reducing sink, the R0 dropped and the D increased. The difference of grain weight between superior grains and inferior grains of the same position was not significantly reduced with increasing the source-sink ratio. The sink-source relationship is not the main factor limiting inferior grains development.Significantly positive correlation existed between the endosperm cell number of one grain and single grain weight(SGW). The significant correlation also existed among SGW, R0 and the durations of cell proliferation. These results suggest that the difference of the SGW between upper superior grains and lower inferior grains was because of the slower endosperm cell proliferation and the less number of cells. The grain weight would significant increased by reducing sink and increasing source, and the inferior grain growth was still not up to the level of superior grains. The results showed that inferior grains itself sink activity was the main factor restricted its development.