Abstract
Grain size and shape are important traits in rice. However, it is not yet been fully understood how the grain size or shape is determined during plant development. In the present study, we analyzed the growth of rice grain in detail, using five cultivated strains (O. sativa) and one wide strain (O. rufipogon=perennis). The growth of rice grain was characterized by the initiation of rapid growth immediately after flowering and the abrupt cessation of the growth at maturing stage, suggesting a non-logistic growth. Also, relative growth rates in length and width and the allometric growth between length and width showed a non-logistic nature of growth. The final grain length correlated well with the maximal growth rate in length. But the final grain width was closely related to the growth period, not to the maximal growth rate. This shows that the grain size is controlled by different parameters, depending on the direction of the growth. In the cultivated strains, the minimal ratio of grain width to length, which was attained on the second to fourth day after flowering, correlated with the final ratio. Therefore, a final grain shape can be estimated by the minimal ratio. These results show that rice grain has a non-logistic and unique mode of growth not observed in the growth of glume or embryo.
