Comparison of Caryopsis Development Between Two Rice Varieties with Remarkable Difference in Grain Weights

Abstract: Two rice (Oryza sativa L.) varieties, Ootikara with big grain (36 mg/grain) and Habataki with small grain (18 mg/grain), were used to study the factors that control caryopsis development. We compared the differences of caryopsis weight, the number of endosperm cell, the structures of pericarp and endosperms, changes of physiological activities, and so forth during the caryopsis development. The main results showed that the growth period of the cell of ovary wall and the caryopsis of Ootikawa was longer compared with that of Habataki, resulting in the formation of more endosperm cells and heavier cell weight. In Ootikawa, it has a longer period of maintaining a high level of dehydrogenase and catalase activities, and higher level of respiratory rate of the ears, the degree of greening and photosynthetic rate of the flag leaf, and a longer functional maintenance period of the dorsal carpellary bundles in the ovary. And all these features indicated that the larger capacity and the longer active period of the caryopsis in Ootikara would lead to the notable expansion of the caryopsis. Key words: rice; caryopsis; endosperm; amyloplast; aleurone layer In rice, the dry weight of the endosperm accounts for more than 90 per cent of the caryopsis and its developing determines the weight and quality of rice grains. Many in-