Difference in caryopsis development among four rice varieties differing in grain weight.

Caryopsis development was investigated with four rice varieties as materials which differed remarkably in grain weight.The number of endosperm cells was calculated by the technique that the endosperm cell suspension was filtered with a microspore filtering membrane.The structure of pericarp and endosperm cells was observed with a light microscope and an electron microscope.For the large-grain varieties,the caryopsis development was slower,the number and dry weight of endosperm cells,weight of each endosperm cell were more than those in the small-grain ones.With the same grain weight,the caryopsis development and starch accumulation in indica rice were faster than those in japonica rice.In the large-grain varieties,the starch accumulation and cell growth yield in ovary wall cells were more than those in the small-grain ones.Also the pericarp and the dorsal vascular bundles in the ovary maintained a longer functional period.The outer layer endosperm cells transformed into aleurone layer cells 7 days after flowering in the small grain varieties,but 10 days after flowering in the large-grain ones.The larger space formed by both the inner and outer glumes and longer active period of the caryopsis in the large-grain resulted in the notable expansion of the caryopsis.