Studies on the Developmental Physiology of the Endosperm Tissue in Rice Plants : 1. Cytological heterogeneity in endosperm tissue

Abstract

In order to clarify the heterogeneity of endosperm tissue, which is seemed to be mainly caused by 3n, the pattern of cell division and the behavior of endosperm nuclei accompanying with early development of rice endosperm tissue were investigated. Mitosis was generally observed in the endosperm, but particularly it was not succeeded by cytogenesis in free nuclear stage. The abnormal figures frequently observed in the processes of cell division indicated heteropycnosis of chromonema (plate 7), chromosome clump (plate 8-10), laggard chromosome (plate 11, 12), retard of phragmoplast formation (plate 14, 15), multinucleate cell (plate 21-25), multipolar division (plate 16-19), amitosis (plate 26), and karyogamy or migration of nucleus (plate 20). The frequency of abnormal division for total number of mitotic cells was about 10%. While the frequency of multinucleate cell for total number of observed cells was about 0.3%. The cell size and the variation in diameter increased with development of endosperm tissue. The increment in nuclear size and the variation in diameter showed the same tendency as the cells did. But the nuclei decreased their length in the minor axis and finally indicated ellipsoid shape. The variation in nuclear volume increased with the development of endosperm tissue. This variation markedly increased with 6 days of age after flowering. The frequency of multinucleate cell also increased with the development of endosperm tissue and this increment were remarkable after the inception of starch grains. From these results it was confirmed that the nature of the endosperm tissue in rice plants is heterogenous.