Influence of anomalous environmental conditions upon einbryogenesis in the rice plant, Oryza sativa L. : I. Histochemical observation of norinal embryogenesis.

Abstract

1. As a fundainental investigation for the study of genetical effect of zinoma.lous envirdnmerital c. onditians upon rice embryo during its development the process of normal embryogenesis has been observed histochemically as well as morphologically. Nprin No. 17, an improved paddy variety, was used here as the materialsL 2. The zygote underg:oes cleavage during" the first 3 days after fertilization. It increases abruptly its cells during the period betweeh the 3rd and the 4th day, the.number of cells counted on the 4th day being ca. 15 times as many, as that on the 3rd day. From the 5th to the 8th day the young embryo multiplies its cells rather slowly, the avetage rate, of multiplication beihg ca. 150%. It shows again a rapid cell inbrease between the 8 thL and the 9th day (ca. 300%) Frorh this time on the rate of cell tnultiplication of einbryo ss a wholebecomes lower and lower as the development p.ro ceeds. The former abrupt cell increase is carried out before any sign of cell differehtiation has been recognized both morphologically and histochemically. Th.e latter is confirmed to be due to the speedy division of ceils forming the scutellurh and theseed, Iing organs including the coleoptile, the coleorhiza, the radicule and the primordial first foliage leaf. These have, then differentiated 'already alongr with the.epithellium. In the tissue f:orming the seedling organs cell multiplidation goes on actively until the Iatter stages. The scutellum cells, however, show no active division after the 9 th day, because they have nearly come to their maximurn nurrLber already by this time. The epithellial cells continue their division rather actively throughout the develop, ment, but they are aiw-ays the least in number and contribute little to the total gain (Table 1 and Figure 1).