Studies on the Development of Endosperm in Rice : 3. Observations on the cell division.

Abstract

Extending over the 6th to 8th day after anthesis, ripening rice caryopses were collected every two hours. Samples thus collected were fixed with FAA, and then cross sections obtained from the middle portion of the endosperm were stained with Delafield's Haematoxylin. Cell division occurred mainly in the early morning (from 2 a. m. to 8 a. m., accounting for 50-72% of the all samples), and after passing through the rest stage in the day-time (from 10a. m. to 4 p. m. ), it reoccurred in the evening. It was observed that from evening to midnight, the time for cell division and resting stage were repeated alternately (Tables 1 and 2). The periodicity of cell division had connection with the day-night rhythm, while it was thought that the pattern of the division cycles might differ according to age of the tissue. Average time required per cell division was 45-55 minutes. Resting time in early morning was very short, while that in the day-time was very long. It became evident that the section of the cell division was not confined to the outermost cell layer of the endosperm. Namely, 86% of the total cell division was observed in the outermost cell layer of the tissue, and 14% in the 2nd and interior cell layers. Basing on the observations, the process of the tissue formation shown in the Report 1 on this investigation has come to be revised, because in the case of Report 1, the tissue formation process had been deduced from the hypothesis that the cell division occurred only on the outermost layer. In the case of division of the cells found in the interior portion of tissue, the features have been found in that the cells were divided into two caused by the nuclear division which occurred after the enlargement of size of cells has reached twice as large as the surrounding ones.