抄録
1. The life cycle of the green alga Chlorella was studied using the technique of “synchronous” culture. Successive stages of the life cycle were conveniently referred to as (i) growing phase, (ii) sporulating phase, and (iii) dividing phase. The growing phase represents the stage of transformation of “dark cells” into “light cells” according to the terminology of Tamiya et al. (l). The sporulating phase is the stage of ripening of light cells, and the dividing phase is the stage of formation of a number (n) of dark cells from individual light cells. Average values of n shown by the light cells of increasing grade of ripening were 1.3, 4.7, and 5.1, respectively.
2. The content (in percent of dry weight) of pentose-nucleic acid (PNA) was found, to be relatively constant throughout the whole course of cell transformation. In contrast, the percentage of desoxypentose-nucleic acid (DNA) decreased more or less in the growing phase, and increased markedly in the sporulating phase.
3. On incubating the cells in the dark, PNA content decreased, while DNA content increased especially markedly in light cells. The ratio of DNA increased to PNA decreased was found to be about 1:2-1:4. Based on these observations it was suggested that in the cell, DNA may be formed, at least partly, from PNA.
4. DNA content per cell of light cells after the incubation in the dark was found to be roughly proportional to the number of dark cells to be produced from individual light cells. This finding is in accord with the prevailing concept that DNA is contained in a constant amount in each nucleus.
5. In respect to total nitrogen and protein nitrogen, cells at various developmental stages showed almost the same content on a dry weight basis. Approximately constant were also the ratios: (PNA-P+DAN-P)/total-P, (PNA-P)/(PNA-P+DNA-P) and PNA-P/protein-N. It was further found that the ratios of PNA-P/(PNA-P+DNA-P) and protein/N/total-N coincided strikingly with each other.
This work was carried out as a part of the studies on the growth of Chlorella directed by Prof. Hiroshi Tamiya, to whom the writer is indebted for his guidance. Thanks are also due to Dr. E. Has e and Mr. Y. Morimura for their kind co-operation during the course of this research. This work was aided by grants from the Rockefeller Foundation and the Ministry of Education. To these bodies we extend our grateful thanks.
