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The effect of glucose and 2-thiobarbituric acid on the biosynthesis of cell constituents such as protein, carbohydrate, DNA, RNA, phospholipid and PCA-soluble phosphate compounds in Chlorella during the life cycle was measured, and the changes in the content of these main cellular components of the algal cell were analyzed in connection with the nuclear and cytoplasmic division. In the normal autotrophic synchronous culture the contents of protein, RNA, and DNA in the cell showed a chracteristic changes according to the progress of cell development, increasing more or less throughout all the life cycle. The synthesis of protein is more prominent in the division period and that of DNA is more active in the ripening period, while the synthesis of RNA is more rapid in the growing and ripening periods than other developmental stages. The period of division cycle was little affected by glucose in the medium, although the synchrony of the growth and cellular division was disturbed and the n value increased. The cotents of protein, carbohydrate, RNA and DNA of the cell were increased by the glucose treatment throughout all the life cycle. On the other hand, both of cellular growth and division were retarded severely and the n value was decreased by the 2-thiobarbituric acid treatment throughout all the life cycle. On the other hand, both of cellular growth and division were retarded severely and the n value was decreased by the 2-thiobarbituric acid treatment. The synthesis of protein, carbohydrate, DNA, RNA and phospholipid of the cell was also retarded by 2-thiobarbituric acid. In the autotrophic, mixotrophic and 2-thiobarbituric acid-treated cultures, each having different mode cytoplasmic division, a common general schema occurring in the cell during the life cycle may be drawn as follows. The ratio of RNA to protein attains maximum value in the L₁-cell stage prior to the nuclear division and thereafter decreases during the periods of ripening and division. The ratio of PCA-soluble phosphate compounds to protein increased from the begining of the culture to L₄-cell stage successively and thereafter decreased gradually during the division period, while the ratio of protein to DNA kept almost constant up to the division period and thereafter increased during the division period. Therefore, it is presumed that the increase in the ratio of RNA to protein is to be an inducer of nuclear division and that the cytoplasmic division is induced by the increase in the ratio of protein to DNA.
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