692 



Shigetoh Miyachi 



fraction showed only a slight increase, confirming our previous conclu- 

 sion that most of P for the synthesis of P -lipid is supplied from the 

 external medium. 



Experiments in darkness - Using the cell material which cannot 

 synthesize RNA in the dark in P-free medium, it was found that no 

 change was observed in the amount of total P or P-'^ in the respective 

 cellular P-compounds except the gradual increase in poly-P "A". 

 From these results as well as those described above it may be concluded 

 that mobilization of P from an intracellular P compound to poly-P"A" is a 

 light -independent process while the transfer of P from polyphosphates to 

 other cellular P-compounds such as DNA and P-protein is a light depend- 

 ent process. 



Incorporation of phosphate under normal photos ynthe tic conditions or in 

 the dark 



Chlorella cells which had been growing in the "cold" normal medium 

 were supplied with P^^ -labeled phosphate under photosynthetic conditions 

 or in the dark, and the subsequent process of incorporation of P^^ by the 

 cells into poly-P"B", poly-P"C", labile nucleotides, lipid, DNA and pro- 

 tein was followed for comparatively short periods (0. 5-8 hours). It was 

 found that the synthesis of poly-P"C" occurs only in the light whereas 

 that of poly-P"B" and P-lipid takes place independent of light at least for 

 a limited period. 



DISCUSSION 



This study has revealed that under normal photosynthetic conditions, 

 P for the syntheses of intracellular P-compounds such as DNA and P-pro- 

 tein is supplied from poly-P"C" and poly-P"A" whereas that for the syn- 

 theses of RNA and P-lipid is supplied from extracellular orthophosphate 

 without the intervention of polyphosphates. Most of poly-P"B" and poly-P 

 "D" are not normally mobilized. Under P-deficiency in the light, how- 

 ever, synthesis of not only DNA and P-protein but also RNA is maintained 

 with concomitant decrease of all kinds of polyphosphates. These observa- 

 tions indicate that poly-P"B" and poly-P"D" are P-reservoirs which are 

 used only under P-deficiency. It is assumed these polyphosphates are 

 degraded to orthophosphate before transfer to other cellular P-compounds. 



One might assume that the acid -insoluble nucleotidic labile P is a 

 hydrolysis product(s) of stable RNA -nucleotides. But the facts that 



^ 



