691 



Shigetoh Miyachi 



observed(^). In most cases poly-P"A" showed a tendency to increase in 



darkness. 



Changes in contents of total P and P^^ occurring on incubating P^^ -labeled 

 Chlorella in normal "cold" medium 



Experiment in light - The uniformly P^^-i^^jjeie^j cells were trans- 

 ferred to the "cold" standard medium, and the changes of distribution of 

 P-^^ as well as of total P in various fractions were followed. In the pre- 

 vious experiment(^) it was shown that the course of increase of total P in 

 the DNA -fraction and in the protein -fraction almost exactly coincided 

 with that of P^^, indicating that phosphorus for the synthesis of DNA and 

 P -protein is supplied from the intracellular P -source. As in the P-free 

 experiment, RNA-P, poly-P"D" and acid insoluble nucleotidic labile P 

 were not separated in this experiment but only the total P of these com- 

 pounds ("total RNA-fraction") were assayed. Data for the above three 

 compounds are reproduced in Fig. 3, and are in accord with the previous 

 observation that phosphorus in the "total RNA-fraction" is supplied 

 almost exclusively from the surrounding solution. It was further shown 

 in this figure that RNA-P-^^ increased only slowly whereas RNA -total P, 

 as calculated from the UV -absorption, increased steeply, and confirmed 

 our previous conclusion that during photosynthesis the phosphorus used 

 for most of the RNA taken from, the extracellular P source, although some 

 RNA is supplied through intracellular phosphorus. P^^ in poly-P"D" and 

 nucleotidic labile P did not decrease or decreased only slightly although 

 they took up phosphorus from the surrounding medium. In Fig, 4 are 

 shown results demonstrating the changes in total P and P^^ in other poly- 

 phosphates. (For technical reasons (because of the addition of carrier 

 polyphosphate in the assaying procedure) the total P content in poly-P"A" 

 cound not be determined. ) As may be seen in the figure, P^^ in poly- 

 P"A" and poly-P"C" always decreased steeply, whereas P^^ in poly-P"B" 

 decreased only slowly or did not decrease in some cases. From these 

 results it may be assumed that only poly-P"A" and poly-P"C" are func- 

 tioning in the mobilization of P to other intracellular P-compounds such 

 as DNA and P -protein under normal photosynthetic conditions, Poly-P 

 "B" and poly-P"D" are functioning as P-reservoirs wliich are used only 

 under conditions of P-deficiency, 



It was also observed that the decrease in poly-P-^'^ "A" is usually 

 preceded by a transient increase. It may be inferred from this finding 

 that poIy-P"A" accepts and transfers P from and to other intracellular 

 P-sources. Although it was not shown in the figure, P^^ in the lipid 



