Association of Potassium and Some Other Monovalent Cations with Occurrence of Polyphosphate Bodies in Chlorella pyrenoidosa

Abstract

Phosphate-starved Chlorella pyrenoidosa cells formed polyphosphate bodies (PB) upon transfer into nutrient solutions containing phosphate and potassium, or another monovalent cation, such as Na⁺, NH₄⁺, Li⁺, or Rb⁺. The phenomenon was studied by chemical analyses, light microscopy, and electron microscopy.

When the P-starved cells were transferred into a complete nutrient solution containing 100 micromolar P, they accumulated large quantities of P and K within several hours. The accumulation was accompanied by a corresponding appearance of PB in the cells. The absence of K from the medium prevented appreciable P accumulation and PB formation, but omitting Ca or Mg did not.

The P-starved cells exposed to a simple solution of at least 20 micromolar H₃PO₄ and 100 micromolar KHCO₃ responded in a similar manner as the cells exposed to the complete nutrient solution. However, the PB appeared structurally different.

It is proposed that monovalent cations are essential for PB formation in C. pyrenoidosa. K is suggested to be a major component of PB formed in K-sufficient media.

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