Intracellular Structure of the Unicellular Red Alga <i>Cyanidioschyzon merolae</i> in Response to Phosphate Depletion and Resupplementation

Abstract

SummaryIn algae, vacuolar polyphosphate stores phosphate, regulates osmotic pressure and cytosolic pH, and buffers metallic cations. However, its metabolism is not well understood. Cyanidioschyzon merolae cells contain four to five vacuoles storing polyphosphate whose degradation and synthesis are induced by phosphate deprivation and resupplementation, respectively. To understand polyphosphate metabolism, we observed C. merolae cells cultured in different phosphate conditions by electron microscopy. In the phosphate-containing medium, the vacuoles contained electron-dense substances presumably consisting of polyphosphate and metallic cations. When phosphate was depleted, the vacuoles lost the electron-dense substances, and lipid bodies in close contact with vacuoles and starch grains appeared in the cytoplasm. When phosphate was added again, small, electrondense granules or vesicles appeared in the cytoplasm. Some of them were in contact with the vacuoles and had been taken into the vacuolar lumen, suggesting the possibility that polyphosphate is synthesized and transported to the vacuoles in these structures.

Modeling With Uncertainty Quantification Identifies Essential Features of a Non-Canonical Algal Carbon-Concentrating Mechanism

“…The model geometry is based on the cellular structure of C. merolae as apparent in published micrographs of this alga (22)(23)(24)(25)(26)(27)(28)(29)(30)(31). The modeled cell and its boundary layer form a series of concentric spherical well-mixed compartments.…”