Phosphate metabolism in blue-green algae. I. Fine structure of the "polyphosphate overplus" phenomenon in Plectonema boryanum

Abstract

Changes in cell architecture at the electron microscope level have been followed in P. boryanum during conditions of phosphate starvation and rapid uptake. Cells from 14-day-old cultures were starved of phosphorus for 5 days and then inoculated into a medium containing 10 mg PO₄/liter. Polyphosphate bodies developed in five different areas of the cells: (1) in ribosomal areas, (2) on strands of DNA, (3) intrathylakoidally, (4) in polyhedral bodies, and (5) in areas of medium electron density which develop in nucleoplasmic areas. In control cells types 1 and 2 predominate. In phosphate-starved cells types 1, 2, and 5 predominate, and under conditions of rapid uptake types 4 and 5 are predominant. Details of the development process and its significance are discussed. In addition to the described variations in polyphosphate bodies during phosphorus starvation, the number of cyanophycean granules and lipid-like inclusions increase. Cell division is also abnormal in many of the phosphorus-starved cells, with both small cells and abnormally large cells being common. Thylakoid structure is altered under different phosphate concentrations. Expanded thylakoids are found in control algae; the frequency increases during starvation with the greatest number occurring during a rapid uptake. Other aspects of cell architecture are discussed in relation to the "overplus phenomenon."