Starch Synthesis in Chlorella Vulgaris

Chlorella vulgaris was found to deposit starch, in amounts up to 20% of the dry weight of the cells, when grown in a medium containing glucose. The cells did not contain cellulose or chitin. The starch was difficult to extract, being associated with an alkali-soluble, dextrorotatory, cell-wall polysaccharide. The starch, after extraction by a 26% solution of calcium chloride at 120 °C., had properties quite similar to starches from higher plants. It was composed of amylose (30–40%) and amylopectin. Glucose-1-C14 was incorporated into the starch, by growing cells, without much breakdown and resynthesis. Cell-free extracts, obtained from the alga, contained a phosphorylase and a branching enzyme similar to those of the potato. These brought about the synthesis of an amylopectin–glycogen type polysaccharide from glucose-1-phosphate. It is concluded that the mechanism of starch synthesis in Chlorella vulgaris is essentially the same as in higher plants.