Changes in the content and distribution of the nucleic acid bases in Chlorella during the life cycle

Abstract

In the alga Chlorella ellipsoidea, using the technique of synchronous culture, changes in content and distribution of nitrogenous bases accompanying the life cycle were examined by fractionation of cell materials into acid-soluble, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) fractions. In the DNA fraction, marked changes are observed in the percentages of thymine and guanine, while those of adenine and cytosine remain constant. During active increase in cell mass, the RNA fraction contains more guanine, and less cytosine than is found in dark-incubated cells or during the period of vigorous DNA synthesis. Such changes may be most simply interpreted in terms of heterogeneity of both DNA and RNA in the cell. In the acid-soluble fraction, adenine and uracil are dominant. The percentage of adenine decreases at the time of vigorous DNA synthesis, while uracil shows a reverse trend; the percentages of guanine and cytosine remain constant during the life cycle. The purine to pyrimidine ratio increases during cell mass increase and decreases during vigorous DNA synthesis. A remarkably constant ratio of bases between the acid-soluble and nucleic acid fractions is taken as evidence for some regulatory pattern.