Night synthesis of protein by algae1

Abstract

Dunaliella tertiolecta in culture showed rates of net protein synthesis at night nearly equal to those during the day. In night protein synthesis carbon stored in carbohydrates and metabolite pools was used, whereas sulfate was assimilated from the medium as needed. As a result, whole cell C:S ratios varied systematically over the diel cycle, while the C:S ratio of isolated protein remained constant. In the stationary phase, sulfate incorporation into protein, unlike carbon incorporation, measured net protein synthesis rather than turnover. Diel experiments with natural populations of marine and freshwater algae demonstrated that night protein synthesis is a general phenomenon in phytoplankton. For samples previously exposed to saturating light, day and night rates of protein synthesis were similar. The use of carbohydrate and metabolic pool carbon for night protein synthesis not only increased protein to the food web, but also altered ratios of protein, carbohydrate, and lipid to one another. The latter might result in changes in the nutritional value of phytoplankton to herbivores.