Abstract
Endogenous dark respiration in the blue-green alga Plectonema boryanum is markedly affected by preincubation in the light: it can be increased from a basal rate of 5 nmoles of O(2) to 55 nmoles of O(2) per mg of cell protein per min after exposure of the cells to light for 8 to 10 hr. Under conditions of enhanced dark respiration, cyanophage multiplication in the dark increases drastically and approaches the cyanophage yields obtained in photosynthesizing Plectonema cells. This implies that the biosynthetic capabilities of the algal cells, at least with respect to viral synthesis, can be similar in the dark to those in the light. The enhanced endogenous respiration rate was found to be dependent on photoassimilation of CO(2) and on protein synthesis. The implications of these findings with respect to obligate photoautotrophic metabolism in blue-green algae are discussed.