EFFECTS OF CO2 CONCENTRATION DURING GROWTH ON THE INTRACELLULAR STRUCTURE OF CHLORELLA AND SCENEDESMUS (CHLOROPHYTA)1

Abstract

ABSTRACT Effects of CO2 concentration during growth on intracellular structure were studied with ftve species of Chlorella and Scenedesmus obliquus. Cells grown under ordinary air conditions (low‐CO2 cells) had a well developed pyrenoid surrounded by starch, while those grown under high CO2 conditions (high‐CO2 cells) had a less developed pyrenoid or no detectable pyrenoid. Two mitochondria, one at each side of the neck of the projection of the chloroplast close to the pyrenoid, were found in low CO2 cells of C. vulgaris 11h. Usually, lamellar stacks extended in parallel in the chloroplast of low‐CO2 cells of C. vulgaris 11h, while a grana‐like structure was found in high‐CO2 cells. However, in C. pyrenoidosa, grana like structures were found more commonly in low‐CO2 cells than in high‐CO2 cells. These results suggest that development of pyrenoid starch is generally correlated with growth under low CO2 conditions, whereas CO2‐effects on lamellar stacking are species dependent.