Accumulation of Proteins in Giant Cells, Induced by High Boron Concentrations in Chlorella pyrenoidosa

Abstract

Cell division was altered when the cells of Chlorella pyrenoidosa were exposed to boron concentrations ranging between 50 and 100 mgl −1 . Nuclear division was normally achieved, as electron micrographs and DNA contents showed, but cytokinesis was delayed for 72 h. During this time photosynthesis was only 50 % inhibited. In this manner the formation of daughter cells was more severely inhibited than the synthesis of biomass, leading to the formation of giant cells. These giant cells attained a high protein content which resulted from an increase in the nitrate uptake. As expected by the increase in protein content, total amino acids were increased in the giants cells. This enhancement affected not only protein amino acids but also non-protein amino acids principally ornithine and citrulline. On the other hand, chloroplasts showed a drastic alteration, due to an accumulation of a dense material, probably proteins, which appeared surrounded by thylakoids.