Morphological transformations and lipid synthesis in chloroplasts of dark-treated Acetabularia mediterranea (lamouroux)

Abstract

The chloroplasts of Acetabularia mediterranea cells exposed to darkness possess thylacoids that become shorter that usual and disposed in stacks of numerous membranes. These transformations occur in about 2 weeks at all levels of the cell. In darkness the lipid content, especially galactolipids and monounsaturated fatty acids, decreases for two weeks and then remains stable. When the cells are returned to the light all the short thylacoids rearrange themselves but this rearrangement shows the usual apicobasal gradient observed for most of the metabolic activities in Acetabularia. Moreover the synthesis of metabolically active lipids, fatty acids, galactolipids and phospholipids (PL) starts again. These findings seem to indicate that the plastid modifications that occur in the dark are probably not linked to active membrane biosynthetic processes.