Comparative study of chloroplast morphology and ontogeny in Asterochloris (Trebouxiophyceae, Chlorophyta)

Abstract

Confocal laser scanning microscopy was utilized to compare the chloroplast morphology and ontogeny among five strains of the green alga Asterochloris. Parsimony analysis inferred from the rDNA ITS sequences confirmed their placement in three distinct lineages: Asterochloris phycobiontica, Trebouxia pyriformis and Asterochloris sp. Examination by confocal microscopy revealed the existence of interspecific differences in the chloroplast ontogeny of Asterochloris; this was based upon either specific chloroplast structures observed in a single species, or on the differential timing of particular ontogenetic sequences. The occurrence of flat parietal chloroplasts prior to cell division, considered as a basic morphological discriminative character of Asterochloris, was clearly associated with the process of aplanosporogenesis. By contrast, chloroplast transformation prior to the formation of autospores proceeded simply by the multiple fission of the chloroplast matrix in the cell lumen.