Occurrence of microbodies in the green algaBracteacoccus cinnabarinus grown heterotrophically

Abstract

A comparative study was made of the ultrastructure and abundance of microbodies in the green algaBracteacoccus cinnabarinus grown photoautotrophically and heterotrophically on a conventional culture medium containing sodium acetate, potassium acetate and glucose. Several changes were observed in the cells maintained under these conditions. Most noticeably, cells grown on acetate in both light and dark were packed with lipid bodies. Microbodies were found to be closely appressed to the lipid bodies in cells grown heterotrophically in the dark on sodium acetate and potassium acetate. The average number of microbody profiles per cell was in general threefold greater in cells grown on sodium acetate than those grown on potassium acetate. No microbodies were observed in cells maintained photoautotrophically on the three carbon sources or in cells maintained photoautotrophically on Bristol's inorganic medium alone. Cytochemical staining with 3,3′-diaminobenzidine indicated the presence of catalase in the microbodies. The presence of microbodies suggests that the organelle may be performing functions similar to glyoxysomes in higher plants, namely the net conversion to succinate of acetyl CoA derived from lipid degredation. It is also apparent thatBracteacoccus can grow well as a heterotroph in the dark when acetate is included in the culture medium as a source of carbon.