The novel light-harvesting pigment-protein complex of Mantoniella squamata (Chlorophyta): Phylogenetic implications.

A light-harvesting pigment-protein complex has been isolated from Mantoniella squamata (Micromonadophyceae, Chlorophyta) by nondenaturing polyacrylamide-gel electrophoresis. The complex runs as two bands of molecular weights 54,000 and 55,000. There are two constituent polypeptides of molecular weights 20,500 and 22,000. Antibodies were raised to the 20,500-dalton polypeptides from this complex and to the 24,500-dalton polypeptide from the analogous complex of Pedinomonas minor (Micromonadophyceae). The antibodies to the M. squamata polypeptide are specific for both polypeptides of the M. squamata light-harvesting complex, as well as for a 27,000-dalton polypeptide of undetermined function. The antibodies to the P. minor polypeptide are specific for polypeptide components of the light-harvesting complex of that alga. The antibodies specific for the M. squamata light-harvesting complex polypeptides do not cross react with any polypeptides of P. minor thylakoid membranes, as demonstrated by crossed immunoelectrophoresis. Similarly, no polypeptides of M. squamata thylakoids cross react with the antibodies specific for P. minor light-harvesting complex polypeptides. These results indicate that the light-harvesting complex of M. squamata is structurally very different from that of P. minor. In a survey of several land plants and green algae, including representatives of all classes of green algae, a light-harvesting complex homologous to that of M. squamata was found only in Micromonas pusilla. All other organisms tested possessed a lightharvesting complex homologous to that of P. minor. The evolutionary and taxonomic implications of the novel M. squamata light-harvesting complex are discussed. [ABSTRACT FROM AUTHOR]