Chlamydomonas ultrastructure and perspectives of green monads modern classification
Olga Boldina
Algol. Dept., Komarov Bot. Inst. RAS, St.Petersburg, Russia
Though polyphyletic origin of green monad genera has been proved by comparison of 18S ribosomal RNA gene sequences (Pröschold et al., 2001; Nakada et al., 2008) morphological criteria for complete substantiation of proposed clades are not yet presented. The ultrastructural survey of the strains that have been used for sequencing may be the first step towards improved classification. The analysis of more than 50 strains belonging to 30 species, described as taxons of Chlamydomonas genus, reveals the diverse ultrastructure organization of cell wall, nucleus, chloroplast thylakoids, stigma and pyrenoid, as well as mitochondria location. Different species demonstrates a specific set of ultrastructural characters, whereas different strains of the same species in every of 8 cases have almost identical cellular structure. Therefore, TEM observations support the existence of Chlamydomonas species, but not that of Chlamydomonas groups, suggested by Ettl (1976). During the comparison of the ultrastructural characters distributions in the phylogenetic trees a correlation between the species disposition on the tree and their pyrenoid structure has been detected. Moreover, the same peculiarities of pyrenoid structure have been found in other chlorophycean genera, having the closest to Chlamydomonas species disposition in the tree. But in some chlamydomonadacean species the visible pyrenoid has not been observed despite their close relation to Chlamydomonas. The noncasual distribution of ultrastructural characters in volvocalean "primary clades", designated by Nakada (2008), particularly in Moewusinia, Chloromonadinia and Reinhardtinia, has been found. Thus, our observations show that it is the set of ultrastructural characters that could contribute the base of modern phylogeny.
e-mail address of presenting author: