Pleodorina japonica sp. nov. (Volvocales, Chlorophyta) with bacteria-like endosymbionts

Abstract

The morphology, reproduction and taxonomy of Pleodorina japonica Nozaki sp. nov. collected in Japan were studied using clonal cultures. This taxon is distinguished from the other species of Pleodorina and Eudorina by its unique vegetative colonies, in which only 20–27% of the cells are somatic and anterior, and in which the gelatinous matrix does not form individual sheaths. Zygote germination was observed for the first time in Pleodorina. A single biflagellate gone-cell moved out from the zygote wall. In addition, abundant bacteria-like endosymbionts in the cytoplasm of somatic and reproductive cells as well as in the male and female gametes and zygotes were revealed by means of 4'-6-diamidino-2-phenylindole (DAPI) staining and electron microscopy. The endosymbiont was rigidly rod-shaped, measured 1.5–1.9 μm long and emitted strong blue-white fluorescence under the epifluorescence microscope after DAPI staining, and it was surrounded by electron transparent areas. The generic delimitation between Pleodorina and Eudorina as well as taxonomy of species of Pleodorina are discussed, and four species of the genus Pleodorina, P. californica Shaw, P. sphaerica Iyengar, P. indica (Iyengar) Nozaki comb. nov. and P. japonica, are recognized.