SEXUAL PROCESS IN SEVERAL HETEROGAMOUS CHLAMYDOMONAS STRAINS IN THE SUBGENUS PLEIOCHLORIS

A soil sample from the Zimbabwe region of Rhodesia yielded a number of clones of Chlamydomonas. All the clonal isolates belong to the subgenus Pleiochloris, they exhibit homothallic and heterogamous sexual reproduction, but they differ in their zygote wall ornamentation. Male gametes are differentiated by successive cleavage of the protoplast to form naked biflagellated sperm. Female gametes are formed by the escape of the protoplast of a vegetative cell from its enclosing cell wall. The clones forming smooth unornamented zygotes are described as a new species Chlamydomonas zimbabwiensis. In this species the investigation of the sexual process is facilitated by three distinct strains, a homothallic strain and two subheterothallic strains. A sexual hormone has been isolated and partically characterized from sperm filtrates which cause vegetative cells to escape from their cell walls and to function as naked female gametes. Four other strains having distinct zygote wall ornamentations appear to be interfertile and respond to the sexual hormone of C. zimbabwiensis as well. Cytological preparations of these strains as well as others in the subgenus Pleiochloris demonstrate the presence of large chromosomes which permit reasonably accurate counts. © 1979, VEB Gustav Fischer Verlag Jena. All rights reserved.