OCCURRENCE AND PHYLOGENETIC SIGNIFICANCE OF “SPECIAL WALLS” AT MEIOSPOROGENESIS IN COLEOCHAETE

Within germinating zygotes of Coleochaete pulvinata, meiospores are individually surrounded by chamber walls which are ultrastructurally and chemically different from vegetative cell walls of the same species. Meiospore chamber walls exhibit the staining reactions typical of callose. They thus resemble the “special walls” present during sporogenesis in embryophytes. Their presence suggests that the charophycean green algal ancestors of land plants may have possessed spore development preadaptations influential in the evolution of walled spores, an important plant adaptation to terrestrial life.