THE PRESENCE OF CALLOSE IN THE PRIMARY ZYGOTE WALL OF CHLAMYDOMONAS MONOICA AND THE EFFECTS OF ITS DEGRADATION ON ZYGOTE DEVELOPMENT

Chlamydomonas monoica constructs a temporary primary wall around its developing zygotes. This study aimed to confirm callose as a component of the primary wall, as well as to note the effects of primary wall degradation on zygote development. Glucanase, specific for the β-1,3 glycosidic bonds comprising callose, was added to mating media at concentrations ranging from 5 to 1 mg ml⁻¹ and light microscope observations were made as the zygotes developed. The overall health of the zygotes was assessed by comparing their ability to germinate after exposure to chloroform vapors. The bright staining of the primary wall with aniline blue, specific for β-1,3 polysaccharides, suggested the presence of callose. This was further supported by the adverse effects of glucanase on zygote development. After mating, declining levels of intact zygotes were found as their maturation continued, and dead immature zygotes accumulated in the treated cultures. Twelve days after mating, when the zygotes were plated for germination, fully mature zygotes were identified in only the lowest of the six enzyme concentrations. In addition, germinating zygotes from the treated cultures showed increased sensitivity to killing by chloroform vapors relative to untreated zygotes. These results suggest that callose is a key component in the primary zygote wall, and that its degradation negatively affects zygote maturation. Electron microscopy will be used to help determine whether structural defects in the primary wall occur as a result of glucanase treatment, and whether such defects affect secondary zygospore wall assembly.