THE ZYGOSPORE WALL OF CHLAMYDOMONAS-MONOICA (CHLOROPHYCEAE) - MORPHOGENESIS AND EVIDENCE FOR THE PRESENCE OF SPOROPOLLENIN

Chlamydomonas monoica Strehlow is being developed as a model for genet ic analysis of zygospore morphogenesis, and many relevant mutant strai ns are available. To provide the basis for interpreting the ultrastruc tural phenotypes of zygospore mutants, an analysis of wall morphogenes is in wildtype zygospores of C. monoica was undertaken. Following synt hesis of a thick, fibrous, primary zygote wall, granular material accu mulated between the plasma membrane and the primary zygote wall and ag gregated into a repetitive array of electron-opaque fibrous stripes. A new wall layer, the outer layer of the secondary zygospore wall, firs t appeared as segments with a fibrous outer surface overlying a well-d efined band of electron-translucent material. These segments gave rise to an intact sheath adjacent to the plasma membrane. Beneath this she ath, electron-opaque material (forming the inner layer of the secondar y zygospore wall) accumulated unevenly and forced the surface sheath t o undulate, creating a pattern of peaks and valleys that was exposed t o the external environment by rupture and release of the primary zygot e wall. The zygospore wall included material resistant to degradation by potassium hydroxide, 2-aminoethanol, and acetolysis, but it was des troyed by exposure to chromic acid. These characteristics, in. combina tion with the autofluorescence of untreated zygospore walls and their failure to stain with phloroglucinol, suggest that sporopollenin may b e responsible for many of the resistant properties associated with the mature zygospore of Chlamydomonas.