Cell wall characteristics during sexual reproduction of Mougeotia sp. (Zygnematophyceae) revealed by electron microscopy, glycan microarrays and RAMAN spectroscopy

Mougeotia spp. collected from field samples were investigated for their conjugation morphology by light-, fluorescence-, scanning- and transmission electron microscopy. During a scalarifom conjugation, the extragametangial zygospores were initially surrounded by a thin cell wall that developed into a multi-layered zygospore wall. Maturing zygospores turned dark brown and were filled with storage compounds such as lipids and starch. While M. parvula had a smooth surface, M. disjuncta had a punctated surface structure and a prominent suture. The zygospore wall consisted of a polysaccharide rich endospore, followed by a thin layer with a lipid-like appaerance, a massive electron dense mesospore and a very thin exospore composed of polysaccharides. Glycan microarray analysis of zygospores of different developmental stages revealed the occurrence of pectins and hemicelluloses, mostly composed of homogalacturonan (HG), xyloglucans, xylans, arabino-galactan proteins and extensins. In situ localization by the probe OG7-13AF 488 labelled HG in young zygospore walls, vegetative filaments and most prominently in conjugation tubes and cross walls. Raman imaging showed the distribution of proteins, lipids, carbohydrates and aromatic components of the mature zygospore with a spatial resolution of ~ 250 nm. The carbohydrate nature of the endo- and exospore was confirmed and in-between an enrichment of lipids and aromatic components, probably algaenan or a sporopollenin-like material. Taken together, these results indicate that during zygospore formation, reorganizations of the cell walls occured, leading to a resistant and protective structure.

Some Zygnemataceae (Chlorophyta) of Ontario, Canada, including descriptions of two new species

We examined 1455 filamentous algal samples collected from 32 Ontario sites since 1981 and identified 21 Zygnemataceae, including two new species: Spirogyra favosa Wei et Yung sp.nov. and Zygnema lacustre Wei et Yung sp.nov. Of the 21 taxa described in this paper, Zygogonium tunetanum, Temnogametum tirupatiense, Mougeotia quadragulata, and Spirogyra fennica were the important species in the acidic sites, whereas Mougeotia laetevirens, Zygnemopsis stephensiae, and Spirogyra jatobae were common in the circumneutral and alkaline locations. Zygogonium tunetanum was the most important metaphytic alga in lakes with pH 6.8 and lower, proliferating in the littoral areas of acidic Ontario lakes. These data support the view that the taxonomy of Zygnemataceae should place more emphasis on the zygospore wall structures and ornamentations and less emphasis on the dimensions of vegetative cells.

COMPLEMENTATION AND PRELIMINARY LINKAGE ANALYSIS OF ZYGOTE MATURATION MUTANTS OF THE HOMOTHALLIC ALGA, CHLAMYDOMONAS MONOICA

ABSTRACT Sexual reproduction in Chlamydomonas monoica is homothallic: pair formation and cell fusion occur in clonal culture and give rise to a heavily walled diploid zygospore. During maturation of the young zygote, a distinctive "primary zygote wall" is released before the development of the highly reticulate zygospore wall. Using ethyl methanesulfonate and ultraviolet irradiation as mutagens, we have isolated 19 maturation-defective (zym) mutant strains which upon self-mating produce inviable zygotes. These zygotes fail to release a primary zygote wall, fail to develop the normal zygospore wall, and eventually undergo spontaneous lysis. In nearly all cases, the mutations appear to be expressed only in the diploid zygote; pleiotropic effects on vegetative cell growth or morphology are not evident.—Complementation testing performed on 17 of these mutants indicates that all are recessive and that they define seven distinct complementation groups. Preliminary tetrad analysis of two-factor and multifactor zym crosses provides no evidence for physical clustering of the maturation genes, and instead suggests that they are widely distributed throughout the nuclear genome.