Pleurotaenium

Abstract: By means of X-ray analysis with a stereo-scanning electron microscope, it has been demonstrated that the crystals enclosed in the terminal vacuoles of several species of the desmid genus Closterium are of barium and not calcium sulphate as previously reported. Barium sulphate has also been found in cells of Pleurotaenium and Micrasterias.

Abstract: The freshwater zones of the Warri/Forcados Estuaries contain a rich and diverse flora of tropical desmids, which compare favourably and show strong affinities with desmids from other parts of Africa, tropical South America, Southeast Asia, tropical Australia and the Indian sub-continent. In this study, ninety (90) taxa belonging to seventeen (18) elongate baculiform and colonial genera are described. Fifty (50) of the taxa have been described for the first time for Nigeria, while nineteen (19) of them are new to Africa. Part 1 in this series of studies was devoted to the desmid genera Euastrum and Micrasterias. Based on new findings, a new taxon, Pleurotaenium subcoronulatum (Turner) W. West & G.S. West var. spinulosum Opute var. nova. has been proposed.

Abstract: Pleurotaenium trabecula (Ehren.) Nageli is a placoderm desmid that commonly occurs in wetland biofilms of the southeastern Adirondacks (NY, USA). It often displays a distinctive habit whereby the cell remains attached to the substrate via the polar end of one semicell, while the remainder of the cell is suspended in the water column. In this study, we examined the extracellular matrix (ECM) of this alga to elucidate its adhesion mechanisms and postadhesion behavior. The ECM consists of the following: (i) an extracellular polymeric substance (EPS), which includes polyanionic and sulfated polysaccharides; (ii) a thin pectin-containing primary cell wall, which is quickly sloughed off after postcytokinetic semicell expansion; and (iii) a thick secondary cell wall that is perforated with a distinct pore complex. Each pore of this complex possesses an external network of densely aggregated fibrils. Selective solubilization and immunolabeling studies suggest that these fibrillar aggregates or “adhesion centers” (i.e., ACs) contain arabinogalactan protein and are involved in initial adhesion of the cell to a substrate. We propose that postinitial adhesion behavior entails localized secretion of EPS derived from a large pool of EPS-containing vesicles situated in the peripheral cytoplasm. As the EPS absorbs water, hygroscopic pressure breaks the connections between the ACs on the cell wall and substrate and allows a portion of a cell to lift up into the water column.

Abstract: Desmids from 12 freshwater resources in the northern part of Thailand were investigated during 2002 to 2003. A total of 91 taxa were found. They belonged to 17 genera: Actinotaenium, Spirotaenia, Netrium, Gonatozygon, Pleurotaenium, Closterium, Euastrum, Micrasterias, Cosmarium, Cosmocladium, Stuarastrum, Staurodesmus, Xanthidium, Teilingia, Spondylosium, Hyalotheca and Desmidium. The water qualities in all the water resources were classified as oligotrophic to meso-eutrophic by trophic status. The taxa that could possibly be used as bioindicators of trophic state were Staurastrum gutwinskii, Spondylosium pandurifoemae, Cosmarium capitulum, C. mediosrobiculatum var. egranutum, S. tortum, Closterium gracile var. elongatum, C. kuetzingii and Closterium dianae var. dianae. The most frequently found taxa were Staurastrum limneticum var. burmense, S. tetracerum var. tetraerum, Pleurotaenium trabecula, Closterium ehrenbergii var. ehrenbergii and C. kuetzingii. The rare taxa in this study were Actinotaenium sp. Spirotaenia condensata, Pleurotaenium burmense var. dacchense and Micrasterias apiculata. Forty-one taxa of desmids were identified as new records for Thailand.