Howard J. Arnott

Processable polymers and copolymers of 3-alkylthiophenes and their blends

Abstract Poly(3-alkylthiophenes) have been prepared using anhydrous FeCl 3 in CHCl 3 while dry air was bubbled through the reaction mixture. Molecular weight studies via GPC, using polystyrene standards in conjunction with RI and UV detection along with absolute determinations using a multiangle laser light scattering (MALLS) detector, have shown these materials are of high molecular weight (M w of up to 400,000) and relatively low polydispersity ( M w M n ). Further, the MALLS detector (absolute molecular weights) provides weight average molecular weights 2–5 times larger than those obtained using polystyrene standards showing that polystyrene is a rather poor standard for these materials. A series of copolymers of the 3-alkylthiophenes was prepared using a 1:1 molar feed ratio of the two monomers and the molecular weights of the materials decreased with decreasing side chain length. Poly(3-alkylthiophenes) were processable via a variety of methods, including melt spinning to form soft fibers. The films and fibers were dopable with typical oxidants to conductivities of up to 5 Ω −1 cm −1 . The solution pulled fibers were observed to be birefringent with considerable orientation along the fiber axis. EDAX studies have shown that the doping of melt-spun Fibers was quite uniform. Blends of poly(3-decylthiophene) with low density polyethylene have been prepared and melt-spun into fibers. Blends prepared by melt-blending the components were seen by electron microscopy to be phase separated into large domains while those prepared from xylene solution were much more uniform. Spinning was easier with the blends and the fibers spun from the blend prepared from xylene solution was seen to be birefringent with considerable orientation along the fiber axis. Doping of the melt spun fibers obtained from xylene solution formed blends gave conductivities of ca. 10 −1 − 1 Ω −1 cm −1 while those produced from the melt formed blends were non-conducting.

Calcium oxalate crystal morphology and development in Agaricus bisporus

Aerial hyphae of Agaricus bisporus grown in agar culture, or on natural substrates like rye grain, produce abundant calcium oxalate crystals associated with the hyphal wall. These deposits, when first formed, consist of acicular crystals that cover the surface of the hyphae, giving the elements of the aerial mycelium a bottle-brush appearance. SEM examination of the crystal-bearing hyphae reveals that the crystals are arranged more or less tangentially on the hyphal surface. The crystals appear to originate within the wall of the hyphae, and as they increase in length their distal ends protrude through the hyphal wall. While the crystalline deposits of hyphae grown on malt-extract agar or on rye grain are typically elongate crystals, calcium oxalate deposits of hyphae grown on enriched media consist of both elongate forms and large, plate-like crystals. Scanning and transmission electron micrographs, energydispersive x-ray elemental analysis, and x-ray powder diffraction analysis of these crystals are presented.

Twinned Raphides of Calcium Oxalate in Grape (Vitis): Implications for Crystal Stability and Function

Among the higher plants that accumulate crystalline calcium oxalate, many taxa characteristically produce raphides, or needle‐shaped crystals. Substantial evidence has accumulated indicating that raphides function in plant defenses against herbivory and that their acicular shape is a critical component in proposed mechanisms for these defenses. Previous observations have shown that raphides in members of the Vitaceae are twinned crystals. In this study, the fine structure of raphides in Vitis was examined in order to determine the nature of twinning. Rotation of isolated raphides under cross‐polarized light revealed extinction patterns that indicated that raphides are twinned along their length. In cross sections of raphides, the twin plane extends across the raphides, parallel to their surfaces. The dissolution patterns observed in etched crystals indicate that the type of twinning is rotational. Parallels in other biomineralization systems indicate that the rotational nature of the twinning may increase mechanical strength. In addition, because twinning may affect crystal growth or enhance stability and persistence of crystals, it could be an important factor in allowing plant cells to produce the raphide morphology.

Calcium Oxalate Crystal Formation in the Bean (Phaseolus vulgaris L.) Seed Coat

The formation of calcium oxalate crystals in the developing bean seed coat was investigated by light, polarization, transmission, and scanning electron microscopy. Crystals first form in isolated lacunar parenchyma cells near the hilum, later in cells of subhilar tissue, and finally in hypodermal sclereid cells The initiation and development of crystals were studied in hypodermal sclereid cells Prior to crystal formation, young sclereid cells become highly vacuolate. Fibrillar material, as well as large vesicles apparently of cytoplasmic origin, appear in the vacuoles. Fusion or close association of these vesicles results in the formation of electron-dense bodies and membrane-like compartments (crystal chambers) within the vacuoles. Crystallization then commences within these chambers. Symmetrical prismatic twin crystals of calcium oxalate of two types form: kinked and straight twin crystals. The presence of an ordered substructure in crystal chamber sheaths indicates possible nucleation sites where crystallization occurs. Electron-dense bodies and fibrillar material within the vacuoles seem to be closely associated with crystal development. Mitochondria and plastids, the latter becoming transformed into crystalloplastids, also appear to be implicated in the crystallization process. Crystal growth is accompanied by thickening of cell walls which make contact with the crystals and begin to grow around them. After maximum crystal size and cell wall thickness have been attained, the remaining protoplast degenerates. Crystals in mature sclereid cells, surrounded by thick cell walls, could enhance the protective role of the bean seed coat.

Nannobacteria as a by-product of enzyme-driven tissue decay

Spheroidal features, 50 to 200 nm in size and found in sedimentary rocks, have been described as nannobacteria. The idea that they are minute fossilized life forms—and especially the discovery of such features in Martian meteorite ALH84001—sparked a lively debate with regard to identification of ancient microbial life. Because biologists consider 200–300 nm to be the lower viable size limit for microorganisms, an alternative explanation is needed for features that have been described as nannobacteria by geologists. We report here on tissue-decay experiments that produced abundant proteinaceous spheroids in the size range of nannobacteria (described as nannoballs in the remainder of this paper). Experimental conditions were comparable to those found in Earth9s surface sediments, and diagenetic mineralization of these spheroids may be a common process for preservation of nannoballs that are observed in the rock record.

MORPHOLOGY AND DEVELOPMENT OF CALCIUM OXALATE DEPOSITS IN GILBERTELLA PERSICARIA (MUCORALES)

Walls of sporangiophores and sporangia of Gilbertella persicaria contain conspicuous deposits of calcium oxalate. The morphology of these crystalline deposits varies with location on the fruiting structure. Deposits over most of the sporangiophore consist of elongate, flattened plates embedded in the sporangiophore wall, and these plates often bear single or paired, upright appendages. In the area of transition between sporangiophore and sporangium the crystals consist of short, verrucose projections borne on flattened, polygonal basal plates. Crystals on the sporangium proper are morphologically complex, composed of an apical, flattened, polygonal cap, an angular, upright column, and a flattened, polygonal base plate. Scanning electron micrographs and X-ray elemental analysis of these crystals are presented. The morphology of these crystals and their relationship to sporangiophore and sporangium development are discussed, along with speculations on the function of these deposits.

CALCIUM OXALATE CRYSTALS AND BASIDIOCARP DEHISCENCE IN GEASTRUM SACCATUM (GASTEROMYCETES)

Basidiocarps of Geastrum saccatum have calcium oxalate crystals associated with the peridium. In mature, opened basidiocarps eroded crystals occur on the outer surface of the endoperidium. Examination of undehisced basidiocarps reveals that bipyramidal calcium oxalate crystals arise from, and remain associated with, the hyphae that form the endoperidial layer. The development of calcium oxalate crystals in the endoperidial layer prior to basidiocarp dehiscence suggests that the formation of these crystals may be related to the process of exo- and endoperidial separation during basidiocarp maturation.

THE EFFECT OF CALCIUM ON MYCELIAL GROWTH AND CALCIUM OXALATE CRYSTAL FORMATION IN GILBERTELLA PERSICARIA (MUCORALES)

Patterns of calcium oxalate crystal development on sporangiophores and sporangia of Gilbertella persicaria are a consistent feature of this fungus when grown on a variety of standard mycological media. When grown on a liquid synthetic medium consisting of dextrose and salts, initial growth of the fungus and production of calcium oxalate crystals mimics growth on standard solid media. Soon, however, crystal production becomes aberrant, then ceases. Concomitant with the change in crystal morphology, growth of aerial portions of the colony increases dramatically. Normal colony morphology and crystal production are maintained when calcium salts are added to the synthetic medium. Significantly more fungal dry weight is produced on the synthetic medium when no calcium is added. Data gathered suggest that: 1) mineralized deposits may provide structural support; 2) early production of crystal-bearing sporangia lowers calcium concentrations in the medium sufficiently to alter and eventually stop calcium oxalate crystal production; 3) calcium may inhibit growth; 4) calcium oxalate crystal production in G. persicaria may regulate environmental calcium concentrations.

Zostera capensis setchell: Root structure in relation to function

Abstract Root structure of the seagrass Zostera capensis Setchell was investigated by light and electron microscopy. Roots possess conspicuous root hairs which greatly increase the surface area available for absorption. Exodermal cells abutting root-hair bases possess transfer cell characteristics. The strategic location of these cells suggests that they participate in absorptive and/or transfer processes between the epidermis and cortex. Vascular parenchyma cells within the stele also possess transfer cell features. Wall ingrowths of these cells about xylem elements, sieve tubes, companion cells and other vascular parenchyma cells, suggesting that they play a role in absorptive and/or transfer processes between the stele and cortex. Apoplastic barriers in the form of suberin lamellae and Casparian bands occur in walls of both the exodermis and endodermis. However, plasmodesmata perforate the suberin lamellae in these walls, and a symplastic pathway can be traced from the root hairs to vascular parenchyma transfer cells contiguous with conducting elements of the stele. The occurrence of wall ingrowths adjacent to xylem elements implies that transfer processes occur between vascular transfer cells and xylem. Although reduced, xylem could therefore play a role in transport. Structural evidence obtained in this study supports the role of the roots in absorptive processes and shows pathways available for transport from the water column to the conducting tissues of the root.

SEASONAL CHANGES IN STRUCTURE OF A SUBMERGED BLUEGREEN ALGAL/BACTERIAL COMMUNITY FROM A GEOTHERMAL HOTSPRING1

The species (cytospecies) structure and seasonal dynamics of a thermophilic bluegreen algal/bacterial community from Mimbres, New Mexico are described. Using stereological techniques, several common quantitative ecological parameters (biomass, density, distribution measurements, Species Diversity Indices, importance values) were described for the community growing ca. 1 m beneath the water surface on the inner walls of a concrete cistern. Temperature and pH were relatively constant while water flow rates, duration and intensity of light showed seasonal variation. The total volume of the mat occupied by living organisms did not exceed 2% during the entire year. The remaining volume was occupied by gas and water bubble chambers, gelatinous matrix, empty tubes, mineral deposits, and water. The total biomass remained constant except during a period of severe, seasonal light reduction (November). Species Diversity Indices, density and importance values for the bluegreen algal and bacterial populations showed seasonal changes. The three dominant bluegreen algal cytospecies which represented the greatest amount of biomass alternated in their abundance on a seasonal basis while the three dominant bacterial cytospecies remained the same throughout the period of study. Although considerable season change occurred in the species structure of this community, the total living volume remained relatively constant with the major changes in the bluegreen algal populations. Many of the seasonal changes observed appear to correlate with seasonal changes in light intensity and duration.