Transmembrane segments of syntaxin line the fusion pore of Ca2+-triggered exocytosis

The fusion pore of regulated exocytosis is a channel that connects and spans the vesicle and plasma membranes. The molecular composition of this important intermediate structure of exocytosis is unknown. Here, we found that mutations of some residues within the transmembrane segment of syntaxin (Syx), a plasma membrane protein essential for exocytosis, altered neurotransmitter flux through fusion pores and altered pore conductance. The residues that influenced fusion-pore flux lay along one face of an alpha-helical model. Thus, the fusion pore is formed at least in part by a circular arrangement of 5 to 8 Syx transmembrane segments in the plasma membrane.     

Immunohistochemical localization in the rat brain of the precursor for thyrotropin-releasing hormone

A rabbit antiserum to a peptide sequence present in the precursor for thyrotropin-releasing hormone (proTRH), deduced from cloned amphibian-skin complementary DNA, was raised by immunization with the synthetic decapeptide Cys-Lys-Arg-Gln-His-Pro-Gly-Lys-Arg-Cys (proTRH-SH). Immunohistochemical studies on rat brain tissue showed staining of neuronal perikarya in the parvicellular division of the paraventricular nucleus of the hypothalamus and the raphe complex of the medulla, identical to that already described for thyrotropin-releasing hormone (TRH). Immunostaining was abolished by preincubation with proTRH-SH (10(-6)M) but not TRH (10(-5)M). Both TRH precursor and TRH were located in neurons of the paraventricular nucleus. However, in contrast to the findings for TRH, no staining was observed in axon terminals of the median eminence. These results suggest that a TRH precursor analogous to that reported in frog skin is present in the rat brain and that TRH in the mammalian central nervous system is a product of ribosomal biosynthesis.     

Characterization of intergeneric hybrids of <Emphasis Type="Italic">Erianthus rockii</Emphasis> and <Emphasis Type="Italic">Saccharum</Emphasis> using molecular markers

Erianthus rockii, a wild relative of sugarcane, is drought and cold tolerant, and both are potentially important agronomic traits to the sugarcane industry worldwide. As such it is of interest as a source of parental germplasm to sugarcane breeders and is currently being used in sugarcane introgression programs in both China and Australia. To date morphological characters have been used to verify the putative hybrids produced. Two crosses were generated between two different Saccharum species and two E. rockii accessions. Over 400 AFLP markers were used to identify the intergeneric hybrid progeny as well as determine hybrid diversity. Both crosses generated hybrids but efficiency levels were very different and are probably related to the different Saccharum parent used in each cross. Cross 1 was between a Saccharum officinarum and E. rockii and generated 100% hybrid progeny. Cross 2, however, was between a sugarcane hybrid (S. officinarum × Saccharum spontaneum) and E. rockii and only 10% of the progeny were intergeneric hybrids. Inheritance of markers in the progeny was analysed and for both crosses there were equal numbers of markers from both parents indicating n + n transmission of chromosomes. This is the first verification of E. rockii hybrids with molecular markers. It may now be possible to exploit genes of value from E. rockii in sugarcane breeding programs.     

Size and shape of fine quartz in the clay fraction of soils and geological materials

Fine clay fractions of two soils and five geological materials including three formed in late Wisconsinan glacial rock flour were separated by decantation and centrifugation procedures. X-ray diffractograms (XRD) showed mica and chlorite as the main components. Pyrosulfate fusion which removed the phyllosilicates and iron oxides revealed presence of quartz and some feldspars. After dilute H₂SiF₆ treatment, blade-shaped, platy and sheroidal particles mainly of 0.2–0.1 μm size were observed by scanning electron microscope. Fine feldspars and quartz were found to be susceptible to the chemical treatments. On treatment with diluted H₂SiF₆ + HF + H₃BO₃, the crystallinity of fine quartz was considerably decreased as indicated by a very broad diffraction maximum at a spacing of about 4 Å.     

Degradation Kinetics of Perchlorate in Sediments and Soils

This study investigated the intrinsic perchlorate (ClO₄ ^-)degradation kinetics of sediments and soils from multiple sites in microcosm studies, including the influence of varying nitrate concentration (NO₃ ^--N from 1 to 22.8 ppm) and up to 300 ppm sulfate. The first-order degradation rates and lag times of both ClO₄ ^- and NO₃ ^- degradation were site-specific and dependent on environmental conditions such as organic substrate availability, nitrate, initial ClO₄ ^- concentration, and prior ClO₄ ^- exposure. At an initial ClO₄ ^- concentration of 5 ppm, ClO₄ ^- degradation rates ranged from 0.13 to 0.46 day^-1, and lag times of ClO₄ ^- degradation ranged from 0 to 60.0 days; while NO₃ ^- degradation occurred at rates ranging from 0.03 to 1.42 day^-1, with lag times ranging from 0 to 29.7 days. Under the same treatment conditions, NO₃ ^- degradation rates were relatively higher than that of ClO₄ ^-. Perchlorate degradation rates remained constant at both lower (0.5 ppm) and higher (5 ppm) ClO₄ ^- concentrations. Generally, ClO₄ ^- rates were affected by the availability of organic substrate, which was represented here by Total Volatile Solids (TVS) of sediments and soils, and not by NO₃ ^-. Nitrate did increase the lag time of ClO₄ ^- degradation, which may account for the persistence of ClO₄ ^- in the environment, especially when ClO₄ ^- is typically ppb levels in the environment compared to ppm levels of NO₃ ^-. This study showed rapid intrinsic ClO₄ ^- degradation in sediments and soils of contaminated sites, and highlighted the potential for natural attenuation of ClO₄ ^- in the environment.     

Megaparks for metapopulations: Addressing the causes of locally high elephant numbers in southern Africa

Conservation management options for southern African elephants range from local to regional scales. Here we review these options and argue in favour of actions that will deal with the causes rather than symptoms of elephant numbers that are locally high. Metapopulation theory ensures population persistence, while our approach extends this in order to stabilise elephant numbers regionally. By allowing for the development and maintenance of regional sinks, we may also limit numbers in sources. This application of the metapopulation metaphor is a powerful ecological platform from which to manage elephant numbers and impact through southern Africa. Our approach engages the causes of the apparently high abundance of elephants in parts of southern Africa. It moves away from the practice of dealing only with numbers (symptoms) when managing the impact of elephants on other species. While providing an ecological basis for the development of elephant management options, this needs to be melded with social, political and economic realities through southern Africa. In this regard we are encouraged by the ongoing development of several Transfrontier Conservation programmes and Peace Parks across the region.     

Baseline element concentrations in soils and plants,Bull Island,Cape Romain National Wildlife Refuge,South Carolina,U.S.A.

Baseline element concentrations are given for Spanish moss (Tillandsia usneoides), loblolly pine (Pinus taeda), and associated soils. Baseline and variability data for ash, Al, Ba, C, Ca, Cd, Ce, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Na, Nb, Nd, Ni, P, Pb, S, Sc, Sr, Th, Ti, V, Y, and Zn are reported; however, not all variables are reported for all media because, in some media, certain elements were below the analytical detection limit. Spatial variation in element concentration among and within 0.5 km grid cells are given for each of the media. In general, only a few elements in Spanish moss showed statistically significant landscape patterns, whereas several elements in loblolly pine and in soils exhibited differences among sampling grids. Significant differences in the concentration of three elements in Spanish moss and eight elements (including total S) in loblolly pine were observed between two sampling dates (November and June); however, the absolute amount of these differences was small. Except for perhaps Ni and Pb concentrations in Spanish moss, element levels in all sample media exhibited ranges that indicate natural rather than anthropogenic additions of trace elements.     

The transfer of cadmium from sewage-sludge amended soils into the edible components of food crops

Water, Air, & Soil Pollution - The application of sewage sludge to soils used for the production of food crops represents a potential means by which human dietary exposures to Cd may be...     

Effects of arsenic on nutrient dynamics of grassland microcosms and field plots

Grassland field plots were compared to two sizes of excised microcosms (15 and 30 cm diameter) and 30-cm diameter homogenized microcosms to assess the effects of As on soil-plant nutrient dynamics. The goal of this experiment was to determine the feasibility of using microcosms for screening chemicals which are potentially toxic to terrestrial ecosystems. All experimental units were treated with As, at rates of 0, 0.5, and 5.0 mg cm^?2, by superficial application of dissolved Na₂AsO₄. Calcium, PO₄-P, NO₃-N, dissolved organic carbon (DOC), and NH₄-N were determined in soil leachate and soil extracts. Greater loss of PO₄-P, NO₃-N, NH₄-N, and DOC occurred via soil leachate from microcosms treated with the greatest level of As relative to untreated microcosms. Field plots were unaffected by As treatment. Excised microcosms were found to be more representative of field plots in reflecting microbial dynamics than were homogenized microcosms. Thus excised microcosms were recommended for testing potentially hazardous chemicals.