Standing biomass and production in water drainages of the foothills of the Philip Smith Mountains, Alaska

In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra is the most widely distributed vegetation, and it occurs on rolling hills and in valleys that were shaped by a sequence of Pleistocene glaciations. In this study, aboveground standing biomass and production were compared in "intertrack tundra" areas that were relatively homogenous with respect to downslope drainage and adjacent "water tracks" that acted to channel water flow to the valley bottom stream. Comparisons of biomass, leaf area index, and specific leaf weight were also made between upper and lower slope positions. Similarities and differences of vegetation structure are examined with respect to graminoid, deciduous shrub, evergreen shrub, herbaceous, and bryophyte components.
Water tracks were found to have 1.5–1.7 times the biomass of intertrack tundra, and production (excluding secondary growth) in water tracks was 40% greater than in intertrack tundra. The aboveground biomass for all areas studied and the annual production values were similar to those found in other studies of tussock tundra. While only slight differences in depth of thaw occurred in water tracks and intertrack tundra during June and early July, water tracks thawed more deeply with the onset of summer rains. Warmer temperatures at 40 cm depth in July and August may have increased nutrient availability, whereas greater rooting depth and movement of water may have increased nutrient capture in water tracks as compared with the intertrack areas. Greater biomass and a deeper thaw depth occurred at upper slope locations.     

Structural basis for variations in the sensitivity of human decay accelerating factor to phosphatidylinositol-specific phospholipase C cleavage.

Human decay-accelerating factor (DAF) proteins expressed on E and nucleated cells differ in their susceptibility to phosphatidylinositol (PI)-specific phospholipase C (PLC) cleavage/release. To investigate the mechanism of this difference, the glycoinositol-phospholipid anchoring moieties of E DAF, and of HeLa cell, polymorphonuclear cell, and lymphocyte DAF were structurally compared. Labeling of PI-PLC-resistant E DAF with 3-(trifluoromethyl)-3-(m-[125I]-iodophenyl)-diazirine ([125I]TID) and TLC analysis of nitrous acid deamination anchor fragments showed a predominant phospholipid species with less polar migration than the 125I-TID-labeled PI. Gas chromatographic analyses of methanolyzed E protein revealed 2.20 +/- 0.16 mol of fatty acids [16:0, 18:0, 18:1, 20:4, 22:4, and 22:5 (0.76, 0.36, 0.25, 0.15, 0.40, 0.28 mol, respectively)] and 0.86 +/- 0.05 mol of inositol per mol of N-terminal Asp. Gas chromatography-mass spectroscopy demonstrated principally myo-inositol but also variable amounts of the chiro-isomer. Nondenaturing polyacrylamide gel electrophoresis of 14C-radiomethylated E protein revealed that pretreatment with hydroxylamine, a reagent which removes ester-linked lipids, rendered it PI-PLC susceptible. In contrast, parallel analyses of 35S-cys-labeled PI-PLC-sensitive HeLa DAF protein revealed only minor amounts of the hydroxylamine-sensitive phospholipid species. Similar results were obtained with 125I-surface-labeled DAF from polymorphonuclear cells, as well as from unstimulated peripheral blood and anti-CD3-activated lymphocytes. These findings demonstrate that, rather than PI, the E DAF anchor contains an inositol alkylacylglycerol-phospholipid which is heterogeneous with respect to acyl groups and inositol isomers, that an ester-linked substitution in this inositolphospholipid underlies the resistance of E DAF protein to PI-PLC cleavage/release, and that this structural modification is cell-specific.     

Fusion of cultured dog kidney (MDCK) cells: I. Technique,fate of plasma membranes and of cell nuclei

Summary The evaluation of the intracellular signal train and its regulatory function in controlling transepithelial transport with electrophysiological methods often requires intracellular measurements with microelectrodes. However, multiple impalements in epithelial cells are hampered by the small size of the cells. In an attempt to avoid these problems we fused cells of an established cell line, Madin Darby canine kidney cells, originally derived from dog kidney, to giant cells by applying a modified polyethylene glycol method. During trypsin-induced detachment from the ground of the petri dish, individual cells grown in a monolayer incorporate volume and mainly lose basolateral plasma membrane by extrusion. By isovolumetric cell-to-cell fusion, spherical giant cells are formed within 2 hr. During this process a major part of the individual cell plasma membranes is internalized. Over three weeks following cell plasma membrane fusion degradation of single cell nuclei and cell nuclear fusion occurs. We conclude that this experimental approach opens the possibility to investigate ion transport of epithelia in culture by somatic cell genetic techniques.     

Evaluation of a method to measure conjugal transfer of recombinant DNA in soil slurries

Release of recombinant microbes into the environment necessitates an evaluation of their ability to transfer genetic material. The present report evaluates a method to detect conjugal DNA plasmid transfer in soil slurries under various environmental conditions. DonorPseudomonas cepacia containing pR388::Tn1721 andP. cepacia recipient cultures were coincubated in soil slurries containing autoclaved or natural soil and treated with one or more of 14 experimental conditions. Conjugal mating frequency (transconjugants per initial donor) ranged from 4.8×10^–1 to 1.9×10^–7. Highest numbers of transconjugants, 1.5×10⁷ colony forming units/ml soil slurry, were observed following incubation at 35°C with an enriched nutrient supplement added to the soil. Low numbers of transconjugants, 10³ colony forming units/ml soil slurry, were observed when mating pairs were subjected to low nutrient or pH stress even though initial donor and recipient populations were maintained at high levels. This test system provides a simple way to estimate effects of changing environmental factors on plasmid transfer rates and on the survival of recombinant microorganisms. By use of soil collected from sites proposed to receive genetically engineered microorganisms, preliminary risk assessments can be obtained regarding the potential for gene transfer and microorganism survival with this soil slurry test system.     

Evidence for a two-step mechanism involved in assembly of functional signal recognition particle receptor

The signal recognition particle (SRP) and SRP receptor act sequentially to target nascent secretory proteins to the membrane of the ER. The SRP receptor consists of two subunits, SR alpha and SR beta, both tightly associated with the ER membrane. To examine the biogenesis of the SRP receptor we have developed a cell-free assay system that reconstitutes SR alpha membrane assembly and permits both anchoring and functional properties to be assayed independently. Our experiments reveal a mechanism involving at least two distinct steps, targeting to the ER and anchoring of the targeted molecule on the cytoplasmic face of the membrane. Both steps can be reconstituted in vitro to restore translocation activity to ER microsomes inactivated by alkylation with N-ethyl-maleimide. The characteristics elucidated for this pathway distinguish it from SRP-dependent targeting of secretory proteins, SRP-independent ER translocation of proteins such as prepromellitin, and direct insertion mechanisms of the type exemplified by cytochrome b5.     

The role of litter in an old-field community: impact of litter quantity in different seasons on plant species richness and abundance

Summary We studied the effect of removing and adding plant litter in different seasons on biomass, density, and species richness in a Solidago dominated old-field community in New Jersey, USA. We removed all the naturally accumulated plant litter in November (658 g/m²) and in May (856 g/m²) and doubled the amount of litter in November and May in replicated plots (1 m²). An equal number of plots were left as controls. Litter removal and addition had little impact on total plant biomass or individual species biomass in the growing season following the manipulations. Litter removal, however, significantly increased plant densities but this varied depending upon the season of litter removal, species, and life history type. Specifically, the fall litter removal had a much greater impact than the spring litter removal suggesting that litter has its greatest impact after plant senescence in the fall and prior to major periods of early plant growth in spring. Annual species showed the greatest response, especially early in the growing season. Both spring and fall litter removal significantly increased species richness throughout the study. Litter additions in both spring and fall reduced both plant densities and species richness in June, but these differences disappeared near the end of the growing season in September. We concluded than in productive communities where litter accumulation may be substantial, litter may promote low species richness and plant density. This explanation does not invoke resource competition for the decline in species richness. Finally, we hypothesize that there may be broad thresholds of litter accumulation in different community types that may act to either increase or decrease plant yield and diversity.     

Actinocamax primus arkhangelsky (belemnitellidae; upper cretaceous) biometry,comparison and biostratigraphy

A sample ofActinocamax primus Arkhangelsky, 1912 from the Lower Middle Cenomanian limestones of the Wunstorf quarry west of Hannover (NW Germany) is studied by univariate and bivariate biometric methods in order to analyse the variation of critical characters.A. primus is closely related toA. plenus (Blainville, 1825) but differs from that species by being smaller and more slender.A. primus appears in the Lower Cenomanian and continues into the Lower Middle Cenomanian. It is mainly distributed in the northern part of the North European Palaeobiogeographic Province.A. plenus is recorded from the Middle Cenomanian-lower Lower Turonian of the Russian Platform, but only from the Middle Upper Cenomanian in NW Europe. It is widespread in the North European Province.The primus event in the Lower Middle Cenomanian and theplenus event in the Middle Upper Cenomanian are briefly discussed.     

Genetic structure of the population of Sicily.

Genetic heterogeneity within Sicily was investigated on the basis of ACP1, ADA, ESD, GLO1, PGD, PGM1, PGM2, SODA, ABO, and MN gene frequencies, and compared to those of other regions of Italy for which these same loci have been examined. Correspondence analysis revealed no differences within the island, at least at the provincial level, but showed genetic differentiation among Italian regions, distinctly clustering northern, central, and southern populations, respectively. These data indicate a close relationship between Sicily and southern Italy. In addition, the contribution of Middle Eastern populations to the gene pool of Sicily was evident.     

Fluorescence-detected assembly of the signal recognition particle: binding of the two SRP protein heterodimers to SRP RNA is noncooperative.

Protein-RNA and protein-protein interactions involved in the assembly of the signal recognition particle (SRP) were examined using fluorescence spectroscopy. Fluorescein was covalently attached to the 3'-terminal ribose of SRP RNA following periodate oxidation, and the resulting SRP RNA-Fl was reconstituted into a fluorescent SRP species that was functional in promoting translocation of secretory proteins across the membrane of the endoplasmic reticulum. Each of the two protein heterodimers purified from SRP elicited a substantial change in fluorescein emission upon association with the modified RNA. The binding of SRP9/14 to singly-labeled SRP RNA-Fl increased fluorescein emission intensity by 41% at pH 7.5 and decreased its anisotropy from 0.18 to 0.16. The binding of SRP68/72 increased the fluorescein anisotropy from 0.18 to 0.23 but did not alter the emission intensity of SRP RNA-Fl. These fluorescence changes did not result from a direct interaction between the dye and protein because the fluorescein remained accessible to both iodide ions and fluorescein-specific antibodies in the complexes. The spectral changes were elicited by specific SRP RNA-protein interactions, since (i) the SRP9/14- and SRP68/72-dependent changes were unique, (ii) an excess of unlabeled SRP RNA, but not of tRNA, blocked the fluorescence changes, and (iii) no emission changes were observed when SRP RNA-Fl was titrated with other RNA-binding proteins. Each heterodimer bound tightly to the RNA, since the Kd values determined spectroscopically and at equilibrium for the SRP9/14 and the SRP68/72 complexes with SRP RNA-Fl were less than 0.1 and 7 +/- 3 nM, respectively. The binding affinity of SRP68/72 for SRP RNA-Fl was unaffected by the presence of SRP9/14, and hence the binding of the heterodimers to SRP RNA is noncooperative in the absence of SRP54 and SRP19. The SRP protein heterodimers therefore associate randomly and independently with SRP RNA to form domains in the particle that are distinct both structurally and functionally. Any cooperativity in SRP assembly would have to be mediated by SRP54 and/or SRP19.