Effects of fire,topography and year-to-year climatic variation on species composition in tallgrass prairie

Native unploughed tallgrass prairie from Konza Prairie, Kansas, USA is described with respect to plant species compositional changes over a five year period in response to fire and topography. The principal gradient of variation in the vegetation is related to time since burning. Species show an individualistic response in terms of relative abundance to this gradient. Both the percentage of and cover of C₄ species and all grasses decrease as the prairie remains unburnt. Forb and woody plant species numbers and abundance increase along this gradient. A secondary gradient of variation reflects topography (i.e. upland versus lowland soils). Upland soils support a higher species richness and diversity. Upland and lowland plant assemblages are distinct except on annually burnt prairie. The interaction between burning regime, topography and year-to-year climatic variation affects the relative abundance of the plant species differentially. The most dominant species overall, Andropogon gerardii, was affected only by year-to-year variation (i.e. climate). Its position at the top of the species abundance hierarchy was unaffected by burning regime or soil type. The other dominant species showed a suite of varying responses to these factors.Deceased May, 1986.     

Methanogenesis from methanol in Methanosarcina barkeri studied using membrane inlet mass spectrometry

Abstract A mass spectrometer with membrane inlet was used to study methanol metabolism by Methanosarcina barkeri strain MS. The addition of methanol to methanol grown culture samples in the mass spectrometer vessel stimulated methanogenesis and hydrogen production. The apparent K _s for methanol was determined as 0.5 mM and the V _max as 8.14 mmol g (dry weight) h⁻¹. The V _max for methane production was fairly constant during growth of the culture on methanol implying that growth is tightly coupled to methanogenesis. The addition of methanol to culture samples in the mass spectrometer vessel stimulated methanogenesis with no lag which indicated that methanogenesis can be uncoupled from growth. Exposure of the culture sample in the mass spectrometer vessel to an atmosphere of 2 kPa oxygen for 80 min resulted in a decrease in the rate of methanogenesis from methanol but on returning the atmosphere to nitrogen the addition of further methanol stimulated methanogenesis. The effect of other inhibitors of methanogenesis (2-bromoethane sulphonate and monensin); K _j values 21.5 μM and 0.3 mM, respectively) were also studied.     

Murine epidermal growth factor: heterogeneity on high resolution ion-exchange chromatography

We have shown that epidermal growth factor (EGF) purified either by the classical method of Savage and Cohen, or solely by h.p.l.c. techniques can be resolved into two species, EGF alpha and EGF beta. However, despite the apparent purity of such materials, as determined both chromatographically and by amino acid analysis, they failed to give homogeneous products on radioiodination. Analysis by isoelectric focusing on agarose gels followed by transfer to nitrocellulose and silver staining showed that EGF alpha could be further resolved into three sub-species which focused at pH 4.6, 4.3 and 4.1. EGF beta (which also focused at pH 4.6) contained very small amounts of the species with isoelectric points of 4.1 and 4.3, probably due to slight contamination of this preparation by EGF alpha. Preparative separation of the sub-species of EGF alpha was achieved by high performance anion-exchange chromatography at pH 6.5 on a Pharmacia Mono Q column. Radioiodination of these purified sub-species did not produce significant charge heterogeneity. However, two slightly different forms of [125I]EGF alpha 1 (pH 4.6 species) were separable by anion-exchange chromatography on the Mono Q column. All of the EGF species competed for binding to EGF receptors on A431 cells and were active mitogens for BALB/c 3T3 fibroblasts.     

New Class of Streptomycin-Resistant Mutants Incompatible with supX Suppressor Mutations in Salmonella typhimurium

Streptomycin-resistant colonies of Salmonella typhimurium appearing in platings of supX suppressors of strain leu-500 are less variegated in size than are those derived from strain leu-500 counterparts. Several of the streptomycin-resistant leu-500 clones, furthermore, yield suppressors and revertants of the leu-500 auxotrophy at unusually low rates, suggesting that they provide a genetic background inimicable to supX suppression. Two such "suppression-restrictive" leu-500 streptomycin-resistant (str) mutants, designated strains M(1) and M(4), were characterized as to their ability to receive the trp-supX-cysB linkage region by transduction. Coentry of a donor supX deletion mutation with the selected trp(+) marker was not observed even though these sites display more than 10% linkage in control experiments. This was demonstrably the result of nonviability of the combined supX mutant, M(1) or M(4) streptomycin-resistant genotype, rather than the lack of suppression of the leu-500 imparted auxotrophy. Both M(1)- and M(4)-type resistance was accompanied by pleiotropic effects resembling those caused by strB (nonribosomal)- rather than strA (ribosomal)-type resistance, but both restrictive mutants had a high upper limit of resistance corresponding to that of strA-type mutants. Transduction analyses indicated that the str character of neither the M(1) nor the M(4) strain was linked to the strA or the strB gene. These mutations define a previously undescribed locus, which we propose to designate strC, apparently related to streptomycin uptake rather than its intracellular action. Mutation at this locus is evidently incompatible with the inactivation or removal of the supX site, suggesting a functional association between products of the genes.     

Some novel flavin-nicotinamide biscoenzymes and their reactivities

The present study was undertaken to investigate flavin-nicotinamide reactions and interactions. A series of novel flavin-nicotinamide biscoenzymes have been synthesized by a general three-step procedure. The structures of these compounds were confirmed by nuclear magnetic resonance spectra, absorption spectra and elemental analysis. These compounds consist of short linear hydrocarbon chains interconnecting the N-1 of nicotinamide and the N-10 of the 7,8-dimethyl-isoalloxazine ring. The compounds were reduced with sodium dithionite (Na₂S₂O₄) and the flavin portion was reoxidized with ferricyanide. Re-reduction of the flavin portion by the nicotinamide portion of the molecule was followed anaerobically at 442 nm. When the interconnecting hydrocarbon chain was unsaturated, a second order reaction was observed with a rate equal to that of lumiflavin and 1-propyl-1,4-dihydronicotinamide (NprNicH₂) under the same conditions. When the two halves of the biscoenzymes were connected by saturated three- and four-carbon chains, the expected unimolecular reaction was not observed. Instead, the reduced biscoenzyme, after separation from excess sodium dithionite, was shown to have a strong absorption at 298 nm. This absorption is characteristic of hydration of dihydronicotinamides at the 5,6-double bond.In further studies, the C₃-biscoenzyme exhibited an absorption at 600 nm due to a complex between the reduced flavin and oxidized nicotinamide portions of the molecule. Absorbance at 600 nm increased linearly with the C₃-biscoenzyme concentration, clearly indicating that this is an intramolecular complex. When the C₃-biscoenzyme was at 0°C in 60–75% dimethylformamide buffer solution, no absorption at 600 nm was observed. When excess dithionite was removed, the spectrum under these conditions showed definite peaks at 297 and 357 nm. These respective peaks were attributed to hydrated dihydronicotinamide and dihydronicotinamide species present in the reaction mixture.The reduced flavin was postulated to be a catalyst for the hydration of dihydronicotinamide. This hypothesis was tested by incubating 1-propyl-1,4-dihydronicotinamide alone and with several concentrations of reduced riboflavin under basic anaerobic conditions. The results show that the reduced flavin increases the rate of disappearance of the dihydronicotinamide species and that the product shows an absorption near 298 nm. These results indicate that a reduced form of the flavin nucleus catalyzes the hydration of dihydronicotinamides.     

The circular dichroism of poly d(AAT): d(ATT) and poly r(AAU):r(AUU). A test of the first-neighbor hypothesis

We present absorption and circular dichroism (CD) spectra for the synthetic polymers poly d(AAT):d(AAT) and poly r(AAU):r(AAU), in both native and heat-denatured forms. As a means of evaluating the first-neighbor hypothesis, the CD spectra are compared with approximations derived from spectra of other synthetic polymers containing the same first-neighbor sequences. This is the first instance where such a comparison has been possible using spectra of double-stranded RNA sequences, and the agreement between the measured and approximated spectra for poly r(AAU):r(AUU) is surprisingly good. We have also subjected the CD spectrum of poly d(AAT):d(AAT) to a previously published analytical procedure for obtaining estimates of first-neighbor frequencies. In this first independent test of the procedure, we find that the analysis does infer the existence of a majority (86%) of AA, TT, AT, and TA first neighbors but does not precisely indicate their relative proportions.     

Sedimentation studies on the interaction of proflavine with deoxyribonucleic acid

A method is described of using photography to measure the concentrations of a small ligand (proflavine) above and below the boundary of a macromolecule (DNA, both native and denatured) sedimenting in the ultracentrifuge. The measurements are used to determine the extent of the binding of proflavine to DNA, and the results compared with those obtained by a spectrophotometric method. The results obtained by the two methods agree within 10%, thus validating the spectrophotometric technique under these conditions. The variation of the sedimentation coefficient with the extent of binding of proflavine was also studied. The results are discussed in relation to previously observed changes in the viscosity of the solutions.