Effect of Seed Treatment on Growth and Growth-substance Content of Dwarf French Beans (Phaseolus vulgaris)

The longer the seeds of dwarf French bean (Phaseolus vulgaris)were soaked in water before sowing, the smaller were the seedlingsthey produced. Soaking for 24 hours removed only little drymatter, but detectable amounts of a gibberellin and a betaine.The amounts of these two removed increased with increased timeof soaking. Long soaking of seeds decreased the amounts of gibberelinand auxin in the cotyledons, and of gibberellin, auxin, andbetaine in the primary leaves of seedlings. Aerating, cooling,or increasing the volume of water in which the seeds were soakedalso retarded the growth of the seedlings, but did not affectthe amount of growth substance removed from the seeds or containedin the cotyledons. The deleterious effect of soaking seeds wasnot alleviated by treating the seeds or seedlings with gibberellicacid or glycine betaine. Although larger seedlings were producedby heavy than by light seeds, their cotyledons and primary leavescontained similar concentrations of growth substances.     

Molecular Markers for Ion Compartmentation in Cells of Higher Plants

The tonoplast plays a crucial role in ion compartmentation,which is a central feature of the salt tolerance of halophytes,but we do not know the properties of the membrane that conferthis ability. A method was, therefore, developed for the isolationof vacuoles from Suaeda maritima (L.) Dum. of sufficiently highpurity to enable biochemical characterization of their lipidand protein composition. Tonoplast fractions produced by densitygradient centrifugation, as well as vacuoles isolated by a varietyof methods (including DEAE dextran lysis, digitonin lysis, andmechanical shear forces) were unacceptably contaminated. A highlypure vacuole preparation was obtained when protoplasts werelysed by a mild hypotonic shock in alkaline buffer, in the presenceof the compatible cytosolute glycine-betaine, followed by shearforce during ultracentrifugation; cytoplasmic contaminationwas prevented by the addition of the zwitterionic detergent3-([3-cholamidopropyl]dimethylammonio)-l-propanesulphonate (CHAPS).Light microscopy of this preparation revealed no intact protoplastsand no contamination by chlorophyll could be detected. Electronmicroscopy showed the vacuoles to be single-membrane-bound structures,and was the only criterion upon which vacuoles could be separatedreliably from vacuoplasts, in which the plasmalemma is collapsedon to the tonoplast. Analysis by SDS-PAGE showed that a totalof 15 polypeptides were enriched in the tonoplast and 27 inthe soluble fraction from vacuole preparations, with a patternsimilar to that reported for glycophytic species. The pure tonoplastexhibited both vanadate-insensitive ATPase and pyrophosphataseactivities, but the properties of these enzymes were broadlysimilar to those of glycophytes. Analysis of membrane fattyacids showed that the degree of saturation of the putative tonoplastpreparation increased as the assessment of the purity of thepreparation (made by microscopy) increased. The ATPase couldbe substantially purified by ion-exchange FPLC. The resultsare discussed in relation to the degree of purity needed inmembrane preparations in order to be suitable for biochemicalanalysis. Key words: ATPase, membrane lipids, tonoplast, salinity, Suaeda maritima     

Spring feeding by pink-footed geese reduces carbon stocks and sink strength in tundra ecosystems

Tundra ecosystems are widely recognized as precious areas and globally important carbon (C) sinks, yet our understanding of potential threats to these habitats and their large soil C store is limited. Land‐use changes and conservation measures in temperate regions have led to a dramatic expansion of arctic‐breeding geese, making them important herbivores of high‐latitude systems. In field experiments conducted in high‐Arctic Spitsbergen, Svalbard, we demonstrate that a brief period of early season belowground foraging by pink‐footed geese is sufficient to strongly reduce C sink strength and soil C stocks of arctic tundra. Mechanisms are suggested whereby vegetation disruption due to repeated use of grubbed areas opens the soil organic layer to erosion and will thus lead to progressive C loss. Our study shows, for the first time, that increases in goose abundance through land‐use change and conservation measures in temperate climes can dramatically affect the C balance of arctic tundra.     

Herbivory in omnivorous fishes: effect of plant secondary metabolites and prey stoichiometry

1. Many animals that consume freshwater macrophytes are omnivorous (i.e., they include both plant and animal matter in their diet). For invertebrate omnivorous consumers, selection of macrophyte species depends partly on the presence of secondary metabolites in plants, plant carbon/nutrient balances and/or physical structure of plants. However, little is known about the mechanisms influencing consumption of macrophytes in aquatic vertebrates. 2. For two fish species, the omnivorous rudd (Scardinius erythrophthalmus) and herbivorous grass carp (Ctenopharyngodon idella), feeding preferences were determined in three choice experiments. We tested (i) whether the presence of secondary metabolites and macrophyte stoichiometry affects macrophyte species selection by fish, (ii) the importance of macrophyte stoichiometry by manipulating the macrophytes experimentally and (iii) the rate of herbivory when the most palatable macrophyte is offered simultaneously with a common animal prey. 3. In a choice experiment with five species of submerged macrophytes (Callitriche sp., Chara globularis, Elodea nuttallii, Myriophyllum spicatum and Potamogeton pectinatus), Myriophyllum was clearly consumed least by both fishes, which strongly correlated with the highest phenolic concentration of this macrophyte. Additionally, a significant negative relationship was found between consumption and C : N ratio of the five macrophytes. The two most consumed macrophytes also had the lowest dry matter concentration (DMC). 4. In a second choice experiment, the C : N ratio of the least (Myriophyllum) and most (Potamogeton) palatable plants was manipulated by growing the macrophytes under fertilised and unfertilised conditions and subsequently feeding them to rudd. The avoidance of consumption of the chemically defended Myriophyllum by rudd was partly alleviated by the lowered C : N ratio. 5. The third choice experiment showed that both fishes preferred animal prey (the amphipod Gammarus pulex) over the most palatable macrophyte (Potamogeton) when offered simultaneously. The C : N ratio of the amphipods was about half that of the lowest C : N ratio measured in the macrophytes. Consumption by the fishes could not clearly be related to C : P or N : P ratios of prey items in any of the experiments. 6. We conclude that omnivorous fish avoid macrophytes that are chemically defended. However, when these defences are only minor, stoichiometry (C : N ratio) in combination with DMC may be a determining factor for consumption by vertebrate facultative herbivores.     

Phylogeny of the tribe Sciophilini (Diptera: Mycetophilidae: Sciophilinae)

The monophyly and phylogenetic relationships within the species rich Sciophilini (Diptera: Mycetophilidae) were analysed, based on 96 adult morphological characters. The cladistic analysis included 80 Sciophilini exemplar species (representing all but 1 of the 36 genera placed previously in the Sciophilini) and 11 outgroup taxa of other mycetophilid tribes. The monophyly of Sciophilini was supported in the parsimony analysis by four synapomorphies. The tribe now contains 34 genera: Acnemia Winnertz, Acomoptera Vockeroth, Adicroneura Vockeroth, Afrocnemia Matile, Allocotocera Mik, Anaclileia Meunier, Aneura Marshall, Austrosciophila Tonnoir, Azana Walker, Baeopterogyna Vockeroth, Cluzobra Edwards, Drepanocercus Vockeroth, Duretophragma Borkent gen.n. , Eudicrana Loew, Leptomorphus Curtis, Loicia Vockeroth, Megalopelma Enderlein, Monoclona Mik, Morganiella Tonnoir & Edwards, Neoallocotocera Tonnoir, Neoaphelomera Miller, Neotrizygia Tonnoir & Edwards, Neuratelia Rondani, Paramorganiella Tonnoir, Paratinia Mik, Paratrizygia Tonnoir, Parvicellula Marshall, Phthinia Winnertz, Polylepta Winnertz, Sciophila Meigen, Stenophragma Skuse, Tasmanina Tonnoir, Taxicnemis Tonnoir & Edwards, and Trizygia Skuse. Four genera placed previously in Sciophilini (Coelophthinia Edwards, Impleta Plassmann, Speolepta Edwards and Syntemna Winnertz) are transferred to the Gnoristini. Neoneurotelia Shinji and Neoparatinia Shinji are considered nomina dubia . Diagnoses are given for all genera in the tribe. Duretophragma gen.n. is described for the following species (all of which are comb.n. ): Duretophragma andina (Duret), Duretophragma argentina (Duret), Duretophragma glabanum (Johannsen), Duretophragma fusca (Edwards), Duretophragma humeralis (Edwards), Duretophragma intermedia (Edwards), Duretophragma longifurcata (Freeman) (type species), Duretophragma morigenea (Edwards), Duretophragma naumanni (Duret), Duretophragma nigricauda (Edwards), Duretophragma obscura (Duret), Duretophragma ochracea (Freeman), Duretophragma pleuralis (Edwards) and Duretophragma similis (Johannsen). Other new generic combinations include: Trizygia albidens (Oliveira & Amorim) comb.n. , Trizygia alvesi (Oliveira & Amorim) comb.n. , Trizygia balbi (Oliveira & Amorim) comb.n. , Trizygia camargoi (Oliveira & Amorim) comb.n. and Afrocnemia stellamicans (Chandler) comb.n .     

Promotion of flowering in the Pinaceae by gibberellins

Significant female flowering of 6- to 11-year-old seedlings and grafted ramets of sexually mature scions of lodgepole pine (Pinus contorta Dougl.) was promoted by both topical and spray applications of a gibberellin (GA) A_4/7 mixture (1.6 to c. 5 mg per plant in total) during that period (June to September) when sexual differentiation of lateral primordia would be expected to take place. Girdling was used in most experiments to enhance the GA_4/7 effect, as was the auxin, naphthaleneacetic acid (NAA). Average frequency of flowering branches on treated plants over all experiments ranged from 27 to 59% (control ranged from 0 to 36%) and average number of female strobili was increased from 2- to 6-fold by growth regulator treatment, relative to controls. Within an experiment, clonal or family frequency of flowering for treated plants ranged from 11 to 67% (controls were 0 to 28%), and number of female strobili was increased from 2- to 14-fold by growth regulator treatment, relative to controls. Movement of the flowering stimulus from the point of application was apparent in several experiments, the response in adjacent branches being correlated positively with increasing dosage of GA_4/7. Significant male flowering occurred only in one experiment, girdling and GA_4/7 treatment being promotive factors. The use of spray applications of GA_4/7+ NAA is warranted to induce early and enhanced flowering in lodgepole pine seedlings and vegetative propagules for genetic improvement programs.     

Variability in temperature regulation of CO2 fluxes and N mineralization from five Hawaiian soils: implications for a changing climate

We examined the possibility that microbial adaptation to temperature could affect rates of CO₂, N₂O and CH₄ release from soils. Laboratory incubations were used to determine the functional relationship between temperature and CO₂, N₂O and CH₄ fluxes for five soils collected across an elevational range in Hawaii. Initial rates of CO2 production and net N mineralization increased exponentially from 15 °C to 55 °C; initial rates of CH₄ and N₂O release were more complex. No optimum temperature (in which rates decline at higher and lower temperatures) was apparent for any of the gases, but respiration declined with time at higher temperatures, suggesting rapid depletion of readily available substrate. Mean Q₁₀S for respiration varied from 1.4 to 2.0, a typical range for tropical soils. The functional relationship between CO₂ production and temperature was consistent among all five soils, despite the substantial differences in mean annual temperature, soils, and land-use among the sites. Temperature responses of N₂O and CH₄ fluxes did not follow simple Q₁₀ relationships suggesting that temperature functions developed for CO₂ release from heterotrophic respiration cannot be simply extrapolated. Expanding this study to tropical heterotrophic respiration, the flux is more sensitive to changes in Q₁₀ than to changes in temperature on a per unit basis: the partial derivative with respect to temperature is 2.4 Gt C ·° C^?1 with respect to Q₁₀, it is 3.5 Gt C · Q₁₀ unit^?1. Therefore, what appears to be minor variability might still produce substantial uncertainty in regional estimates of gas exchange.