Phytophagous insects enhance nitrogen flux in a desert creosotebush community

Summary We tested the hypothesis that herbivorous insects on desert shrubs contribute to short-term nitrogen cycling, and increase rates of nitrogen flux from nutrient rich plants. Creosotebush (Larrea tridentata) shrubs were treated with different combinations of fertilizer and water augmentations, resulting in different levels of foliage production and foliar nitrogen contents. Foliage arthropod populations, and nitrogen in canopy dry throughfall, wet throughfall and stemflow were measured to assess nitrogen flux rates relative to arthropod abundances on manipulated and unmanipulated shrubs over a one-month period during peak productivity. Numbers and biomass of foliage arthropods were significantly higher on fertilized shrubs. Sap-sucking phytophagous insects accounted for the greatest numbers of foliage arthropods, but leaf-chewing phytophagous insects represented the greatest biomass of foliage arthropods. Measured amounts of bulk frass (from leaf-chewing insects) were not significantly different among the various treatments. Amounts of nitrogen from dry and wet throughfall and stemflow were significantly greater under fertilized shrubs due to fine frass input from sap-sucking insects. Increased numbers and biomass of phytophagous insects on fertilized shrubs increased canopy to soil nitrogen flux due to increased levels of herbivory and excrement. Nitrogen excreted by foliage arthropods accounted for about 20% of the total one month canopy to soil nitrogen flux, while leaf litter accounted for about 80%.     

Studies on the biosynthesis and metabolism of the phytoalexin lubimin and related compounds in Datura stramonium L.

Arachidonic acid, cellulase, CuSO₄, a sonicate of Phytophthora infestans mycelium and a spore suspension of Penicillium chrysogenum all elicited the formation of the sesquiterpenoid phytoalexins lubimin, 3-hydroxylubimin and rishitin in fruit cavities of Datura stramonium. 3-Hydroxylubimin was the predominant phytoalexin formed after treatment of the fruits with arachidonic acid, cellulase and the P. infestans preparation. Copper sulphate was a potent elicitor of lubimin but not 3-hydroxylubimin. The fungus P. chrysogenum metabolized lubimin and 3-hydroxylubimin to 15-dihydrolubimin and 3-hydroxy-15-dihydrolubimin respectively, both in fruit cavities inoculated with spores of this fungus and in pure culture. The 15-dihydrolubimin formed in the fruits by the fungus was further metabolized (by the fruits) to both isolubimin and 3-hydroxy-15-dihydrolubimin. The precursor-product relationships between all of the subject compounds was investigated by feeding experiments with ³H-labelled compounds. 2-Dehydro-[15-³H₁]lubimin was rapidly and efficiently incorporated into lubimin and may be the direct precursor of lubimin in planta. 3-Hydroxy[2-³H₁]lubimin was incorporated into the nor-eudesmane rishitin but 10-epi-3-hydroxy[2-³H₁]lubimin was not. An updated scheme for the biosynthesis and metabolism of lubimin and related compounds in infected tissues of solanaceous plants is presented.We thank Mr Vic Swetez for the provision of plant material, Mrs Margaret Huffee for technical assistance, Dr David Ewing for help with obtaining NMR spectra, and the Agricultural and Food Research Council for financial support.     

Social relationships between adult male and female rhesus macaques: II. non-sexual affiliative behaviour

The social relationships of adult male rhesus macaques (Macaca mulatta) in Group I of the Cayo Santiago colony were studied over a period of 14 months. Relationships were found in which adult males and sexually mature females were persistently close to one another in nonsexual contexts, both within and across seasons. Males of long tenure and high dominance rank tended to have more female partners, and more persistent relationships, than more recent immigrants of lower rank. Correlations with length of tenure were stronger than those with dominance rank. Closely-related females tended to have persistent relationships with the same male. In most cases the female was primarily responsible for maintaining proximity in non-sexual contexts. Dyads which were persistently within 5 m of each other in the birth season were more likely to form a consortship in the subsequent mating season than those which had a brief relationship. A similar tendency was apparent in the 1 m data but it was not statistically significant. There was no association between persistent proximity during the birth season and the occurrence of long, or multiple consortships, nor with the maintenance of proximity or direction of grooming between consort partners. The pattern of consortships was not closely related to the formation of persistent relationships in the subsequent birth season. Females occasionally received protection from their male partners and, in some cases, spent more time in the feeding corral with them than did other females. Affiliative relationships can be very enduring and may have long-term benefits that were not apparent during the study period.     

E infα supk transgene in B10 mice suppresses the development of myasthenia gravis

Mice bearing the H-2 ^bhaplotype are susceptible to the development of experimental autoimmune myasthenia gravis (EAMG), induced by acetylcholine receptor (AChR) autoimmunity. One of the genes influencing EAMG susceptibility has been mapped to the A ^blocus of the major histocompatibility complex, and the A chain has been implicated in the pathogenesis. Mice of the H-2 ^bhaplotype, including C57BL/10 (B10), have a genomic deletion of the E gene and therefore fail to express the E molecule on their cell surface. To test the hypothesis that failure to express the cell surface E molecule in B10 mice contributes to EAMG pathogenesis, E _inf ^supk transgenic B10 mice expressing the T molecule were examined. Expression of the E molecule in E _inf ^supk transgenic B10 mice partially prevented the development of EAMG.     

Effects of dl-2-Amino-5-Phosphonovalerate on Metabolism of Catecholamines in Synaptosomes from Rat Brain

Incubation of synaptosomes from rat brain with DL-2-amino-5-phosphonovalerate (APV) stimulated an increased release of dopamine, and this effect was strictly dependent on the extrasynaptosomal calcium level. APV increased biosynthesis of dopamine from tyrosine by 30%, whereas monoamine oxidase activity was inhibited by 30%. When synaptosomes were incubated with radioactive dopamine, APV caused a large decrease in incorporation of label into 3,4-dihydroxyphenylacetic acid but greatly increased incorporation into norepinephrine and its N-methyl derivatives. Quantification of dopamine and its metabolites in synaptosomes, using electrochemical detection, indicated that the presence of APV resulted in changes in the absolute levels of the aforementioned dopamine metabolites similar to the changes in radiolabel incorporation. Omission of Ca2+ from the extrasynaptosomal medium greatly diminished the APV-induced changes in catecholamine metabolism. The metabolic changes appear to largely result from an increased intrasynaptosomal Ca2+ level due to the APV-induced increase in calcium permeability of the plasma membrane.     

Solubilization and Mineralization of Lignin by White Rot Fungi

The white rot fungi Lentinula edodes, Phanerochaete chrysosporium, Pleurotus sajor-caju, Flammulina velutipes, and Schizophyllum commune were grown in liquid media containing ¹⁴C-lignin-labelled wood, and the formation of water-soluble ¹⁴C-labelled products and ¹⁴CO₂, the growth of the fungi, and the activities of extracellular lignin peroxidase, manganese peroxidase, and laccase were measured. Conditions that affect the rate of lignin degradation were imposed, and both long-term (0- to 16-day) and short-term (0- to 72-h) effects on the production of the two types of product and on the activities of the enzymes were monitored. The production of ¹⁴CO₂-labelled products from the aqueous ones was also investigated. The short-term studies showed that the different conditions had different effects on the production of the two products and on the activities of the enzymes. Nitrogen sources inhibited the production of both products by all species when differences in growth could be discounted. Medium pH and manganese affected lignin degradation by the different species differently. With P. chrysosporium, the results were consistent, with lignin peroxidase playing a role in lignin solubilization and manganese peroxidase being important in subsequent CO₂ production.     

Isolation, Cultural Maintenance, and Taxonomy of a Sheath-Forming Strain of Leptothrix discophora and Characterization of Manganese-Oxidizing Activity Associated with the Sheath

Leptothrix discophora SP-6 was isolated from the outflow reservoir of an artificial iron seep. Its sheathforming phenotype was maintained by slow growth in a mineral salts-vitamin-pyruvate medium under minimal aeration at 20 to 25°C. A sheathless variant, SP-6(sl), was isolated from smooth colonies that appeared on spread plates after rapid growth of SP-6 in well-aerated cultures. SP-6 and SP-6(sl) are closely related but not identical to the previously studied sheathless strain SS-1 (ATCC 43182). Increasing Mn²⁺ concentrations in the growth medium of SP-6 increased the phase density of the sheath, indicating increased Mn oxide deposition in the sheath. Electron microscopy of cultures grown without added Mn²⁺ revealed that the sheath consisted of a well-defined inner layer, 30 to 100 nm thick, and a diffuse outer capsular layer of variable thickness. Mn oxides were identified in the sheath by their characteristic ultrastructure, electron density, and X-ray-dispersive energy spectra. In heavily encrusted sheaths, the Mn oxides were evenly distributed in both layers of the sheath. Sheathed cells retained more Mn-oxidizing activity than did sheathless cells after washing with distilled, deionized water; the sheath retained some of its activity after an EDTA-lysozyme-detergent treatment which removed the cells. An ultrafiltration-dialysis procedure significantly increased the recovery of activity from spent media of SP-6 over that reported previously for SS-1 (L.F. Adams and W.C. Ghiorse, J. Bacteriol. 169:1279-1285, 1987). A 108-kDa Mn-oxidizing protein was identified in concentrated spent media of SP-6 and SP-6(sl), and the activity of the concentrates showed stability in detergents comparable to that of SS-1 and patterns of heat inactivation and chemical inhibition similar to those of SS-1.     

The use of amphipathic maleimides to study membrane-associated proteins

A series of amphiphilic polymethylenecarboxymaleimides has been synthesized for use as sulfhydryl reagents applicable to membrane proteins. Physical properties of the compounds which are relevant to their proposed mode of action have been determined. By comparing rates of reaction in aqueous and aprotic solvents, the compounds have been shown to react exclusively with the thiolate ion. The effects of the reagents on three membrane-associated proteins are reported, and in two cases a comparative study has been made of the effects on the proteins in the absence of membranes. A mechanism is proposed whereby the reagents are anchored at the lipid/water interface by the negatively charged carboxyl group, thus siting the reactive maleimide in a plane whose depth is defined by the length of the reagent. Supporting evidence for this model is provided by the inability of the reagents to traverse membranes, and variation of their inhibitory potency with chain length when the proteins are embedded in the membrane, but not when extracted into solution. As examples of general use of the reagents to probe sulfhydryl groups in membrane proteins, the reagents have been used to (a) determine the depths in the membrane at which two populations of sulfhydryl groups occur in the mitochondrial phosphate transporter; (b) locate a single sulfhydryl associated with the active site ofD--hydroxybutyrate dehydrogenase in the inner mitochondrial membrane; (c) examine sulfhydryl groups in theD-3-glyceraldehyde phosphate dehydrogenase associated with the human red blood cell membrane.