The effect of predation on the structure and invasibility of assembled communities

Summary Fifty four microcosmic communities were assembled over 4 months from a 28-species source pool of phytoplankton using nine different invasion patterns each replicated six times. Three communities from each set of replicates then were invaded with a cladoceran that feeds on phytoplankton. All communities were then treated identically for an additional 4 months. In all nine invasion categories species richness was greater in predated communities. Predation opened communities to invasion by increasing the representation of infrequently sampled species at the expense of more common species. Invasion rate was four times more influential than predation and over eleven times more important than either invasion order or the timing pattern of interspecific arrivals in determining species richness in this system of communitites.     

Role of inositol trisphosphate as a second messenger in signal transduction processes: An essay

This essay attempts to summarize some of the best evidence for the role of inositol trisphosphate as a second messenger in signal transduction processes. The following aspects are addressed in the essay: (a) The synthesis of inositol trisphosphate and other inositol lipids, (b) Receptor-phosphatidylinositol bisphosphate phospholipase C coupling and the N-ras protooncogene, (c) Inositol trisphosphate and intracellular calcium, (d) Cell growth and oncogenes, (e) Receptors linked to the phosphatidylinositol cycle, (f) Phototransduction and (g) Interactions between inositol trisphosphate and other second messengers.Abbreviations Cyclic AMP Adenosine 3,5-cyclic monophosphate - Cyclic GMP Guanosine 3,5-cyclic monophosphate - DG sn, 1,2-Diacylglycerol - EGF Epidermal growth factor - GDP Guanosine diphosphate - GTP Guanosine triphosphate - IP Inositol 1-monophosphate - IP₂ Inositol 1,4-diphosphate - IP₃ Inositol 1,4,5-trisphosphate - PA Phosphatidic acid - PDGF Platelet-derived growth factor - PI Phosphatidylinositol - PIP Phosphatidylinositol 4-monophosphate - PIP₂ Phosphatidylinositol 4,5-bisphosphate - PIP₃ Phosphatidylinositol 3,4,5-trisphosphate - PLC Phospholipase C     

Physical fine mapping of genes underlying X-linked deafness and non fra(X)-X-linked mental retardation at Xq21

Summary Linkage studies and cytogenetically visible deletions associated with nonspecific X-linked mental retardation (XLMR) and a specific form of deafness (DFN3) have indicated that the genes responsible for these disorders are located at Xq21. Using DNA probes from this region, we have studied several overlapping deletions spanning different parts of Xq21. This has enabled us to assign the DFN3 gene and a gene for nonspecific XLMR to an interval that encompasses the locus DXS232 and that is flanked by DXS26 and DXS121.     

Homologous recombination between human immunodeficiency viral DNAs in cultured human cells: analysis of the factors influencing recombination

Recombination between HIV DNAs was analyzed using DNA transfection in cell cultures and the optimal conditions for efficient recombination were determined. Recombinant plasmid DNA substrates were constructed from HIV proviral DNAs and the success of recombination was measured by the production of viable hybrid virus. The process of recombination between HIV DNAs was shown to be i) dependent on homology between the truncated HIV DNAs and ii) maximum with concentrations of the truncated DNAs 3ug and above. HIV isolates with heterogeneity in their primary sequence, thus offer an ideal system for the analysis of the requirement of homologous recombination. In addition, recombination methodology would be useful for generating hybrid HIVs for the analysis of specific viral gene functions.     

"Metallothionein-like" metal complexes in angiosperms; their structure and function

Evidence for the presence of the metal-binding protein metallothionein, MT, in higher plants is equivocal. Although a number of MT-like metal complexes have been isolated from plants, the chemical structures of most of these compounds have not been fully elucidated. Recently a novel class of plant peptides, poly (γ-glutamylcysteinyl) glycines, (γEC)_nG, have been discovered. These peptides bind metal ions, and in the presence of such ions the amount of (γEC), G in plant cells increases. The presence of peptide bonds through the γ-carboxyl group of glutamate, rather than the α-carboxyl group, suggests that these peptides are not encoded by structural genes but are the products of biosynthetic pathways. Cells which are resistant to supra-optimal concentrations of certain metal ions over-produce (γEC)_n G. (γEC)_n G. may be functional analogues of MT. Whether or not some plants also produce MT is an important question which remains to be answered.     

Enhanced enzymatic hydrolysis of lignocellulosic biomass pretreated by low-pressure steam autohydrolysis

Summary The use of low-pressure steam autohydrolysis in the pretreatment of corn stover and hybrid poplar has been assessed. In terms of yield of prehydrolyzed solids, minimal by-product formation and extent of subsequent enzymatic saccharification, the results of low-pressure steam pretreatment were found to be as good as or better than those reported for more severe pretreatment processes. Almost complete saccharification of the cellulose in the prehydrolyzed biomass solids was obtained within 24h with a commercial cellulase preparation — Celluclast. The presence of grinding elements (glass beads) during the enzymatic hydrolysis was found to increase the extent of saccharification by 40% to 50% over controls without any grinding elements.     

Unexpected segregation ratios from male-linked translocations in the Mediterranean fruitfly,Ceratitis capitata (Diptera: Tephritidae)

Three male-linked translocations were isolated in the Mediterranean fruitfly, Ceratitis capitata (Wiedemann) which showed sex linkage for an autosomal pupal colour marker, white pupa (wp). The wild type allele (wp ^–) was translocated to the male-determining chromosome. Males emerge from wild type pupae (brown) and females from white pupac. These lines will be used to develop an automatic sexing system.During maintenance of these lines in large populations it was noted that in two of them there was a significant distortion in the expected 1: 1 segregation ratio for pupal colour and excess white pupae were produced. However, adults did not emerge from a large proportion of these pupae. Using known numbers of 1st instar larvae from the three lines, the distortion was further studied and the effect confirmed. To account for this pupal colour segregation distortion it was assumed that certain duplication/deficiency zygotes survive to the late pupal stage. These zygotes have a deficiency for the wild type allele, therefore the normally recessive mutant allele wp could be expressed (pseudo-dominance).The overall fitness of the three lines was calculated, and their suitability for the genetic sexing of large populations is discussed.     

Superoxide production by polymorphonuclear leukocytes

Summary Phagocytosis by polymorphonuclear leukocytes triggers a burst of oxidative metabolism resulting in hydrogen peroxide and superoxide production, and these active oxygen species function in the killing of microorganisms. A new cytochemical technique, based on a manganese dependent diaminobenzidine oxidation, has been developed to detect superoxide in these cells. It has been shown that superoxide generation is associated with the plasma membrane in cells activated by particulate (zymosan) and nonparticulate (phorbol myristate acetate) stimuli. This membraned activity is maintained during invagination such that reduced oxygen is generated within the endocytic vacuoles. Reaction product is absent from unstimulated cells; additionally, formation of precipitate is blocked by omission of Mn⁺⁺, low temperature, glutaraldehyde prefixation, and the presence of superoxide dismutase in the incubation medium.In honour of Prof. P. van Duijn