INFLUENCE OF SUPPLEMENTAL INORGANIC NUTRIENTS ON GROWTH,SURVIVORSHIP, AND MYCORRHIZAL RELATIONSHIPS OF SCHIZACHYRIUM SCOPARIUM (POACEAE) GROWN IN FUMIGATED AND UNFUMIGATED SOIL

Little bluestem grass Schizachyrium scoparium ([Michx.] Nash) plants were grown under field conditions for 2 years in soils fumigated with methyl bromide and chloropicrin, or in unfumigated soil, and treated with supplemental inorganic nutrients (bases calcium and magnesium) phosphorus, nitrogen, and potassium. Most differences in measured plant responses were due to interactions between fumigation and nutrient treatments. These included biomass production, root mass per unit length (μg/cm), root lengths, flowering culm production, percent colonization, colonized root length, and spore production in rhizosphere soil. Plants generally responded to mycorrhizal fungal colonization by reducing total root length and producing thicker roots. Treatment of plants with bases appeared to profoundly affect the mycorrhizal association by reducing sporulation of vesicular-arbuscular mycorrhizal fungi and increasing colonization. When fumigated or unfumigated soils were considered separately, base-treated plants produced more biomass than other treatments. Base-treated plants grown on unfumigated soil had more flowering culms and longer colonized root lengths than all other plants. Percent colonization by mycorrhizal fungi and colonized root length were positively correlated with phosphorus/nitrogen ratios, but the ratio was not correlated with plant biomass production. This suggests that phosphorus is not a limiting nutrient in our soil and investment in a mycorrhizal association may not result in enhanced plant growth. The base-nutrient effects may indicate a need to reevaluate earlier studies of macro nutrient effects that did not take into account the role played by calcium and magnesium in assessing fungus-host plant interactions.     

Are the spatial patterns of weeds scale-invariant?

In previous empirical and modelling studies of rare species and weeds, evidence of fractal behaviour has been found. We propose that weeds in modern agricultural systems may be managed close to critical population dynamic thresholds, below which their rates of increase will be negative and where scale-invariance may be expected as a consequence. We collected detailed spatial data on five contrasting species over a period of three years in a primarily arable field. Counts in 20×20 cm contiguous quadrats, 225,000 in 1998 and 84,375 thereafter, could be re-structured into a wide range of larger quadrat sizes. These were analysed using three methods based on correlation sum, incidence and conditional incidence. We found non-trivial scale invariance for species occurring at low mean densities and where they were strongly aggregated. The fact that the scale-invariance was not found for widespread species occurring at higher densities suggests that the scaling in agricultural weed populations may, indeed, be related to critical phenomena.     

COMPLEMENTARY SEX DETERMINATION IN HYMENOPTERAN PARASITOIDS AND ITS IMPLICATIONS FOR BIOLOGICAL CONTROL

Abstract In haplodiploid Hymenoptera, unfertilized eggs produce haploid males while fertilized eggs lead to diploid females under most circumstances. Diploid males can also be produced from fertilization under a system of sex determination known as complementary sex determination (CSD). Under single-locus CSD, sex is determined by multiple alleles at a single sex locus. Individuals heterozygous at the sex locus are female while hemizygous and homozygous individuals develop as haploid and diploid males, respectively. In multiple-locus CSD, two or more loci, each with two or more alleles, determine sex. Diploid individuals are female if one or more sex loci are heterozygous, while a diploid is male only if homozygous at all sex loci. Diploid males are known to occur in 43 hymenopteran species and single-locus CSD has been demonstrated in 22 of these species. Diploid males are either developmentally inviable or sterile, so their production constitutes a genetic load. Because diploid male production is more likely under inbreeding, CSD is a form of inbreeding depression. It is crucial to preserve the diversity of sex alleles and reduce the loss of genetic variation in biological control. In the parasitoid species with single-locus CSD, certain precautionary procedures can prevent negative effects of single-locus CSD on biological control.     

Eccentric contractions require unique activation strategies by the nervous system

Enoka, Roger M. Eccentric contractions require uniqueactivation strategies by the nervous system. J. Appl.Physiol. 81(6): 2339-2346, 1996.Eccentriccontractions occur when activated muscles are forcibly lengthened. Thismode of muscle function occurs frequently in the activities of dailyliving and in athletic competition. This review examines theexperimental evidence that provides the foundation for our currentunderstanding of the benefits, consequences, and control of eccentriccontractions. Over the past several decades, numerous studies haveestablished that eccentric contractions can maximize the force exertedand the work performed by muscle; that they are associated with agreater mechanical efficiency; that they can attenuate the mechanicaleffects of impact forces; and that they enhance the tissue damageassociated with exercise. More recent evidence adds a new feature tothis repertoire by suggesting a new hypothesis: that the neuralcommands controlling eccentric contractions are unique. Examination of this hypothesis is critical because the existence of such a control scheme would increase substantially the complexity of the strategies that the nervous system must use to control movement.

     

Developmental regulation of aldoxime formation in seedlings and mature plants of Chinese cabbage (Brassica campestris ssp. pekinensis) and oilseed rape (Brassica napus): Glucosinolate and IAA biosynthetic enzymes

The first steps in the biosynthesis of glucosinolates and indole-3-acetic acid (IAA) in oilseed rape (Brassica napus L.) and Chinese cabbage (Brassica campestris ssp. pekinensis) involve the formation of aldoximes. In rape the formation of aldoximes from chain-extended amino acids, for aromatic and aliphatic glucosinolate biosynthesis, is catalysed by microsomal flavin-containing monooxygenases. The formation of indole-3-aldoxime from l-tryptophan, the potential precursor of both indole-3-acetic acid and indolyl-glucosinolates, is catalysed by several microsomal peroxidases. The biosynthesis of glucosinolates and indole-3-acetic acid was shown to be under developmental control in oilseed rape and Chinese cabbage. No monooxygenase activities were detected in cotyledons or old leaves of either species. The highest monooxygenase activities were found in young expanding leaves; as the leaves reached full expansion and matured the activities decreased rapidly. The indole-aldoxime-forming activity was found in all of the tissues analysed, but there was also a clear decrease in foliar activity with maturity in leaves of rape and Chinese cabbage. Partial characterisation of the Chinese cabbage monooxygenases showed that they have essentially identical properties to the previously characterised rape enzymes; they are not cytochrome P450-type enzymes, but resemble flavin-containing monooxygenases. No monooxygenase inhibitors were detected in microsomes prepared from either cotyledons or old leaves.Abbreviations DHMet dihomomethionine - FMO flavin-containing monooxygenase - HPhe homophenylalanine - IAA indole-3-acetic acid - l-Phe l-phenylalanine - l-Trp l-tryptophan - MO monooxygenase - IAALD indole-3-acetaldehyde - IAOX indole-3-aldoxime - THMet trihomomethionine     

Assessment of microinjection for introducing DNA into uninuclear microspores of rapeseed

Approximately 2,000 embryogenic uninuclear microspores of rapeseed (Brassica napus) cv. Topas were intranuclearly injected with a chimaeric -glucuronidase (Escherichia coli Uid A) gene. Stable integration had not occurred among 55 plants that were regenerated. Coinjection of the dye Lucifer Yellow and detection of injected DNA by the polymerase chain reaction revealed high frequencies of transfer. However, the amount of DNA injected was less than 20 copies, which may have been insufficient for stable transformation of microspores.Abbreviations PCR polymerase chain reaction - GUS -glucuronidase     

Inhibition of nitrous oxide reduction by a component of Hamilton Harbour sediment

Abstract: A component of Hamilton Harbour sediment prevented nitrous oxide (N₂O) reduction in denitrification assays with a mixed population of endogenous bacteria and a pure culture (HH1) isolated from the sediment. A 5% (v/v) concentration of sediment in nutrient broth caused near maximum inhibition of N₂O reduction. Sediment taken from a site closer to pollution sources (Site 906) was twice as inhibitory (as measured by N₂O accumulation) as sediment from Site 910, further from pollution sources. N₂O persistence was associated with the particulate sediment fraction only. Several heavy metals were tested at in situ concentrations, and ionic cadmium (Cd) and chromium (Cr) caused N₂O accumulation. Ashed sediment did not cause N₂O accumulation, but did decrease initial nitrate reduction rates with HH1.     

Evidence for selective effects of vanadium on adipose cell metabolism involving actions on cAMP-dependent protein kinase

The insulin-like effects of vanadiumin vivo are likely to be achieved at micromolar concentrations. Demonstrated effects of vanadium on adipose tissue of streptozotocin-diabetic rats include inhibition of basal and stimulated rates of lipolysis and effects on fat cell protein phosphorylation. The studies described below examined the effects of vanadium (to a maximum concentration of 0.5 mM) on adipose cells or tissuein vitro. Vanadium, added as a vanadyl-albumin complex or as sodium orthovanadate, produced a marked (greater than 50%) inhibition of isoproterenol-stimulated lipolysis. Inhibition of lipolysis equivalent to that seen with insulin, was achieved with 100 M vanadium. In contrast, no insulin-like stimulation ofde novo fatty acid biosynthesis was observed with vanadium below 0.5 mM. Surprisingly, the antilipolytic effects of vanadium persisted in the presence of cilostamide, an inhibitor of the insulin-sensitive isoform of cyclic nucleotide phosphodiesterase. Studies with purified preparations of the catalytic subunit of cyclic AMP-dependent protein kinase revealed dose-dependent inhibition with vanadyl-glutathione (to a maximum of 40% inhibition). Equivalent inhibition of cyclic AMP-dependent phosphorylation of Kemptide (50%) was observed upon incubation of freshly-prepared fat-pad supernatant fractions with vanadyl-glutathione. These results suggest that effects of low concentrations of vanadium may be mediated, at least in part, by actions on the catalytic subunit of cyclic AMP-dependent protein kinase.