Microbial communities colonising nutrient-enriched marine sediment

Sediment cores were set up to study microbial colonisation and interactions on marine sand grains under enrichment conditions. Cores were enriched with photosynthetic media in the light and dark (PL, PD) and heterotrophic media in the light and dark (HL, HD), and were incubated for 25 days. Sediment chlorophylls were then measured by acetone extraction, viable heterotrophic bacteria by plate counts, and numbers of cells mm^–2 sand grain surface by s.e.m. Chlorophyll a occurred in all sediments but was highest in the PL sediment. Bacteriochlorophyll a was only observed in the HL sediment. Heterotrophic viable counts were high in the HL and HD sediments. Dense growth of diatoms and blue-green algae, and a marine fungal Thraustochytrid sp. occurred on PL grains. The blue-green alga Schizothrix was often associated with the diatom Amphora on PL grains. Many different bacteria grew on HL and HD grains and some unusual colony and cell morphologies were recorded (Caulobacter, Flexibacter, polymer strands). Characteristic flakey material sometimes occurred in hollows on grains. The results are discussed in relation to microbial communities in low energy sedimentary environments.     

Helicotylenchus scoticus n.sp. and a conspectus of the genus Helicotylenchus Steiner, 1945 (Tylenchida: Nematoda)

Summary Helicotylenchus scoticus n. sp. is described. It was found at an altitude of 660 m on the north-west slope of Sgurr Cos na Breachd-laoidh, Scotland, in a rough grassland consisting predominantly of tufted hair grass (Deschampsia caespitosa). This species is characterized by a relatively long spear and an oesophagus which superficially appears to abut on to the intestine with virtually no overlap. The number of nominal species in the genus Helicotylenchus has increased considerably over recent years and stands now at 154 species. The task of identifying species in this genus using dichotomous keys has become increasingly more difficult. As a practical alternative a compendium is given which uses nine of the most diagnostic characters.     

Calcitonin- and somatostatin-positive cells in thyroid gland of pigs at different ages

Immunohistochemical studies were carried out on calcitonin-, somatostatin- and serotonin-reactive cells in newborn pigs and pigs at 3 weeks and 7 months old. The aim of these studies was to examine if the expression of various bioactive substances by parafollicular cells in the pig thyroid varied during development. The volume density of the follicular epithelium was nearly the same in newborn and 3-week-old piglets and significantly lower in 7-month-old animals. The volume density of calciton-in-positive cells, expressed as a percentage of the follicular epithelium density, was similar in young animals, being 12.10% and 13.03% in newborn and 3-week-old piglets, respectively. A small but significant increase to 14.40% was seen in 7-month-old pigs. Somatostatin-positive cells formed a much smaller population at all time points, but these also showed a significant increase with age (0.13%, 0.17% and 0.52% of follicular epithelium density in newborn, 3-week- and 7-month-old pigs, respectively). However the changes in the volume density of somatostatin-positive cells correlated inversely with thyroid activity, the density being highest when the activation index was lowest, suggesting that thyroid activity may be regulated by an increase in the synthesis of this inhibitory peptide. Serotonin-positive cells were extremely rare at all time points and their volume density was not calculated.     

Preparation and structural characterization of large heparin-derived oligosaccharides

Porcine mucosal heparin was partially depolymerized with heparinlyase I and then fractionated into low-molecularweight (<5000)and high-molecular-weight (>5000) oligosaccharides by pressurefiltration. The high-molecular-weight oligosaccharide mixture({small tilde}50 wt% of the starting heparin) also containedintact heparin. This intact polymer complicates oligosacsharidepurification. Thus, the low-molecular-weight fraction was usedto prepare homogeneous oligosaccharides for structural characterization.The low-molecular-weight oligosaccharide mixture was first fractionatedby low pressure gel permeation chromatography into size-uniformmixtures of disaccharides, tetrasaccharides, hexasaccharides,octasaccharides, decasaccharides, dodecasaccharides, tetradecasaccharidesand higher oligosaccharides. Each size-fractionated mixturewas then purified on the basis of charge by repetitive semi-preparativestrong-anion-exchange high-performance liquid chromatography.This approach has led to the isolation of 14 homogeneous oligosaccharidesfrom disaccharide to tetradecasaccharide. The purity of theseheparin-derived oligosaccharides was determined by gradientpolyacrylamide gel electrophoresis, analytical strong-anion-exchangehigh-performance liquid chromatography, capillary electrophoresisand one-dimensional nuclear resonance spectroscopy. The structureof these oligosaccharides was established using 600 MHz two-dimensionalnuclear resonance spectroscopy . The spectral methods used includedhomonuclear correlation spectroscopy, nuclear Overhauser effectspectroscopy and heteronuclear multiple quantum coherence spech-clscopy.The ¹H/¹H connectivities of the protons of each sugar residuein an oligosaccharide were established by two-dimensional homonuclearcorrelation spectroscopy, while ¹H/¹³C assignments were madeusing ¹H inverse detection. One- and two-dimensional nuclearresonance spectroscopic analysis of these heparin oligosaccharidesshowed two closely related groups of heparin-oligosaccharidesare afforded by enzymatic depolymerization of heparin. One groupis fully sulphated, having the structures     

Some studies on Tylenchorhynchinae: proposal ofDivittus n.g. (Nematoda: Tylenchida)

Summary A new genusDivittus is proposed in the subfamily Tylenchorhynchinae Eliava, 1964 with only three incisures in the non-areolated lateral fields and the body cuticle without longitudinal ridges or lamellae. It is also proposed to restrictTrilineellus Lewis & Golden, 1981 to its type species only, i.e.,T. clathrocutis which has three incisures in the lateral fields and longitudinal ridges or lamellae on the body, andTylenchorhynchus to species which have four incisures in the lateral fields but no ridges or lammellae.T. divittatus Siddiqi, 1961,T. triglyphus Seinhorst, 1963 andT. sculptus Seinhorst, 1963 which were transferred toTrilineellus by Lewis & Golden (1981) are now included inDivittus with the following species ofTylenchorhynchus which have three incisures in the lateral fields:T. obscurisulcatus Andrássy, 1959,T. chonai Sethi & Swarup, 1968,T. madrasensis Gupta & Uma, 1981 andT. pruni Gupta & Uma, 1981. The synonymy ofT. chonai withT. triglyphus proposed by Tarjan (1973) is not accepted.Divittus labiatus n.sp. from soil around roots of sugarcane from north-eastern Nigeria is described. It is characterized by having the lip region continuous with the body, the spear 14–16 m long, the basal oesophageal bulb with a small overlap over the intestine and the tail with a large post-anal intestinal sac and 20 to 30 annules. A key to species ofDivittus is provided. ac]19830105     

Variation in root morphology,enhancement in anti-oxidative enzyme responses and improved arbutin and bergenin levels in Bergenia ciliata (Haw.) Sternb. raised in vitro via EMS and gamma irradiations

Plant Cell, Tissue and Organ Culture (PCTOC) - Plant cells develop defence mechanisms in response to mutagen stress which leads to modulation of certain metabolic and defensive pathways. Owing to...     

Polymorphism in the internal transcribed spacer (ITS) region of the ribosomal DNA among different Fusarium species

Fusarium species causing wilt diseases in different plants were characterised by comparing nonpathogenic and different pathogenic species using rDNA RFLP analysis. The ITS (internal transcribed spacer) region of 12 isolates belonging to the section Elegans, Laseola, Mortiella, Discolor, Gibbosum, Lateritium and Sporotrichiella were amplified by universal ITS primers (ITS-1 and ITS-4) using polymerase chain reaction (PCR). Amplified products, which ranged from 522 to 565 bp were obtained from all 12 Fusarium isolates. The amplified products were digested with seven restriction enzymes, and restriction fragment length polymorphism (RFLP) patterns were analysed. A dendrogram derived from PCR-RFLP analysis of the rDNA region divided the Fusarium isolates into three major groups. Assessment of molecular variability based on rDNA RFLP clearly indicated that Fusarium species are heterogeneous and most of the forma speciales have close evolutionary relationships.     

Plant Life History and Residue Chemistry Influences Emissions of CO2 and N2O From Soil – Perspectives for Genetically Modified Cell Wall Mutants

Vascular plants have lignified tissues that transport water, minerals, and photosynthetic products throughout the plant. They are the dominant primary producers in terrestrial ecosystems and capture significant quantities of atmospheric carbon dioxide (CO₂) through photosynthesis. Some of the fixed CO₂ is respired by the plant directly, with additional CO₂ lost from rhizodeposits metabolized by root-associated soil microorganisms. Microbially-mediated mineralization of organic nitrogen (N) from plant byproducts (rhizodeposits, dead plant residues) followed by nitrification generates another greenhouse gas, nitrous oxide (N₂O). In anaerobic soils, reduction of nitrate by microbial denitrifiers also produces N₂O. The plant-microbial interactions that result in CO₂ and N₂O emissions from soil could be affected by genetic modification. Down-regulation of genes controlling lignin biosynthesis to achieve lower lignin concentration or a lower guaiacyl:syringyl (G:S) ratio in above-ground biomass is anticipated to produce forage crops with greater digestibility, improve short rotation woody crops for the wood-pulping industry and create second generation biofuel crops with low ligno-cellulosic content, but unharvested residues from such crops are expected to decompose quickly, potentially increasing CO₂ and N₂O emissions from soil. The objective of this review are the following: 1) to describe how plants influence CO₂ and N₂O emissions from soil during their life cycle; 2) to explain how plant residue chemistry affects its mineralization, contributing to CO₂ and N₂O emissions from soil; and 3) to show how modification of plant lignin biosynthesis could influence CO₂ and N₂O emissions from soil, based on experimental data from genetically modified cell wall mutants of Arabidopsis thaliana. Conceptual models of plants with modified lignin biosynthesis show how changes in phenology, morphology and biomass production alter the allocation of photosynthetic products and carbon (C) losses through rhizodeposition and respiration during their life cycle, and the chemical composition of plant residues. Feedbacks on the soil environment (mineral N concentration, soil moisture, microbial communities, aggregation) affecting CO₂ and N₂O emissions are described. Down-regulation of the Cinnamoyl CoA Reductase 1 (CCR1) gene is an excellent target for highly digestable forages and biofuel crops, but A. thaliana with this mutation has lower plant biomass and fertility, prolonged vegetative growth and plant residues that are more susceptible to biodegradation, leading to greater CO₂ and N₂O emissions from soil in the short term. The challenge in future crop breeding efforts will be to select tissue-specific genes for lignin biosynthesis that meet commercial demands without compromising soil CO₂ and N₂O emission goals.     

Morningness-eveningness preferences,learning approach and academic achievement of undergraduate medical students

ABSTRACT

Several studies have focused on determining the effect of chronotype and learning approach on academic achievement separately indicating that morning types have an academic advantage over the evening types and so have the deep learners over the surface learners. But, surprisingly none have assessed the possible relationship between chronotype and learning approach. So, the current study aimed to evaluate this association and their individual influence on academic performance as indicated by the Cumulative Grade Point Average (CGPA) as well as the effect of their interaction on academic performance. The study included 345 undergraduate medical students who responded to reduced Morningness-Eveningness Questionnaire and Biggs Revised Two-Factor Study Process Questionnaire. Morning types indulged in deep learning while evening types in surface learning. Morning and evening types did not differ on academic performance but deep learners had better academic outcomes than their counterparts. The interaction between chronotype and learning approach was significant on determining academic achievement. Our findings gave the impression that chronotype could have an impact on academic performance not directly but indirectly through learning approaches.