EFFECTS OF HUMAN ACTIVITIES ON STRUCTURE AND COMPOSITION OF WOODY SPECIES OF THE NOKREK BIOSPHERE RESERVE OF MEGHALAYA,NORTHEAST INDIA

Aims Our study was conducted in the Nokrek Biosphere Reserve (NBR) in the Garo hills districts of Meghalaya, Northeast India. Our aim was to assess the effects of human activities on plant diversity,population structure and regeneration.Methods We selected a representative 1.2 hm2 stand in both the core and buffer zones of NBR. Structure and composition were determined by randomly sampling square quadrats, population structure was assessed by determining age structure, and regeneration was assessed by measuring densities of seedling, sapling and adult trees.Important findings More woody species were recorded from the core zone than the buffer zone (87 vs. 81 species), and there were a large number of tropical, temperate, and Sino-Himalayan, Burma-Malaysian and Malayan elements, primitive families and primitive genera. The trees were distributed in three distinct strata,canopy, subcanopy and sapling. Subcanopy and sapling layers had the highest species richness (81％ -88％ ). Lauraceae and Euphorbiaceae were the dominant families in terms of the number of species, and a large number of families were represented by single species. Most woody species (57 ％ - 79 ％ ) were contagiously distributed and had low frequency ( ＜ 20％ ). Although stand density was high in the buffer zone, its basal area was low compared to the stand in the core zone. Low similarity and high β-diversity indicate marked differences in species composition of the stands. Shannon diversity index was high in both the stands, while Simpson dominance index was low. The diameter-class distribution for dominant species revealed that the most had a large number of young individuals in their populations. Preponderance of tree seedlings, followed by a steep decline in population density of saplings and adult trees, indicated that the seedling to sapling stage was the most critical in the life cycle of the tree populations. Most species (42 ％ - 48 ％ ) had no regeneration,25 ％ - 35 ％ had good/fair regeneration, and the rest had poor regeneration or reoccurred as immigrants.     

The N-terminal third of the BinB subunit from the Bacillus sphaericus binary toxin is sufficient for its interaction with midgut receptors in Culex quinquefasciatus

Heterodimeric binary (Bin) toxin, the major insecticidal protein from Bacillus sphaericus, acts on Culex quinquefasciatus larvae through specific binding to the midgut receptor Cqm1, a role mediated by its 448-amino-acid-long BinB subunit. The molecular basis for receptor recognition is not well understood and this study attempted to identify protein segments and amino acid motifs within BinB that are required for this event. First, N- and C-terminally truncated constructs were evaluated for their capacity to bind to native Cqm1 through pull-down assays. These showed that residues N33 to L158 of the subunit are required for Cqm1 binding. Nine different full-length mutants were then generated in which selected blocks of three amino acids were replaced by alanines. In new pull-down assays, two mutants, in which residues (85) IRF(87) and (147) FQF(149) were targeted, failed to bind the receptor. Competition binding assays confirmed the requirements for the N-terminal 158 residues, and the (147) FQF(149) epitope, for the mutant proteins to compete with native Bin toxin when binding to membrane fractions from the insect midgut. The data from this work rule out the involvement of C-terminal segments in receptor binding, highlighting the need for multiple elements within the protein's N-terminal third for it to occur.     

Lipid Auxotrophy and the Effect on Lipid Composition of Entamoeba invadens*†

SYNOPSIS. A medium for the axenic cultivation of Entamoeba invadens has been developed. Serum, an essential constituent of conventional media, has been replaced by a mixture of albumin, unsaturated fatty acids, Tween, and cholesterol to control the lipid composition of the medium. Entamoeba invadens requires both cholesterol and unsaturated fatty acids for growth. The fatty acid composition of the phospholipids of the ameba reflects that of the medium to a great extent, especially with regard to the unsaturated fatty acids. The amount of membrane bounded cholesterol depends on the cholesterol concentration in the medium.     

Liver cytochrome P-450 system in rats with a varying susceptibility to the development of experimental alcoholism

The cytochrome P-450-dependent monooxygenase system of the liver was studied in laboratory noninbred male rats selected according to the intensity of their initial alcohol motivation and the dynamics of these parameters was followed up during 10-day alcoholisation. It was shown that in the animals inclined to the development of alcoholism the activity of the monooxygenase system (cytochrome P-450, B5; enzymes: aminopyrine N-demethylase, aniline p-hydroxylase, NADPH-cytochrome c-reductase) is higher than in the animals noninclined to the development of this disease. 10-day alcohol consumption in the free-choice situation between water and 15% ethanol solution did not change the parameters investigated. The only exception was NADPH-cytochrome c-reductase: its activity grew in both the groups of the animals by 40-75%.     

Detection of an Allele Conferring Resistance to Bacillus sphaericus Binary Toxin in Culex quinquefasciatus Populations by Molecular Screening

The activity of the Bacillus sphaericus binary (Bin) toxin on Culex quinquefasciatus larvae depends on its specific binding to the Cqm1 receptor, a midgut membrane-bound α-glucosidase. A 19-nucleotide deletion in the cqm1 gene (cqm1_REC) mediates high-level resistance to Bin toxin. Here, resistance in nontreated and B. sphaericus-treated field populations of C. quinquefasciatus was assessed through bioassays as well as a specific PCR assay designed to detect the cqm1_REC allele in individual larvae. Resistance ratios at 90% lethal concentration, gathered through bioassays, were close to 1 and indicate that the selected populations had similar levels of susceptibility to B. sphaericus, comparable to that of a laboratory colony. A diagnostic PCR assay detected the cqm1_REC allele in all populations investigated, and its frequency in two nontreated areas was 0.006 and 0.003, while the frequency in the B. sphaericus-treated population was significantly higher. Values of 0.053 and 0.055 were detected for two distinct sets of samples, and homozygote resistant larvae were found. Evaluation of Cqm1 expression in individual larvae through α-glucosidase assays corroborated the allelic frequency revealed by PCR. The data from this study indicate that the cqm1_REC allele was present at a detectable frequency in nontreated populations, while the higher frequency in samples from the treated area is, perhaps, correlated with the exposure to B. sphaericus. This is the first report of the molecular detection of a biolarvicide resistance allele in mosquito populations, and it confirms that the PCR-based approach is suitable to track such alleles in target populations.     

The chemical synthesis of glucosaminylphosphatidylglycerol. Comparison with a new phospholipid isolated from Bacillus megaterium

1. We describe the synthesis of a glucosamine derivative of phosphatidylglycerol having the same structure as that of the natural compound isolated from Bacillus megaterium. 2. 2-O-(3,4,6-Tri-O-acetyl-2-deoxy-2-phthalimido-d-glucopyranosyl)-3-O-benzyl-1-iodo-sn-glycerol was prepared by a Königs–Knorr condensation between 3-O-benzyl-1-toluene-p-sulphonyl-sn-glycerol and 3,4,6-tri-O-acetyl-1-bromo-2-deoxy-2-phthalimido-d-glucopyranose followed by replacement of the toluene-p-sulphonyl group with iodine. The iodide was treated with the silver salt of 2-isolauroyl-1-oleoyl-sn-glycerol 3-(monobenzyl hydrogen phosphate) to form the fully protected phosphoglycolipid. 3. Removal of benzyl protecting groups by catalytic hydrogenolysis, phthaloyl group with hydrazine and acetyl groups with pH10 buffer furnished 2-O-(2-amino-2-deoxy-d-glucopyranosyl)-1-(2-isolauroyl-1-stearoyl-sn-glycero-3-phosphoryl)-sn-glycerol. 4. The synthetic and natural compounds appeared identical when compared by chromatography and by identification of hydrolysis products from chemical and enzymic degradations.     

A second independent resistance mechanism to Bacillus sphaericus binary toxin targets its alpha-glucosidase receptor in Culex quinquefasciatus

The entomopathogen Bacillus sphaericus is an important tool for the vector control of Culex sp., and its effectiveness has been validated in field trials. The appearance of resistance to this bacterium, however, remains a threat to its use, and attempts have been made to understand the resistance mechanisms. Previous work showed that the resistance to B. sphaericus in a Culex quinquefasciatus colony is associated with the absence of the approximately 60-kDa binary toxin receptor in larvae midgut microvilli. Here, the gene encoding the C. quinquefasciatus toxin receptor, Cqm1, was cloned and sequenced from a susceptible colony. The deduced amino-acid sequence confirmed its identity as an alpha-glucosidase, and analysis of the corresponding gene sequence from resistant larvae implicated a 19-nucleotide deletion as the basis for resistance. This deletion changes the ORF and originates a premature stop codon, which prevents the synthesis of the full-length Cqm1. Expression of the truncated protein, however, was not detected when whole larvae extracts were probed with antibodies raised against an N-terminal 45-kDa recombinant fragment of Cqm1. It seems that the premature stop codon directs the mutated cqm1 to the nonsense-mediated decay pathway of mRNA degradation. In-gel assays confirmed that a single alpha-glucosidase protein is missing from the resistant colony. Further in vitro affinity assays showed that the recombinant fragment binds to the toxin, and mapped the binding site to the N-terminus of the receptor.     

Biogeochemical interactions between iron and sulphate in freshwater wetlands and their implications for interspecific competition between aquatic macrophytes

1. Wetlands are threatened by desiccation, eutrophication and changing water quality, generally leading to greatly altered biogeochemical processes. Sulphate pollution can lead to severe eutrophication and sulphide toxicity, but may also interact with the availability of iron and other metals. 2. In the present study, we examined the biogeochemical interactions between sulphate and iron availability, and their effects on aquatic macrophytes, in a field experiment with enclosures. The natural iron supply by groundwater was mimicked by adding iron to the sediment, and the effect of increased sulphate concentrations in the surface water was also studied. The enclosure experiment was performed in a mesotrophic, anaerobic ditch in a peat meadow reserve in the Netherlands. In all enclosures, three Stratiotes aloides plants were introduced to serve as indicator species. 3. Addition of sulphate led to the mobilisation of phosphate, whereas addition of iron or both iron and sulphate did not affect P mobilisation. Growth of S. aloides was decreased by both iron addition and sulphate addition (sulphide toxicity). Addition of iron under sulphidic conditions, however, led to mutual detoxification of both toxicants (iron and sulphide) and did not decrease S. aloides growth. The uptake of metals was highest in the treatment involving sulphate addition, probably as a result of increased mineralisation of the peat soil. 4. Growth of Elodea nuttallii, which grew naturally in the enclosures, was stimulated by iron or iron plus sulphate addition. It did not, however, grow in the enclosures with sulphate addition, as a result of sulphide toxicity or sulphide‐induced iron deficiency. Under iron‐rich conditions, E. nuttallii appeared to be a better competitor than S. aloides and depressed the growth of the latter species. 5. We propose that the growth of S. aloides is directly regulated by interactions between sulphide and iron and indirectly by the effects of both compounds on the competitive strength of E. nuttallii. In general, we conclude that biogeochemical interactions between sulphate and iron can have a strong influence on plant species composition in freshwater wetlands, because of direct effects or changes in the competitive strength of plant species related to differential sensitivity to either iron or sulphide.