Fungal spore concentrations in the air at Tiruchirapalli (India) 1987–1988

Summary Using an aeroscope, airborne fungal spores were sampled for two years, 1987–1988 at Tiruchirapalli, Tamil Nadu, India. The aerospora components, their seasonal and annual variations in incidence in the air are discussed and a spore calendar for Tiruchirapalli is presented.     

Infectivity,viability and effects of Paranosema locustae (Microsporidia) on juveniles of Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) under laboratory conditions

Infectivity and effects on host of a long-term stored aqueous suspension of Paranosema locustae on juveniles of Dichroplus maculipennis, a pest grasshopper in parts of the Pampas and Patagonia, were evaluated. Infections developed in 90–97.8% of treated individuals. Mortality increased with time, reaching highest values at 30–40 days post-inoculation (79.5–100%). Infected nymphs showed significantly slower development.     

Sperm cell surface characteristics of Plumbago zeylanica L. in relation to transport in the embryo sac

Myosin associated with the male germ cells of angiosperms interacts with actin, promoting transport of the non-motile generative and later sperm cells in the pollen tube. Myosin localizing on the sperm cell plasma membrane seems negligible in Plumbago, as reflected by the absence of: (i) anti-myosin labeling using immunoelectron microscopy, (ii) sperm motility on actin matrices, and (iii) electrophoretic movement changes after addition of antibody. Sperm cells injected directly into actively streaming Nitella internodal cells, however, follow actin bundles and their movement is sensitive to ATP and Mg²⁺. This may be based on simple charge binding since negatively charged latex beads also migrate on actin, whereas neutral or positively-charged latex beads do not. Sperm cells are negatively charged according to capillary microelectrophoresis, whereas killed sperm cells, which are positively charged do not migrate. The sperm cell that normally fertilizes the egg has a higher calculated charge (8.277 × 10³ esu/cm²) compared with the sperm cell that fuses with the central cell (6.120 × 10³ esu/cm²). Received: 15 December 1998 / Accepted: 21 January 1999     

Somatic and Dendritic Encoding of Spatial Variables in Retrosplenial Cortex Differs during 2D Navigation

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Nitrogen Oxyanion-dependent Dissociation of a Two-component Complex That Regulates Bacterial Nitrate Assimilation

Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression.     

The potential utility of postnatalskeletal developmental patterns in squamate phylogenetics

Postnatal patterns of skeletal development, includingthe sequence of appearance of ossification centres and the distributionof sesamoids, appear to be highly conserved species-level phenomenain squamates. As such, they are a potential source of charactersfor phylogenetic inquiry. These patterns, from 21 species representing14 crown squamate clades, form the basis for two analyses. In thefirst, the sequence of postnatal skeletal events is coded as charactersusing the sequence unit approach. This analysis reveals that thesequence of postnatal skeletal events might be useful for determiningrelationships at or above the level of crown clades, but not amongthem. The second analysis utilizes discrete data from postnatalskeletal development, such as the presence/absence of sesamoidsand the number of secondary centres in epiphyseal cartilages. Thesediscrete data appear capable of recovering the deeper divergenceswithin Squamata, but evolve too slowly to be informative at thelevel of crown clades. Thus, patterns of postnatal skeletal developmenthave the potential to help illuminate relationships throughout thesquamate tree. Further progress in this area will require the examinationof additional squamate species, the exploration of alternative codingschemes for developmental sequences, and comparable postnatal datafor Sphenodon .  © 2002 The Linnean Societyof London, Zoological Journal of the Linnean Society, 2002, 136 ,277−313.     

Standard dimensions forcis N-methyl peptide unit and flexibility ofcis peptide units

The mean dimensions of thecis N-methyl peptide unit have been arrived at by analysing the crystal structure data on compounds containing such units. These dimensions can be used as standard in conformational studies on cyclic peptides. While the bonds meeting at C are almost coplanar, those meeting at N show a slight pyramidal disposition. A comparison of the dimensions of the normal and N-methylatedcis peptide units show that there are perceptible differences in the parameters connected with N. In addition, the flexibility of thecis peptide unit has been analysed by studying the distribution of the parameters in different classes of compounds such as cyclic di, tri and higher peptides. The salient features are: (i) The angle C^αCN in cyclic dipeptide and the angle C^δNC^α in higher peptides tend to be lower, when the peptide unit is associated with a prolyl residue; (ii) in cyclic tripeptides the internal anglesviz., C^αCN and CNC^α are significantly larger thereby increasing the intra-annular space; (iii) the bond C^α-C is distinctly shorter when it occurs in cyclic dipeptides. The results lead to the conclusion that thecis peptide unit takes up aneed-based flexibility in its dimension.     

Environmental factors influencing the occurrence of juvenile fish in the mangroves of Pagbilao,Philippines

128 fish species belonging to 54 families were collected from the mangroves of Pagbilao. Ambassis kopsi (Ambassidae) was the most abundant species.Fourteen environmental factors were correlated to the catch per unit time for some species. The occurrence of A. kopsi was positively correlated to nitrate in the water, carbon in the sediments and litter fall. Out of the 8 species investigated, 6 were positively correlated to litter fall. Three species showed positive correlation to phosphate in the water, two to organic carbon in the sediments, nitrate, silicate and pH, and one to salinity and carotenoids in water. The biomass of the total catch was correlated to carbon in the sediments and litter fall.