Density‐dependence in common tree species in a tropical dry forest in Mudumalai,southern India

Abstract. Density‐dependence in tree population dynamics has seldom been examined in dry tropical forests. Using long‐term data from a large permanent plot, this study examined 16 common species in a dry tropical forest in southern India for density‐dependence. Employing quadrat‐based analyses, correlations of mortality, recruitment and population change with tree densities were examined. Mortality in 1–10 cm diameter trees was largely negatively correlated with conspecific density, whereas mortality in > 10 cm diameter trees was positively correlated. Mortality was, however, largely unaffected by the basal area and abundance of heterospecific trees. Recruitment was poor in most species, but in Lagerstroemia microcarpa (Lythraceae), Tectona grandis (Verbenaceae) and Cassia fistula (Fabaceae), species that recruited well, strong negative correlations of recruitment with conspecific basal area and abundance were found. In a few other species that could be tested, recruitment was again negatively correlated with conspecific density. In Lagerstroemia, recruitment was positively correlated with the basal area and abundance of heterospecific trees, but these correlations were non‐significant in other species. Similarly, although the rates of population change were negatively correlated with conspecific density they were positive when dry‐season ground fires occurred in the plot. Thus, the observed positive density‐dependence in large‐tree mortality and the negative density‐dependence in recruitment in many species were such that could potentially regulate tree populations. However, repeated fires influenced density‐dependence in the rates of population change in a way that could promote a few common species in the tree community.     

Leaf flushing phenology and herbivory in a tropical dry deciduous forest,southern India

Patterns of leaf-flushing phenology of trees in relation to insect herbivore damage were studied at two sites in a seasonal tropical dry forest in Mudumalai, southern India, from April 1988 to August 1990. At both sites the trees began to flush leaves during the dry season, reaching a peak leaf-flushing phase before the onset of rains. Herbivorous insects emerged with the rains and attained a peak biomass during the wet months. Trees that flushed leaves later in the season suffered significantly higher damage by insects compared to those that flushed early or in synchrony during the peak flushing phase. Species whose leaves were endowed with physical defenses such as waxes suffered less damage than those not possessing such defenses. There was a positive association between the abundance of a species and leaf damage levels. These observations indicate that herbivory may have played a major role in moulding leaf flushing phenology in trees of the seasonal tropics.     

Serotonin Modulates Nicotinic Responses of Adrenal Chromaffin Cells

Abstract: 5-Hydroxytryptamine (5-HT) specifically and reversibly inhibits nicotine-induced currents and catecholamine release in bovine adrenal chromaffin cells in culture. Pharmacological analysis indicates that the inhibition is not mediated by known 5-HT receptor subtypes. The inhibition is noncompetitive over a range of nicotine concentrations between 1 and 100 μM. Preincubation with either 5-HT or substance P significantly protects the response from nicotine-induced desensitization. It is concluded that 5-HT inhibits nicotinic acetylcholine receptors on bovine adrenal chromaffin cells, probably by binding to a noncompetitive site on the receptor itself. Because both blood and the chromaffin cells contain 5-HT, the inhibition provides an opportunity for negative control of catecholamine secretion from the adrenals.     

A specific vaccine effective against stage I and stage II malignant disease in guinea pigs effect of variations in preparations and storage

Summary Guinea pigs, each with an established, syngeneic dermal line 10 tumor and lymph node metastases, were immunized by intradermal injection of a mixture of irradiated line 10 cells and an emulsion containing heat-killed BCG. Immunization eradicated 7- or 10-day-old dermal tumors (about 10 or 12 mm in diameter, respectively) and prevented growth of microscopic lymph node metastases. Fourteen-day-old dermal tumors (about 15 mm in diameter) were not rejected by immunization.Guinea pigs with stage II disease (21-day-old dermal tumors and palpable metastases in the first draining lymph node) were treated by excision of the dermal tumor and the first draining lymph node, and by specific immunization. This treatment eliminated tumor cells remaining in the second draining lymph nodes. The surgical treatment alone was not curative, palpable metastases in the second draining lymph nodes progressed and the animals died (some with visible lung metastases).Emulsions containing killed BCG were good adjuvants even after prolonged storage at 4° C, but lost most of their adjuvant activity after autoclaving or freezing.     

The characterization of a sodium-dependent high affinity choline uptake system unassociated with acetylcholine biosynthesis

The cardiac ganglion of the horseshoe crab, Limulus polyphemus, was incubated in Chao's solution containing 0.01 microM [3H]choline at room temperature (25 +/- 2 degrees C) and the ganglion readily accumulated the radiolabel. The ganglion uptake of [3H]choline was linear over 60 min. Kinetic analysis revealed dual choline uptake systems within the cardiac ganglion, a high affinity uptake system (Km = 2.2 microM, Vmax = 0.16 pmoles/mg/min) and a low affinity system (Km = 92.3 microM, Vmax = 3.08 pmoles/mg/min). The high affinity uptake system was sodium-dependent and inhibited by micromolar concentrations of hemicholinium-3. A 15 min pre-exposure of the ganglion to Chao's solution containing 90 mM potassium stimulated a significant increase in choline uptake. There was no detectable synthesis of [3H]acetylcholine from the [3H]choline taken up by the cardiac ganglion. The major portion of the extractable label appeared in a fraction which co-electrophoresed with phosphorylcholine. These results suggest that the sodium-dependent high affinity [3H]choline uptake system of the cardiac ganglion subserves a specific requirement for choline which is unrelated to a cholinergic function.     

Sphingosine kinase 1 is required for migration, proliferation and survival of MCF-7 human breast cancer cells

Sphingosine-1-phosphate (S1P) is a potent lysolipid involved in a variety of biological responses important for cancer progression. Therefore, we investigated the role of sphingosine kinase type 1 (SphK1), the enzyme that makes S1P, in the motility, growth, and chemoresistance of MCF-7 breast cancer cells. Epidermal growth factor (EGF), an important growth factor for breast cancer progression, activated and translocated SphK1 to plasma membrane. SphK1 was required for EGF-directed motility. Downregulation of SphK1 in MCF-7 cells reduced EGF- and serum-stimulated growth and enhanced sensitivity to doxorubicin, a potent chemotherapeutic agent. These results suggest that SphK1 may be critical for growth, metastasis and chemoresistance of human breast cancers.     

Characterization of the disulfide bonds and free cysteine residues of the Chlamydia trachomatis mouse pneumonitis major outer membrane protein

Members of the genus Chlamydia lack a peptidoglycan layer. As a substitute for peptidoglycan, it has been proposed that several cysteine rich proteins, including the major outer membrane protein (MOMP), form disulfide bonds to provide rigidity to the cell wall. Alignment of the amino acids sequences of the MOMP from various serovars of Chlamydia showed that they have from 7 to 10 cysteine residues and seven of them are highly conserved. Which of these are free cysteine residues and which are involved in disulfide bonds is unknown. The complexity of the outer membrane of Chlamydia precludes at this point the characterization of the structure of the cysteines directly in the bacteria. Therefore, mass spectrometric analysis of a purified and refolded MOMP was used in this study. Characterization of the structure of this preparation of the MOMP is critical because it has been shown, in an animal model, to be a very effective vaccine against respiratory and genital infections. Here, we demonstrated that in this MOMP preparation four cysteines are involved in disulfide bonds, with intramolecular pairs formed between Cys(48) and Cys(55) and between Cys(201) and Cys(203). A stepwise alkylation, reduction, alkylation process using two different alkylating reagents was required to establish the Cys(48)-Cys(55) disulfide pair. The other residues in MOMP, Cys(51), Cys(136), Cys(226), and Cys(351), are free cysteines and could potentially form disulfide-linked complexes with other MOMP or other membrane proteins.     

Reduction of all-trans retinal to all-trans retinol in the outer segments of frog and mouse rod photoreceptors

The first step in the Visual Cycle, the series of reactions that regenerate the vertebrate visual pigment rhodopsin, is the reduction of all-trans retinal to all-trans retinol, a reaction that requires NADPH. We have used the fluorescence of all-trans retinol to study this reduction in living rod photoreceptors. After the bleaching of rhodopsin, fluorescence (excitation, 360 nm; emission, 457 or 540 nm) appears in frog and wild-type mouse rod outer segments reaching a maximum in 30-60 min at room temperature. With this excitation and emission, the mitochondrial-rich ellipsoid region of the cells shows strong fluorescence as well. Fluorescence measurements at different emission wavelengths establish that the outer segment and ellipsoid signals originate from all-trans retinol and reduced pyridine nucleotides, respectively. Using outer segment fluorescence as a measure of all-trans retinol formation, we find that in frog rod photoreceptors the NADPH necessary for the reduction of all-trans retinal can be supplied by both cytoplasmic and mitochondrial metabolic pathways. Inhibition of the reduction reaction, either by retinoic acid or through suppression of metabolic activity, reduced the formation of retinol. Finally, there are no significant fluorescence changes after bleaching in the rod outer segments of Rpe65(-/-) mice, which lack 11-cis retinal.     

Characterization of backcross introgression lines derived from <Emphasis Type="Italic">Oryza nivara</Emphasis> accessions for photosynthesis and yield

Improvement of photosynthetic traits is a promising strategy to break the yield potential barrier of major food crops. Leaf photosynthetic traits were evaluated in a set of high yielding Oryza sativa, cv. Swarna?×?Oryza nivara backcross introgression lines (BILs) along with recurrent parent Swarna, both in wet (Kharif) and dry (Rabi) seasons in normal irrigated field conditions. Net photosynthesis (P_N) ranged from 15.37 to 23.25 µmol (CO₂) m^?2 s^?1 in the BILs. Significant difference in P_N was observed across the seasons and genotypes. Six BILs showed high photosynthesis compared with recurrent parent in both seasons. Chlorophyll content showed minimum variation across the seasons for any specific BIL but significant variation was observed among BILs. Significant positive association between photosynthetic traits and yield traits was observed, but this association was not consistent across seasons mainly due to contrasting weather parameters in both seasons. BILs 166s and 248s with high and consistent photosynthetic rate exhibited stable high yield levels in both the seasons compared to the recurrent parent Swarna. There is scope to exploit photosynthetic efficiency of wild and weedy rice to identify genes for improvement of photosynthetic rate in cultivars.