Sphingosine-1-phosphate plays a role in the suppression of lateral pseudopod formation during Dictyostelium discoideum cell migration and chemotaxis

Sphingosine-1-phosphate (S-1-P) is a bioactive lipid that plays a role in diverse biological processes. It functions both as an extracellular ligand through a family of high-affinity G-protein-coupled receptors, and intracellularly as a second messenger. A growing body of evidence has implicated S-1-P in controlling cell movement and chemotaxis in cultured mammalian cells. Mutant D. discoideum cells, in which the gene encoding the S-1-P lyase had been specifically disrupted by homologous recombination, previously were shown to be defective in pseudopod formation, suggesting that a resulting defect might exist in motility and/or chemotaxis. To test this prediction, we analyzed the behavior of mutant cells in buffer, and in both spatial and temporal gradients of the chemoattractant cAMP, using computer-assisted 2-D and 3-D motion analysis systems. Under all conditions, S-1-P lyase null mutants were unable to suppress lateral pseudopod formation like wild-type control cells. This resulted in a reduction in velocity in buffer and spatial gradients of cAMP. Mutant cells exhibited positive chemotaxis in spatial gradients of cAMP, but did so with lowered efficiency, again because of their inability to suppress lateral pseudopod formation. Mutant cells responded normally to simulated temporal waves of cAMP but mimicked the temporal dynamics of natural chemotactic waves. The effect must be intracellular since no homologs of the S-1-P receptors have been identified in the Dictyostelium genome. The defects in the S-1-P lyase null mutants were similar to those seen in mutants lacking the genes for myosin IA, myosin IB, and clathrin, indicating that S-1-P signaling may play a role in modulating the activity or organization of these cytoskeletal elements in the regulation of lateral pseudopod formation.     

Effects of salt on growth,ion accumulation,photosynthesis and leaf anatomy of the mangrove,<Emphasis Type="Italic"> Bruguiera parviflora</Emphasis>

The effects of a range of salinity (0, 100, 200 and 400 mM NaCl) on growth, ion accumulation, photosynthesis and anatomical changes of leaves were studied in the mangrove, Bruguiera parviflora of the family Rhizophoraceae under hydroponically cultured conditions. The growth rates measured in terms of plant height, fresh and dry weight and leaf area were maximal in culture treated with 100 mM NaCl and decreased at higher concentrations. A significant increase of Na⁺ content of leaves from 46.01 mmol m^-2 in the absence of NaCl to 140.55 mmol m^-2 in plants treated with 400 mM NaCl was recorded. The corresponding Cl^- contents were 26.92 mmol m^-2 and 97.89 mmol m^-2. There was no significant alteration of the endogenous level of K⁺ and Fe²⁺ in leaves. A drop of Ca²⁺ and Mg²⁺ content of leaves upon salt accumulation suggests increasing membrane stability and decreased chlorophyll content respectively. Total chlorophyll content decreased from 83.44 g cm^-2 in untreated plants to 46.56 g cm^-2 in plants treated with 400 mM NaCl, suggesting that NaCl has a limiting effect on photochemistry that ultimately affects photosynthesis by inhibiting chlorophyll synthesis (ca. 50% loss in chlorophyll). Light-saturated rates of photosynthesis decreased by 22% in plants treated with 400 mM NaCl compared with untreated plants. Both mesophyll and stomatal conductance by CO₂ diffusion decreased linearly in leaves with increasing salt concentration. Stomatal and mesophyll conductance decreased by 49% and 52% respectively after 45 days in 400 mM NaCl compared with conductance in the absence of NaCl. Scanning electron microscope study revealed a decreased stomatal pore area (63%) in plants treated with 400 mM NaCl compared with untreated plants, which might be responsible for decreased stomatal conductance. Epidermal and mesophyll thickness and intercellular spaces decreased significantly in leaves after treatment with 400 mM NaCl compared with untreated leaves. These changes in mesophyll anatomy might have accounted for the decreased mesophyll conductance. We conclude that high salinity reduces photosynthesis in leaves of B. parviflora, primarily by reducing diffusion of CO₂ to the chloroplast, both by stomatal closure and by changes in mesophyll structure, which decreased the conductance to CO₂ within the leaf, as well as by affecting the photochemistry of the leaves.     

Genome relationship among nine species of Millettieae (Leguminosae: Papilionoideae) based on random amplified polymorphic DNA (RAPD)

Random amplified polymorphic DNA (RAPD) marker was used to establish intergeneric classification and phylogeny of the tribe Millettieae sensu Geesink (1984) (Leguminosae: Papilionoideae) and to assess genetic relationship between 9 constituent species belonging to 5 traditionally recognized genera under the tribe. DNA from pooled leaf samples was isolated and RAPD analysis performed using 25 decamer primers. The genetic similarities were derived from the dendrogram constructed by the pooled RAPD data using a similarity index, which supported clear grouping of species under their respective genera, inter- and intra-generic classification and phylogeny and also merger of Pongamia with Millettia. Elevation of Tephrosia purpurea var. pumila to the rank of a species (T. pumila) based on morphological characteristics is also supported through this study of molecular markers.     

The effect of duration and time of food availability on the photoperiodic response in the male house sparrow, Passer domesticus

We investigated the effects of food availability on the seasonal testicular growth in the photoperiodic house sparrow (Passer domesticus). Two experiments were performed, each lasting 4 weeks. In experiment 1, sparrows were exposed to natural (NDL; group 1), short (8L:16D; group 2) and long (16L:8D; groups 3-5) day lengths with access to food ad libitum (groups 1-3) or for 10 h (zeitgeber time (zt) 0-10, group 4; zt 0 is the time of light onset) or for 8 h (zt 8-16, group 5). Testes recrudesced under long, but not short and natural, day lengths, and the recrudescence under long days was influenced by the duration of food availability. In experiment 2, the sparrows were exposed to short (8L:16D, group 1) and long (16L:8D, groups 2-5) day lengths with access to food ad libitum (for groups 1 and 2) or for 6 h (for groups 3-5) at different times during the 16 h light period (group 3- zt 0-6, group 4- zt 5-11, group 5- zt 10-16). As the expected, the testes recrudesced only under long lengths, but the photoinduction was variable among the 4 groups. The testes grew to full size in groups 2 and 3 that received food either ad libitum or for 6 h at zt 0-6, but to sub-maximal size in the groups that received 6 h food either at zt 5-11 (group 4) or at zt 10-16 (group 5). Altogether, these results support the idea that the photoperiodic regulation of reproduction in a seasonally breeding species is influenced both by the duration and the time of food availability.     

Gene expression profiles in dendritic cells conditioned by 1alpha,25-dihydroxyvitamin D3 analog

Inhibition of dendritic cell (DC) maturity is an important immunomodulatory effect of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) and related analogs (D(3) analogs). The mechanisms underlying 1alpha,25(OH)(2)D(3)-mediated DC modulation are Vitamin D receptor (VDR)-dependent and likely involve direct or indirect regulation of multiple genes. Gene expression profiles of bone marrow-derived DCs (BMDCs) generated in the absence or presence of a potent D(3) analog were analyzed using microarray technology. Results for D(3) analog-conditioned DCs were also compared with glucocorticoid-conditioned BMDCs and with BMDCs conditioned with D(3) analog and glucocorticoid combined. Of approximately 12,000 gene products assayed, 52% were considered to have detectable expression in unconditioned BMDCs. Based on relative expression levels, 5.3% of these expressed genes were "silenced" or "suppressed" in D(3) analog-conditioned BMDCs and 2.1% were "augmented". In addition, 1.7% of gene products undetectable in control BMDCs were "induced" by D(3) analog. Functional grouping of modulated genes demonstrated important effects of D(3) analog on immunoreceptors, on chemokines and chemokine receptors, on growth factors/cytokines and related receptors, and on neuroendocrine hormones and related receptors. Many of these gene products were unaffected or differently regulated by glucocorticoid suggesting specific VDR-mediated regulatory effects. Confirmation of microarray analysis results for two differentially regulated chemokines (MIP-1alpha and RANTES) was obtained by RT-PCR and ELISA. The methodology provides novel insights into DC gene regulation by 1alpha,25(OH)(2)D(3) agonists.     

Isolation and characterization of the tobramycin biosynthetic gene cluster from Streptomyces tenebrarius

The biosynthetic gene cluster for tobramycin, a 2-deoxystreptamine-containing aminoglycoside antibiotic, was isolated from Streptomyces tenebrarius ATCC 17920. A genomic library of S. tenebrarius was constructed, and a cosmid, pST51, was isolated by the probes based on the core regions of 2-deoxy-scyllo-inosose (DOI) synthase, and L-glutamine:DOI aminotransferase and L-glutamine:scyllo-inosose aminotransferase. Sequencing of 33.9 kb revealed 24 open reading frames (ORFs) including putative tobramycin biosynthetic genes. We demonstrated that one of these ORFs, tbmA, encodes DOI synthase by in vitro enzyme assay of the purified protein. The catalytic residues of TbmA and dehydroquinate synthase were studied by homology modeling. The gene cluster found is likely to be involved in the biosynthesis of tobramycin.     

Somatic embryogenesis in <Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.: a histological examination of key developmental stages

A potential novel method of producing high-quality potato (Solanum tuberosum L.) nuclear seeds is through the process of somatic embryogenesis (SE). Somatic embryo formation has been successfully reported in many plant species, but in potato, reliable SE systems are still at the experimental stage. A key factor in the success of any SE system is the ability to discriminate SE-specific cellular structures from those emerging through an organogenic route. In the investigation reported here we attempted to discriminate the progression of specific stages of potato SE by histological means. Internodal segment (INS) explants from 4- to 6-week-old cv. Desiree in vitro cultures were successively cultured on SE induction (for 2 weeks) and expression/regeneration media (for 3 weeks) with and without 2,4-dichlorophenoxyacetic acid (5 M). Microscopic examination of histological slides prepared using INS explants at different stages revealed the presence of characteristic globular, heart and torpedo stages in the potato SE system along with other associated unique features such as protoderm development and discrete vascular connections. These results confirm the occurrence of potato SE as per the accepted definition of the term.Abbreviations 2,4-D 2,4-Dichlorophenoxyacetic acid - ELS Embryo-like structure(s) - INS Internodal segment(s) - PEM Proembryo mass - SE Somatic embryogenesis     

Deoxypreussomerins from Jatropha curcas: are they also plant metabolites?

Three deoxypreussomerins, palmarumycins CP1, JC1 and JC2, have been isolated from a collection of the stems of Jatropha curcas. The second and third compounds are antibacterial constituents which were characterized from spectral evidence. The X-ray crystallographic structure of palmarumycin JC1 was also studied. Deoxypreussomerins have been obtained here from a plant source in appreciable quantities.