Dynamic aspects and enhancement of leaf elongation in rice

Some dynamic aspects of leaf elongation in rice were studied. Under both well watered and water-deficient conditions, leaf elongation rates were 15 to 30% greater during the day than during the night. Night temperatures below 27 C limited the rate of elongation at night but when night temperatures exceeded 27 C, night elongation rates exceeded rates during the day. The diurnal pattern of elongation was opposite to the pattern of bulk leaf turgor which was lower during the day than at night.     

Population genomic evidence for multiple Pliocene refugia in a montane‐restricted harvestman (Arachnida,Opiliones, Sclerobunus robustus) from the southwestern United States

The integration of ecological niche modelling into phylogeographic analyses has allowed for the identification and testing of potential refugia under a hypothesis‐based framework, where the expected patterns of higher genetic diversity in refugial populations and evidence of range expansion of nonrefugial populations are corroborated with empirical data. In this study, we focus on a montane‐restricted cryophilic harvestman, Sclerobunus robustus, distributed throughout the heterogeneous Southern Rocky Mountains and Intermontane Plateau of southwestern North America. We identified hypothetical refugia using ecological niche models (ENMs) across three time periods, corroborated these refugia with population genetic methods using double‐digest RAD‐seq data and conducted population‐level phylogenetic and divergence dating analyses. ENMs identify two large temporally persistent regions in the mid‐latitude highlands. Genetic patterns support these two hypothesized refugia with higher genetic diversity within refugial populations and evidence for range expansion in populations found outside hypothesized refugia. Phylogenetic analyses identify five to six genetically divergent, geographically cohesive clades of S. robustus. Divergence dating analyses suggest that these separate refugia date to the Pliocene and that divergence between clades pre‐dates the late Pleistocene glacial cycles, while diversification within clades was likely driven by these cycles. Population genetic analyses reveal effects of both isolation by distance (IBD) and isolation by environment (IBE), with IBD more important in the continuous mountainous portion of the distribution, while IBE was stronger in the populations inhabiting the isolated sky islands of the south. Using model‐based coalescent approaches, we find support for postdivergence migration between clades from separate refugia.     

Effects of initial-link duration on preference and resistance to change in concurrent-chains schedules

Previous studies with concurrent-chains procedures have shown that preference for a terminal-link signaling a higher reinforcement rate decreases as initial-link durations increase. Using a concurrent-chains procedure, the present experiment examined the effects of manipulating initial-link duration on preference and resistance to disruption with rats nose poking for different rates of food reinforcement in the terminal links. Consistent with previous findings, preference for a terminal link with a higher reinforcement rate decreased with longer initial links. Conversely, relative resistance to disruption in the terminal link with a higher reinforcement rate increased with longer initial links. These findings are counter to the prediction of behavioral momentum theory that preference and resistance to change should be positively related.     

Role of Cortactin Homolog HS1 in Transendothelial Migration of Natural Killer Cells

Natural Killer (NK) cells perform many functions that depend on actin assembly, including adhesion, chemotaxis, lytic synapse assembly and cytolysis. HS1, the hematopoietic homolog of cortactin, binds to Arp2/3 complex and promotes actin assembly by helping to form and stabilize actin filament branches. We investigated the role of HS1 in transendothelial migration (TEM) by NK cells. Depletion of HS1 led to a decrease in the efficiency of TEM by NK cells, as measured by transwell assays with endothelial cell monolayers on porous filters. Transwell assays involve chemotaxis of NK cells across the filter, so to examine TEM more specifically, we imaged live-cell preparations and antibody-stained fixed preparations, with and without the chemoattractant SDF-1α. We found small to moderate effects of HS1 depletion on TEM, including whether the NK cells migrated via the transcellular or paracellular route. Expression of HS1 mutants indicated that phosphorylation of HS1 tyrosines at positions 222, 378 and 397 was required for rescue in the transwell assay, but HS1 mutations affecting interaction with Arp2/3 complex or SH3-domain ligands had no effect. The GEF Vav1, a ligand of HS1 phosphotyrosine, influenced NK cell transendothelial migration. HS1 and Vav1 also affected the speed of NK cells migrating across the surface of the endothelium. We conclude that HS1 has a role in transendothelial migration of NK cells and that HS1 tyrosine phosphorylation may signal through Vav1.     

Prototheca zopfii: Natural,transient, occurrence in pigs and rats

Domestic swine faeces and fresh faeces from trapped barnyard rats were heavily contaminated with Prototheca zopfii, a cause of dairy cow mastitis. When the pigs and rats were maintained on Prototheca-free diets, the transient intestinal population of P. zopfii decreased precipitously and disappeared. When combined with the information that other farm animals excrete P. zopfii, it was concluded that contaminated animal feed may be the source of large numbers of P. zopfii in the farm environment. We found P. zopfii in wet spoiled feed. Rats are logical vectors for contamination of feed.     

Solution structure of thioredoxin h1 from Arabidopsis thaliana

Present in virtually every species, thioredoxins catalyze disulfide/dithiol exchange with various substrate proteins. While the human genome contains a single thioredoxin gene, plant thioredoxins are a complex protein family. A total of 19 different thioredoxin genes in six subfamilies has emerged from analysis of the Arabidopsis thaliana genome. Some function specifically in mitochondrial and chloroplast redox signaling processes, but target substrates for a group of eight thioredoxin proteins comprising the h subfamily are largely uncharacterized. In the course of a structural genomics effort directed at the recently completed A. thaliana genome, we determined the structure of thioredoxin h1 (At3g51030.1) in the oxidized state. The structure, defined by 1637 NMR-derived distance and torsion angle constraints, displays the conserved thioredoxin fold, consisting of a five-stranded beta-sheet flanked by four helices. Redox-dependent chemical shift perturbations mapped primarily to the conserved WCGPC active-site sequence and other nearby residues, but distant regions of the C-terminal helix were also affected by reduction of the active-site disulfide. Comparisons of the oxidized A. thaliana thioredoxin h1 structure with an h-type thioredoxin from poplar in the reduced state revealed structural differences in the C-terminal helix but no major changes in the active site conformation.     

Regulation of tumor cell chemotaxis by type IV collagen is mediated by a Ca(2+)-dependent mechanism requiring CD47 and the integrin alpha(V)beta(3)

Studies from our laboratories demonstrated that synthetic peptides from the non-collagenous (NC-1) domain of the alpha3 (IV) chain of type IV collagen (COL IV) enhanced tumor cell adhesion (Han, J., Ohno, N., Monboisse, J. C., Pasco, S., Borel, J. P., and Kefalides, N. A. (1997) J. Biol. Chem. 272, 20395-20401). We have isolated the receptors for the alpha3(IV)185-203 peptide from melanoma and prostate tumor cells and identified them as CD47/integrin-associated protein and the integrin alpha(V)beta(3) (Shahan, T. A., Ziaie, Z., Pasco, S., Fawzi, A., Bellon, G., Monboisse, J. C., and Kefalides, N. A. (1999) Cancer Res. 59, 4584-4590). In the present study we have examined the effect of CD47 and the integrin alpha(V)beta(3) on in vitro tumor cell chemotaxis and Ca(2+)(i) modulation in response to COL IV, from the anterior lens capsule (ALC-COL IV) and peptides from its NC-1 domain. COL IV as well as the alpha3(IV) peptide promoted tumor cell chemotaxis with an immediate increase in intracellular [Ca(2+)]. Treating tumor cells with CD47 and integrin alpha(V)beta(3)-reactive antibodies reduced chemotaxis as well as the rise in [Ca(2+)](i) in response to ALC-COL IV or the alpha3(IV)185-203 peptide but not to Engelbreth-Holm-Swarm-COL IV or fibronectin. The alpha3(IV)185-203 synthetic peptide stimulated an increase in calcium from intracellular stores exclusively, whereas ALC-COL IV, Engelbreth-Holm-Swarm-COL IV, and fibronectin stimulated Ca(2+) flux from both internal and external stores. Furthermore, treatment of the cells with Ca(2+) chelator bis-(O-aminophenoxyl)ethane-N,N,N',N'-tetraaceticacid- acetomethoxy ester inhibited chemotaxis toward both ALC-COL IV and the alpha3(IV)185-203 peptide. These data indicate that CD47 and integrin alpha(V)beta(3) regulate tumor cell chemotaxis in response to COL IV and the alpha3(IV)185-203 peptide through a Ca(2+)-dependent mechanism.     

Tyrosine kinase activation in response to fungal spores is primarily dependent on endogenous reactive oxygen production in macrophages

Studies from our laboratory (Shahan, T. A., Sorenson, W. G., and Lewis, D. M. (1994) Environ. Res. 67, 98-104) demonstrated that spores from different fungal species differentially activate rat alveolar macrophages as detected by the measurement of superoxide anion and cytokine production (Shahan, T. A., Siegel, P. D., Sorenson, W. G., Kuschner, W. G., and Lewis, D. M. (1998) Am. J. Respir. Cell Mol. Biol. 18, 435-441). Spores from Aspergillus candidus stimulated production of the highest levels of superoxide anion (5.2 nmol/1.0 x 10(6) alveolar macrophages (AMs)/30 min), followed by those from Aspergillus niger (2.4 nmol/1.0 x 10(6) AMs/30 min) and Eurotium amstelodami (0.4 nmol/1.0 x 10(6) AMs/30 min). The mechanism of this differential activation was studied. Our data demonstrate that the tyrosine kinases p56(Hck), p72(Syk), p77(Btk), p62(Yes), p56(Lck), and p59(Fyn) were specifically activated in response to spores from A. candidus, whereas spores from either A. niger or E. amstelodami activated p56(Hck), p72(Syk), and p77(Btk). Kinetic analysis of specific tyrosine kinases demonstrated that p56(Hck), p72(Syk), and p77(Btk) were activated faster and to a greater extent by spores from A. candidus as compared with spores from E. amstelodami. These data suggest a relationship between reactive oxygen species and tyrosine kinase activation. Treatment of AMs with H(2)O(2) (1 mM) caused the activation of p72(Syk) only, whereas treatment with superoxide dismutase and catalase before treatment with the spores had no effect on tyrosine kinase activation. Incubation with NADPH oxidase inhibitors inhibited both superoxide anion production and the activation of p56(Hck), p72(Syk), and p77(Btk) in response to fungal spores. These data indicate that endogenous reactive oxygen species are necessary for the activation of p56(Hck), p72(Syk), and p77(Btk) by spores; they also indicate that some species of spores are capable of activating tyrosine kinases independent of superoxide anion.