UV-B response of cucumber seedlings grown under metal halide and high pressure sodium/deluxe lamps

UV-B-sensitive (Poinsett) and -insensitive (Ashley) cultivars of cucumber ( Cucumis sativus L.) were grown in growth chambers at 600 μmol m⁻²s⁻¹ of photosynthetically active radiation provided by metal halide (MH) or high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradiated 15 days from seeding for 6 h per day under 18. 2 kJ m⁻² day⁻¹ of biologically effective UV-B (UV-B_BE) radiation. One of the most pronounced effects of UV-B was a 27 to 78% increase in phenylalanine ammonialyase (PAL) activity. UV-B also increased total polyamines. Catalase and superoxide dismutase varied greatly in their response to UV-B. There were no interactive effects on PAL or catalase activity, or total polyamines. There was a UV × PAR source interaction for superoxide dismutase activity. UV-B increased chlorosis and decreased height, dry weight and leaf area. Stem elongation, biomass production, leaf enlargement and chlorosis were greater under HPS/DX lamps than under MH lamps. Chlorosis was greater in Poinsett than in Ashley and in lower leaves than in upper ones. Aside from chlorosis, there were no interactive effects of UV-B, PAR source or cultivar on any of the growth parameters measured, suggesting that the growth response of cucumber seedlings to UV-B is unaffected by PAR source or cultivar. Similarly, except for SOD activity, the biochemical response to UV-B was also not influenced by PAR source or cultivar.     

Microsatellite evolution in congeneric mammals: domestic and bighorn sheep

We compared genotypes at eight (AC)n microsatellite loci in domestic sheep (Ovis aries) and wild Rocky Mountain bighorn sheep (O. canadensis). The domestic sheep had greater genetic variation, higher allele-size variances, and larger allele sizes than the wild sheep. Accumulating evidence from higher taxonomic comparisons shows that these parameters are biased if microsatellite loci are selected in one taxon and used in another. Our results demonstrate similar biases between congeneric species. We compared standard measures of genetic variation, differentiation, and distance within and between species (H, D, FST) to newer measures based on allele-size variance (SW, SB, RST). The size-based distances better detected species-level divergence, but standard measures better distinguished allopatric populations. Empirical calibration of these measures at the subspecies level is needed to establish their useful ranges.      

Expression of carp-cdx1, a caudal homolog,in embryos of the carp,Cyprinus carpio

A carp caudal cDNA of 1.3 kb was cloned after screening an early segmentation stage cDNA library with a probe produced by PCR using conserved homeobox sequences as primers and genomic DNA as template. The homeobox gene was called carp-cdxl. The gene appears highly similar to other vertebrate caudal homologs, especially the zebrafish gene cdx(Zf-cad). The possible relationship to homeobox genes within the Hox-C gene complexes is discussed. A weak expression of the gene, detected by in situ hybridization, was found shortly before gastrulation (at 25% epiboly) in cells likely to have a posterior fate. During gastrulation expression became stronger. At the early segmentation stage, cells of the neural keel in the area of the prospective spinal cord expressed the gene. During the progression of segmentation, expression retracted in a caudal direction. The tailbud expressed the gene throughout, but the somites lost expression shortly after their formation. Only the most lateral mesoderm cells maintained expression in the trunk area. Carp-cdxl was also expressed in the endoderm. At 24 h after fertilization the gene was only expressed in the tailbud. At 48 h, no expression could be detected. The expression pattern suggests a function for carp-cdxl in gastrulation and patterning along the anterior-posterior axis of the embryo.     

Natural transmission of Salmonella choleraesuis in swine.

This experiment was designed to study the natural transmission of Salmonella choleraesuis in swine. Forty pigs were divided into three groups. Group 1 (n = 12) was challenged with 10(8) CFU of S. choleraesuis per ml by intranasal inoculation. One day postinoculation (p.i.), group 2 (n = 24) was commingled with group 1. Group 3 (n = 4) served as uninoculated controls. Serum samples were collected weekly. Blastogenesis assays and necropsies were performed at 1, 2, 4, 6, 9, and 12 weeks p.i., and 16 tissue samples per pig were collected and cultured. Environmental (pooled feces from the pen floor) levels of S. choleraesuis were 2.61 log10 CFU/g of feces at 24 h p.i. (immediately prior to commingling). Severe clinical signs were observed in groups 1 and 2. The results indicated that at least 16% of group 2 pigs were shedding S. choleraesuis within 24 h of commingling. At 1 week p.i., 32 of 32 group 1 and 39 of 62 group 2 tissue samples were positive for S. choleraesuis. Only 3 of 12 group 2 pigs were positive at 6, 9, and 12 weeks (1 pig for each week), indicating that only a small proportion of infected swine become long-term carriers. At 12 weeks p.i., only the colon and colonic lymph node samples of one pig from group 2 were positive. Humoral, mucosal, and cellular immune responses were similar between groups 1 and 2. These data demonstrate that a few pigs shedding low levels of Salmonella organisms before slaughter can result in rapid transmission and subsequent shedding by many swine.     

The interaction of edge-fixation and negative phototaxis in the orientation of walking gypsy moths,Lymantria dispar

Summary The visual orientation towards single black stripes and more complex patterns, comprising smooth gradients of brightness was studied in walking gypsy moths. Depending on the width of a black stripe, up to three walking directions are preferred within one stimulus situation: towards the centre of the stripe and towards a region within the stripe closer to each edge. The observed responses are explained by a compromise between edge-fixation and negative phototaxis. This hypothesis turned out to be also applicable to more complex patterns.     

Autocatalytic replication of a recombinant RNA

We demonstrate that a heterologous RNA sequence can be copied in vitro by Q beta replicase when it is inserted into a naturally occurring Q beta replicase template. A recombinant RNA was constructed by inserting decaadenylic acid between nucleotides 63 and 64 of MDV-1 (+) RNA, using phage T4 RNA ligase. The insert was located away from regions of the template known to be required for the binding of the replicase and for the initiation of product strand synthesis. To minimize the disruption of template structure, we inserted the heterologous sequence into a hairpin loop on the exterior of the molecule. Q beta replicase copied this recombinant RNA in vitro, and the complementary product strands served as templates for the synthesis of additional copies of the original recombinant RNA. The reaction was therefore autocatalytic and the amount of recombinant RNA increased exponentially. A 300-fold amplification of the recombinant RNA occurred within nine minutes. Insertion of biologically significant RNAs into the MDV-1 RNA sequence should allow them to be replicated autocatalytically.     

Bile salt-binding polypeptides in brush-border membrane vesicles from rat small intestine revealed by photoaffinity labeling

Photoaffinity labeling of small intestinal brush-border membrane vesicles with photolabile bile salt derivatives was performed to identify bile salt-binding polypeptides in these membranes. The derivatives used in this study were the sodium salts of 7,7-azo-3 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oic acid, 3 beta-azido-7 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oic acid, their respective taurine conjugates, and (11 xi-azido-12-oxo-3 alpha, 7 alpha-dihydroxy-5 beta-cholan-24-oyl)-2-aminoethanesulfonic acid. With ileal brush-border membrane vesicles, photoaffinity labeling resulted in the identification of 5 polypeptides with apparent molecular weights of 125,000, 99,000, 83,000, 67,000, and 43,000. The extent of labeling depended on the photolabile derivative employed. In jejunal brush-border membrane vesicles, polypeptides with apparent molecular weights of 125,000, 94,000, 83,000, 67,000, and 43,000 were labeled. The results indicate that the binding polypeptides involved in bile salt transport in ileal brush-border membrane vesicles are 1) similar with one exception to those concerned with bile salt transport in jejunal brush-border membranes, and 2) markedly different from those previously shown to be concerned with bile salt transport in plasma membranes of hepatocytes.     

Nucleotide sequence of the Acinetobacter calcoaceticus trpGDC gene cluster

A plasmid library of Acinetobacter calcoaceticus HindIII fragments was constructed, and clones that complemented an Escherichia coli pabA mutant were selected. Plasmids containing a 3.9-kb fragment of A. calcoaceticus DNA that also complemented E. coli trpD and trpC-(trpF+) mutants were obtained. We infer that complementation of E. coli pabA mutants was the result of the expression of the amphibolic anthranilate- synthase/p-aminobenzoate-synthase glutamine-amidotransferase gene and that the plasmid insert carried the entire trpGDC gene cluster. In E. coli minicells, the plasmid insert directed the synthesis of polypeptides of 44,000, 33,000, and 20,000 daltons, molecular masses that are consistent with the reported molecular masses of phosphoribosylanthranilate transferase, indoleglycerol-phosphate synthase, and anthranilate-synthase component II, respectively. A 3,105- bp nucleotide sequence was determined. Comparison of the A. calcoaceticus trpGDC sequences with other known trp gene sequences has allowed insight into (1) the evolution of the amphibolic trpG gene, (2) varied strategies for coordinate expression of trp genes, and (3) mechanisms of gene fusions in the trp operon.