Estimating abundance and spatial distribution patterns of the bubble crab Dotilla fenestrata (Crustacea: Brachyura)

Abstract The bubble crab Dotilla fenestrata forms very dense populations on the sand flats of the eastern coast of Inhaca Island, Mozambique, making it an interesting biological model to examine spatial distribution patterns and test the relative efficiency of common sampling methods. Due to its apparent ecological importance within the sandy intertidal community, understanding the factors ruling the dynamics of Dotilla populations is also a key issue. In this study, different techniques of estimating crab density are described, and the trends of spatial distribution of the different population categories are shown. The studied populations are arranged in discrete patches located at the well‐drained crests of nearly parallel mega sand ripples. For a given sample size, there was an obvious gain in precision by using a stratified random sampling technique, considering discrete patches as strata, compared to the simple random design. Density average and variance differed considerably among patches since juveniles and ovigerous females were found clumped, with higher densities at the lower and upper shore levels, respectively. Burrow counting was found to be an adequate method for large‐scale sampling, although consistently underestimating actual crab density by nearly half. Regression analyses suggested that crabs smaller than 2.9 mm carapace width tend to be undetected in visual burrow counts. A visual survey of sampling plots over several patches of a large Dotilla population showed that crab density varied in an interesting oscillating pattern, apparently following the topography of the sand flat. Patches extending to the lower shore contained higher densities than those mostly covering the higher shore. Within‐patch density variability also pointed to the same trend, but the density increment towards the lowest shore level varied greatly among the patches compared.     

Structure of hybrid backbone methylphosphonate DNA heteroduplexes: effect of R and S stereochemistry.

Methyl phosphonate oligonucleotides have been used as antisense and antigene agents. Substitution of a methyl group for oxygen in the phosphate ester backbone introduces a new chiral center. Significant differences in physical properties and hybridization abilities are observed between the R(p) and S(p) diastereomers. Chirally pure methylphosphonate deoxyribooligonucleotides were synthesized, and the solution structures of duplexes formed between a single strand heptanucleotide methylphosphonate, d(Cp(Me)Cp(Me)Ap(Me)Ap(Me)Ap(Me)Cp(Me)A), hybridized to a complementary octanucleotide, d(TpGpTpTpTpGpGpC), were studied by NMR spectroscopy. Stereochemistry at the methylphosphonate center for the heptanucleotide was either RpRpRpRpRpRp (R(p) stereoisomer) or RpRpRpSpRpRp (S(p) stereoisomer, although only one of the six methylphosphonate centers has the S(p) stereochemistry). The results show that the methylphosphonate strands in the heteroduplexes exhibit increased dynamics relative to the DNA strand. Substitution of one chiral center from R(p) to S(p) has a profound effect on the hybridization ability of the methylphosphonate strand. Sugars in the phosphodiester strand exhibit C(2)(') endo sugar puckering while the sugars in the methyl phosphonate strand exhibit an intermediate C(4)(') endo puckering. Bases are well stacked on each other throughout the duplex. The hybridization of the methylphosphonate strand does not perturb the structure of the complementary DNA strand in the hetero duplexes. The sugar residue 5' to the S(p) chiral center shows A-form sugar puckering, with a C(3)(')-endo conformation. Minor groove width in the R(p) stereoisomer is considerably wider, particularly at the R(p) vs S(p) site and is attributed to either steric interactions across the minor groove or poorer metal ion coordination within the minor groove.     

Pathogenicity of six isolates of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina, Hyphomycetes) to Perillus bioculatus (F) (Hem., Pentatomidae)

Abstract:  The two-spotted stink bug, Perillus bioculatus (F) (Hem., Pentatomidae) is considered an important predator of Colorado potato beetle egg masses and small larvae. The susceptibility of P. bioculatus second instar nymphs to six isolates of Beauveria bassiana (Balsamo) Vuillemin, which are highly pathogenic to Colorado potato beetle, was tested in the laboratory. Five isolates were highly pathogenic and caused more than 77% mortality after 8 days at a concentration of 10⁶ conidia/ml. However, isolate IPP46 showed low pathogenicity and caused only 11% mortality of nymphs. The pathogenicity of isolates was independent of their host, source or country of origin. Isolate IPP46 was tested at six different concentrations. A linear relationship between the concentration of B. bassiana and the mortality of nymphs was observed. The 50% lethal concentration (LC₅₀) value was 3.4 × 10⁷ conidia/ml. The LT₅₀ decreased with increase of conidia concentration used. The present results suggest that isolate IPP46 has good potential as a biological control agent within an integrated pest management programme.     

Effects of low temperature,genotype and culture media on in vitro androgenic answer of pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.)

Anther culture is one of the most important and useful tool to create pure lines for plant breeding programs rapidly. Some pepper genotypes are recalcitrant and embryogenic frequency in anther culture is still low or reaction is not observed at all. Temperature stress (low or high) can facilitate switching the microspore to sporophyte developmental pathway. In this study, some differences were found in embryogenic reaction among the pepper genotypes and culture media variants, depending on duration of cold treatment of flower buds. Experimental results indicated that embryogenic efficiency decreased under low-temperature stress. Nevertheless, positive effect of cold pretreatment on direct embryo induction was obtained in four genotypes—cultivar Hebar, hybrid 50/01 and lines 668/02 and 1312/02. Increasing of embryogenic reaction after cold pretreatment was observed in media variants C (24 h) and MS-3 + (24 and 48 h), while on medium variant C-0 direct embryo formation was registered only after 48 h cold pretreatment. These results show that the donor genotypes have specific requirements for type and duration of temperature pretreatment and also culture media for induction of androgenesis with higher frequency.     

Paradoxical Enhancement of the Activity of a Bacterial Multidrug Transporter Caused by Substitutions of a Conserved Residue

Substitution of threonine or serine for the evolutionary conserved intramembrane proline P³⁴⁷ of the Bacillus subtilis multidrug transporter Bmr significantly increases the toxin-effluxing activity of Bmr without affecting its abundance in the cell. In cocultivation experiments, we demonstrate that although the mutant T³⁴⁷ Bmr is advantageous to cells growing in the presence of a toxin, the wild-type P³⁴⁷ Bmr is advantageous under the conditions of nutritional limitation. This may explain why Bmr has evolved the way it did, that is, with proline at position 347. These observations provide a basis for speculating that the evolution of Bmr has been determined by its presently unidentified natural function rather than by its ability to expel diverse toxins from the cell.     

Three Novel <Emphasis Type="Italic">NF1</Emphasis> Gene Mutations in a Cohort of Bulgarian Neurofibromatoses Patients

Neurofibromatosis (NF) is a clinically heterogeneous autosomal dominant disorder. Three distinct forms have been identified: neurofibromatosis type 1 (NF1), type 2 (NF2) and schwannomatosis. In the present study, we report clinical and genetic findings in the NF1 and NF2 genes in a cohort of 27 Bulgarian patients, with 18 cases (67%) genetically verified. Both NF1 and NF2 genes were screened by Sanger sequencing on DNA samples. The Sanger negative samples were screened by Multiplex Ligation-dependent Probe Amplification (MLPA) for deletions and duplications. The results from genetic testing revealed three novel mutations and fifteen previously reported ones (13 in the NF1 gene and 2 in the NF2 gene). The novel variants in the NF1 gene are a splice site mutation c.4725-1G>A, a small deletion of five bases c.823delATCTT, p.Leu275ValfsTer14, and a single base duplication c.6547dupC, p.Arg2183ProfsTer11. The novel splice site mutation is manifested by multiple “café au lait” macules and neurofibromas. Both novel out of frame mutations were found in patients with multiple “café au lait” spots and focal epilepsy. A segmental neurofibromatosis (SNF1) is restricted to one or more body segments. Here we present a case with SNF1 caused by a somatic deletion of exons 1 to 12 of the NF1 gene which is manifested by multiple neurofibromas in the right hand. Two nonsense mutations are found in the NF2 gene. Our study adds three novel mutations to the NF1 mutation spectra and contributes to the clinical-genetic NF1-characterization. Here we report strikingly different phenotypic spectra caused by the same mutation in a single family. Our findings contribute to the genotype- phenotype correlations which are difficult to establish, due to the extremely complex NF phenotype being a combination of clinical features.     

Small Intestine Microbiota Regulate Host Digestive and Absorptive Adaptive Responses to Dietary Lipids

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Influence of cytokinins and novel cytokinin antagonists on the senescence of detached leaves of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Cytokinins N⁶-benzyladenine (BA) and 1-(2-chloropyridin-4-yl)-3-phenylurea (4PU-30) delayed the senescence of detached leaves (3^rd to 7^th leaf node) of wild and ethylene insensitive eti5 mutant of Arabidopsis thaliana. The novel anticytokinins, structural analogues of purine and phenylurea cytokinins also affected the senescence of detached rosette leaves of A. thaliana. They diminished to a significant extent the cytokinin-induced delay of chlorophyll destruction, but without a considerable difference in their action against both types of cytokinins. These results correlated with changes observed in ribonuclease (RNase) activity.     

Role of a serine/threonine kinase,Mst1, in megakaryocyte differentiation

Platelets, which play a central role in thrombosis and hemostasis, develop from megakaryocytes. Signal transduction originated from the megakaryocyte growth and development factor, the Mpl ligand, which leads to megakaryocyte differentiation, polyploidization, and maturation, has been gradually characterized. In this study, we report the inducibility of Mst1, a recently described serine/threonine kinase, by Mpl ligand and the effect of its induced expression on megakaryocyte differentiation. The steady‐state level of mst1 message and Mst1‐associated kinase activity increased in response to Mpl ligand. Ectopic expression of human mst1 in a mouse megakaryocytic cell line resulted in a drastic increase in DNA content per cell. Elevated expression of megakaryocyte differentiation markers, such as acetylcholine esterase, PF4, and GPIIb was also observed in hmst1‐expressing cells. Activation of p38 MAPK, a known downstream effector of Mst1, was shown to be required for polyploidization, but not for enhanced expression of differentiation markers. Our study thus designates Mst1 as a Mpl ligand‐responsive signaling molecule that promotes induction of lineage‐specific cellular programming. J. Cell. Biochem. 76:44–60, 1999. © 1999 Wiley‐Liss, Inc.