The relative toxicity of a spore preparation of Bacillus thuringiensis var. israelensis against fourth instar larvae of Aedes aegypti and Toxorhynchites amboinensis: suspension feeding compared with enemas and forced feeding

The toxic effect of a spore preparation of Bacillus thuringiensis var. israelensis Berliner Serotype H-14 (Bti) on 4th instar larvae of Aedes aegypti L. and Toxorhynchites amboinensis (Doleschall) was observed when given either in a suspension feeding test or when injected orally as a forced feeding or via the anus as an enema. The A. aegypti larvae showed the greater sensitivity to Bti both because they greatly concentrate the toxin by filter feeding and they are more sensitive to Bti than are the larvae of T. amboinensis. The latter appeared approximately two-fold less sensitive to Bti than the former after taking into account their greater body weight.

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Résumé La toxicité sur des larves de 4ème stade de A. aegypti et T. amboinensis, d'une préparation de spores de B. thuringiensis var. israelensis Berliner sérotype H-14, a été examinée après: injection orale par alimentation forcée, injection anale comme lavement, — le témoin étant une alimentation à partir d'une suspension de spores.Les larves de A. aegypti ont présenté la plus grande sensibilité au Bti d'une part parce qu'elles concentrent beaucoup la toxine avec leur alimentation par filtration, et parce qu'elles sont plus sensibles sensu stricto au Bti. Même en tenant compte de leur poids plus élevé, T. amboinensis est apparu comme deux fois moins sensible au Bti.

     

Characterization of base-pair opening in deoxynucleotide duplexes using catalyzed exchange of the imino proton

Using nuclear magnetic resonance line broadening, longitudinal relaxation and magnetization transfer from water, we have measured the imino proton exchange times in the duplex form of the 10-mer d-CGCGATCGCG and in seven other deoxy-duplexes, as a function of the concentration of exchange catalysts, principally ammonia. All exchange times are catalyst dependent. Base-pair lifetimes are obtained by extrapolation to infinite concentration of ammonia. Lifetimes of internal base-pairs are in the range of milliseconds at 35 degrees C and ten times more at 0 degrees C. Lifetimes of neighboring pairs are different, hence base-pairs open one at a time. Lifetimes of d(G.C) are about three times longer than those of d(A.T). The nature of neighbors usually has little effect, but lifetime anomalies that may be related to sequence and/or structure have been observed. In contrast, there is no anomaly in the A.T base-pair lifetimes of d-CGCGA[TA]5TCGCG, a model duplex of poly[d(A-T)].poly[d(A-T)]. The d(A.T) lifetimes are comparable to those of r(A.U) that we reported previously. End effects on base-pair lifetimes are limited to two base-pairs. The low efficiency of exchange catalysts is ascribed to the small dissociation constant of the deoxy base-pairs, and helps to explain why exchange catalysis had been overlooked in the past. This resulted in a hundredfold overestimation of base-pair lifetimes. Cytosine amino proteins have been studied in the duplex of d-CGm5CGCG. Exchange from the closed base-pair is indicated. Hence, the use of an amino exchange rate to evaluate the base-pair dissociation constant would result in erroneous, overestimated values. Catalyzed imino proton exchange is at this time the safest and most powerful, if not the only probe of base-pair kinetics. We propose that the single base-pair opening event characterized here may be the only mode of base-pair disruption, at temperatures well below the melting transition.     

Biochemical and spectroscopic characterization of the high molecular weight cytochrome c from Desulfovibrio vulgaris Hildenborough expressed in Desulfovibrio desulfuricans G200.

The gene of high molecular weight, multiheme cytochrome c (Hmc) from the sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough has been overexpressed in Desulfovibrio desulfuricans G200. The recombinant protein has been purified. Its molecular weight (65,600), amino acid composition, and NH2-terminal sequence were found to be identical to those of the wild-type protein. The recombinant protein has been spectroscopically characterized (optical spectrum, EPR, circular dichroism) and compared to the wild-type protein. We have found 16 hemes per molecule by iron analysis and the pyridine hemochrome test. Both high- and low-spin features were observed in the EPR spectrum. A detailed spin quantitation analysis indicates 1 or 2 high-spin hemes and 14 or 15 low-spin hemes per molecule. The redox potentials of the hemes determined by voltammetric techniques gave an average of three different values, 0, -100, and -250 mV (versus NHE), for the wild-type and the recombinant cytochrome. The low potential values are similar to the values observed for the bis(histidinyl) coordinated hemes of cytochrome c3. A comparison of the arrangement of heme binding sites and coordinated histidines in the amino acid sequences of cytochrome c3 and Hmc has shown that the latter contains four domains, three of which are complete c3-like domains, while the fourth represents an incomplete c3-like domain which may contain His-Met coordinated hemes. These data are in agreement with the detailed study of the number and types of hemes reported in this paper.     

Genetic variation inMeloidogyne incognita virulence against the tomatoMi resistance gene: evidence from isofemale line selection studies

Resistance to the parthenogenetic root-knot nematodeMeloidogyne incognita is controlled in tomato by the single dominant geneMi, against which virulent pathotypes are able to develop. Isofemale lines (i.e., families) were established from a natural avirulent isolate ofM. incognita in order to study the genetic variability and inheritance of the nematode virulence. From the progeny of individual females, the production of egg masses on the root system of theMi-resistant tomato Piersol was analyzed in artificial selection experiments. A family analysis revealed, after two successive generations, a strongly significant variation between the 63 isofemale lines tested, and the results obtained for the mothers and their daughters were also significantly correlated. These results together clearly demonstrate the existence of a genetic variability and inheritance for this character. In a second experiment, a four-generation selection was performed on 31 other isofemale lines. The results revealed a significant response to selection apparently limited only to the two families able to produce, in first generation, a significant minimal egg-mass number on the resistant cultivar.     

PCR-mediated screening and labeling of DNA from clones

A simplified and economical protocol for DNA library screening and nonradioactive labeling is described. Bacterial clones are lysed in 1% of Triton X-100 and subjected to polymerase chain reaction in the presence of digoxigenin-11-dUTP to screen and simultaneously to label the DNA inserts. Bacteriallysates are stable in storage at −20°C and can be used repeatedly for PCR-mediated labeling. In this protocol, very low concentrations of dNTP, digoxigenin-dUTP, and primers are used in combination with a reduced reaction volume. This will considerably reduce the expense of screening and labeling bacterial clones and facilitate the exchange of DNA probes among laboratories.     

Molecular mapping of wheat. Homoeologous group 2.

A molecular-marker map of bread wheat having many markers in common with other grasses in the Gramineae family is a prerequisite for molecular level genetic studies and breeding in this crop species. We have constructed restriction fragment length polymorphism maps of the A-, B-, and D-genome chromosomes of homoeologous group 2 of hexaploid wheat (Triticum aestivum L. em. Thell) using 114 F7 lines from a synthetic x bread wheat cross and clones from 11 libraries. Chromosomes 2A, 2B, and 2D comprise 57, 60, and 56 markers and each spans about 200 cM. Comparisons between chromosomes are facilitated by 26 sets of homoeoloci. Genes mapped include a heterologous abscisic acid responsive locus cloned as pBS128, the epidermal waxiness inhibitor W21, and two presumed leaf rust and stem rust resistance genes. Anomalies suggesting ancestral rearrangements in chromosome 2B are pointed out and features of wheat group 2 chromosomes that are common to barley (Hordeum vulgare L.), rice (Oryza spp.), and T. tauschii are discussed.