The Nature of the Dietary Protein Impacts the Tissue-to-Diet 15N Discrimination Factors in Laboratory Rats

Due to the existence of isotope effects on some metabolic pathways of amino acid and protein metabolism, animal tissues are 15N-enriched relative to their dietary nitrogen sources and this 15N enrichment varies among different tissues and metabolic pools. The magnitude of the tissue-to-diet discrimination (Δ15N) has also been shown to depend on dietary factors. Since dietary protein sources affect amino acid and protein metabolism, we hypothesized that they would impact this discrimination factor, with selective effects at the tissue level. To test this hypothesis, we investigated in rats the influence of a milk or soy protein-based diet on Δ15N in various nitrogen fractions (urea, protein and non-protein fractions) of blood and tissues, focusing on visceral tissues. Regardless of the diet, the different protein fractions of blood and tissues were generally 15N-enriched relative to their non-protein fraction and to the diet (Δ15N>0), with large variations in the Δ15N between tissue proteins. Δ15N values were markedly lower in tissue proteins of rats fed milk proteins compared to those fed soy proteins, in all sampled tissues except in the intestine, and the amplitude of Δ15N differences between diets differed between tissues. Both between-tissue and between-diet Δ15N differences are probably related to modulations of the relative orientation of dietary and endogenous amino acids in the different metabolic pathways. More specifically, the smaller Δ15N values observed in tissue proteins with milk than soy dietary protein may be due to a slightly more direct channeling of dietary amino acids for tissue protein renewal and to a lower recycling of amino acids through fractionating pathways. In conclusion, the present data indicate that natural Δ15N of tissue are sensitive markers of the specific subtle regional modifications of the protein and amino acid metabolism induced by the protein dietary source

Biocontrol agents applied individually and in combination for suppression of soilborne diseases of cucumber

The soilborne pathogens Rhizoctonia solani, Pythium ultimum, and Meloidogyne incognita can cause severe economic losses to field- and greenhouse-grown cucumber. A collection of bacterial isolates and isolates GL3 and GL21 of Trichoderma virens were screened for suppression of diseases caused by these pathogens. T. virens isolates GL3 and GL21 provided the most effective suppression of damping-off caused by R. solani in greenhouse bioassays. Burkholderia ambifaria BC-F, B. cepacia BC-1, and Serratia marcescens N1-14 also provided significant suppression of R. solani relative to the pathogen check in some experiments. T. virens isolates GL3 and GL21 and S. marcescens isolates N1-6, N1-14, and N2-4 provided the most consistent and effective suppression of damping-off of cucumber caused by P. ultimum in growth chamber experiments. No microbial treatment containing individual or combined microbes significantly suppressed populations of M. incognita on cucumber or improved plant vigor in greenhouse bioassays. T. virens GL21 applied as a granular formulation, in combination with B. cepacia BC-1 or B. ambifaria BC-F applied as a seed treatment, significantly improved suppression of damping-off caused by R. solani over individual applications of these microbes in at least one experiment. Treatments combining B. cepacia BC-1, B. ambifaria BC-F, or S. marcescens isolates N1- 14 or N2-4 with T. virens GL21 in R. solani biocontrol assays always resulted in plant stands that were similar or greater than treatments containing individual applications of these microbes. B. ambifaria BC-F combined with T. virens GL21 in seed treatments resulted in significantly improved suppression of damping-off caused by P. ultimum in two of three experiments. Populations of T. virens GL3 and GL21 were both substantially reduced after coincubation with B. cepacia BC-1, or S. marcescens isolates N1-14 or N2-4 for 10 to 12 d in cucumber rhizospheres. Populations of T. virens GL21 were slightly reduced after coincubation with B. ambifaria BC-F. Results presented here substantiate other studies reporting enhanced biocontrol performance with certain combinations of biocontrol agents. These results also indicate that antagonism among combinations of biocontrol agents can vary with the assay system employed

Publishing international (joint venture) research for impact

Existing and potential scholars often ask whether it is possible to predict which articles will ultimately have large impact. A series of hypotheses were considered based on a citation analysis of 65 articles published from 1980 to 2003 regarding international joint ventures. It was found that a paper will tend to receive more citations as its age and the number of performance measures increases. Theory building papers tend to have more citations, followed by descriptive papers and finally hypothesis testing papers. Papers that appeared in tier 1 journals, and that considered theory in any way, explained a larger amount of the variance. Sample size was not an important predictor and explained little variance. Number of authors played no role. Collectively, the seven variables considered explained slightly less than two thirds of the total variance. Copyright Springer Science + Business Media, Inc. 2006