Effect of ploidy on the response of V79 cells to ionizing radiation

The responses of diploid, tetraploid and near-hexaploid V79 cells to X-irradiation or DNA-associated 125I-decay were compared. When cell killing, following X-irradiation, was plotted against the induced level of DNA double-strand breakage (dsb) per unit length of DNA, there was no significant difference between the relationships for each cell line. This suggested that the number of X-ray-induced DNA dsb per cell required to produce a lethal lesion was proportional to ploidy. Consistent with the X-ray results, tetraploid cells required 121 +/- 4 and diploid cells 60 +/- 1 125I-decays to produce a lethal lesion. However, the hexaploid cells deviated from this relationship and required 137 +/- 5 decays. The relationship between relative elution and 125I decays/cell reflected cellular DNA content. It is concluded that current models of radiation action are unable to explain these findings satisfactorily.     

The production and modification of cytochrome P-450 difference spectra by in vivo administration of methylenedioxyphenyl compounds

The in vivo administration of piperonyl butoxide (PB) or propyl isome (PI), both methylenedioxyphenyl compounds, to mice affects the levels of several hepatic cytochrome P-450 spectral interactions. The difference spectrum produced by carbon monoxide (commonly employed as a measurement of cytochrome P-450 levels) is initially lowered in magnitude by both compounds. The reduction is followed by an increase with time indicative of cytochrome induction. This biphasic effect, when produced by piperonyl butoxide, is accompanied by specific changes in the levels of the cytochrome P-450 difference spectra produced by hexobarbital, a type-I substrate, and pyridine, a type-II substrate. In addition, the ethyl isocyanide (EtNC) equilibrium point, calculated from the pH effect on the 455-nm and 430-nm peaks of the ethyl isocyanide-cytochrome P-450 difference spectrum, undergoes a biphasic shift. In contrast, propyl isome has the same effect on the substrate difference spectra as it does on the cytochrome level and produces no change in the ethyl isocyanide equilibrium point with time.     

Transposon-induced symbiotic mutants of Bradyrhizobium japonicum: isolation of two gene regions essential for nodulation

Summary Two strains of the soybean endosymbiont Bradyrhizobium japonicum, USDA 110 and 61 A101 C, were mutagenized with transposon Tn5. After plant infection tests of a total of 6,926 kanamycin and streptomycin resistant transconjugants, 25 mutants were identified that are defective in nodule formation (Nod^-) or nitrogen fixation (Fix^-). Seven Nod^- mutants were isolated from strain USDA 110 and from strain 61 A101 C, 4 Nod^- mutants and 14 Fix^- mutants were identified. Subsequent auxotrophic tests on these symbiotically defective mutants identified 4 His^- Nod^- mutants of USDA 110. Genomic Southern analysis of the 25 mutants revealed that each of them carried a single copy of Tn5 integrated in the genome. Three 61 A101 C Fix^- mutants were found to have vector DNA co-integrated along with Tn5 in the genome. Two independent DNA regions flanking Tn5 were cloned from the three nonauxotrophic Nod^- mutants and one His^-Nod^- mutant of USDA 110. Homogenotization of the cloned fragments into wild-type strain USDA 110 and subsequent nodulation assay of the resulting homogenotes confirmed that the Tn5 insertion was responsible for the Nod^- phenotype. Partial EcoR1 restriction enzyme maps around the Tn5 insertion sites were generated. Hybridization of these cloned regions to the previously cloned nod regions of R. meliloti and nif and nod regions of B. japonicum USDA 110 showed no homology, suggesting that these regions represent new symbiotic clusters of B. japonicum.     

A practical guide for restoration ecologists to manage microbial contamination risks before laboratory processes during microbiota restoration studies

Environmental microbiota are becoming more conventional components of restoration ecology studies due to their functional importance in ecosystems. Studying these microbiota offers insight into how they respond to, and potentially drive, ecosystem restoration. However, microbes are everywhere and therefore they pose a risk to sample integrity via uncontrolled contamination, and many of these risks are introduced before entering a molecular facility. Field ecologists who have limited experience in microbial and/or molecular studies may lack the knowledge on how to mitigate microbial contamination risks and, accordingly, may find rigorous collection of microbial samples a daunting task. Here, we present a practical guide that builds on our previous paper to help manage the risks of microbial contamination when undertaking a microbiota restoration study prior to entering a molecular facility. We cover study design and planning, undertaking field sampling, and sample transport and storage. We hope to provide a useful and practical guide to restoration ecologists who wish to include a microbiota component in their studies. If done well, this inclusion offers improved research quality and ultimately enhanced restoration outcomes.     

Effect of n-octylamine on the reduction of mammalian hepatic microsomal cytochrome b5

1. In a preceding paper evidence was presented for the endogenous reduction of NAD(P)+ by mammalian hepatic microsomes and the concomitant reduction of cytochrome b5. The experiments reported here demonstrate that low concentrations of n-octylamine, in the presence of limiting quantities of NAD+, cause an increased level of cytochrome b5 reduction by mouse hepatic microsomes and also delays its reoxidation. 2. These effects are both NAD+ and n-octylamine dependent and appear to be due to an activation of the microsomal enzyme causing endogenous reduction of NAD(P)+ and also, in part, to inhibition of the autooxidation of reduced cytochrome b5. 3. Protection from the inhibitory action of sulfhydryl reagents on NADH-cytochrome b5 reductase was also observed in the presence of n-octylamine. 4. The results suggest that the enzyme(s) involved in the endogenous reduction of NAD(P)+ is not the microsomal alcohol dehydrogenase.