Inheritance of random amplified polymorphic DNA markers in cassava (Manihot esculenta Crantz)

The informativeness and inheritance of randomly amplified polymorphic DNA (RAPD) markers were investigated in an intraspecific F1 progeny derived from two heterozygous parents. The analysis confirmed the utility of RAPD markers for comparing candidate parents for the development of a molecular genetic map, and provided numerous markers for linkage analysis in a crop with a very limited history of classical or molecular genetic studies. Six potential parental lines (themselves F1 hybrid clones) showed between 1.82 and 0.62 segregating bands per primer in three hybrid families. Forty-three percent (309) of 722 primers produced polymorphic products in the most informative of these three crosses, revealing 328 single-dose (SD) markers segregating 1:1 for presence/absence in a progeny of 90 individuals. A second class of informative markers were those present in both parents but segregating in the progeny. Fifty-seven or 67% of the monomorphic but segregating markers exhibited the 3:1 ratio expected for SD dominant markers in a cross between heterozygotes. Linkage groups were constructed from the segregation of SD RAPD markers originating in the female (TMS 30572) and the male (CM2177-2) parent. Key words : RAPDs, molecular markers, genetic segregation, Manihot, single-dose markers.     

Isolation of the MurineNbr1Gene Adjacent to the MurineBrca1Gene

The humanNBR1cDNA has previously been identified using polyclonal sera to CA125, an ovarian tumor antigen used in monitoring ovarian cancer. The gene was mapped to theBRCA1region on chromosome 17q21 and subsequently found to lie in close proximity to the recently identifiedBRCA1gene. The NBR1 protein has a B-box motif but the function of the protein is as yet unknown. To investigate the function and importance of this gene, we have studied the conservation of this gene in other species and in particular in the mouse. We have isolated murineNbr1cDNA and genomic clones. Translation of the cDNA sequence indicates that the protein is highly conserved, being 89% similar and 84% identical to the human. Analysis of the murineNbr1genomic clones indicates that it maps less than 1 kb from theBrca1gene and that, unlike that in human, this region is not duplicated.     

Phosphorylation of glucose by a guanosine-5′-triphosphate (GTP)-dependent glucokinase in Fibrobacter succinogenes subsp. succinogenes S85

Cell extracts of Fibrobacter succinogenes subsp. succinogenes S85 phosphorylated glucose with a GTP-dependent glucokinase. The enzyme showed little activity with ATP (12% of that with GTP). Of other phosphate donors tested, only dGTP and ITP gave high glucokinase activities. Dialyzed extracts required Mg⁺² and K⁺ for maximal activity. In potassium phosphate buffer, glucokinase showed maximum activity at pH 7.5 with glucose-6-phosphate dehydrogenase as the coupling enzyme. In this assay, glucokinase was active with glucose (100%), 2-deoxy-d-glucose (40%), and mannose (20%). Partially purified glucokinase had a molecular weight of 82,000 and a pl of 4.82. Double-reciprocal plots of substrate concentration versus velocity were linear and the enzyme had apparent K_m values of 55 M for glucose and 72 M for GTP. Dialyzed cell extracts of Fibrobacter intestinalis C1A also contained a GTP-dependent glucokinase that showed little activity with ATP. Potassium also stimulated the activity of this enzyme. These results suggest that this unusual glucokinase may be characteristic of the genus Fibrobacter.Abbreviations CHES cyclohexylaminoethanesulfonic acid - GK glucokinase - PEP phosphoenolpyruvate Published with the approval of the Director of the North Dakota Agricultural Experiment Station as journal article no. 2186     

Influence of Plumbing Materials on Biofilm Formation and Growth of Legionella pneumophila in Potable Water Systems

A two-stage chemostat model of a plumbing system was developed, with tap water as the sole nutrient source. The model system was populated with a naturally occurring inoculum derived from an outbreak of Legionnaires' disease and containing Legionella pneumophila along with associated bacteria and protozoa. The model system was used to develop biofilms on the surfaces of a range of eight plumbing materials under controlled, reproducible conditions. The materials varied in their abilities to support biofilm development and the growth of L. pneumophila. Elastomeric surfaces had the most abundant biofilms supporting the highest numbers of L. pneumophila CFU; this was attributed to the leaching of nutrients for bacterial growth from the materials. No direct relationship existed between total biofouling and the numbers of L. pneumophila CFU.     

Inhibition of Aflatoxin Production by Surfactants

The effect of 12 surfactants on aflatoxin production, growth, and conidial germination by the fungus Aspergillus flavus is reported. Five nonionic surfactants, Triton X-100, Tergitol NP-7, Tergitol NP-10, polyoxyethylene (POE) 10 lauryl ether, and Latron AG-98, reduced aflatoxin production by 96 to 99% at 1% (wt/vol). Colony growth was restricted by the five nonionic surfactants at this concentration. Aflatoxin production was inhibited 31 to 53% by lower concentrations of Triton X-100 (0.001 to 0.0001%) at which colony growth was not affected. Triton X-301, a POE-derived anionic surfactant, had an effect on colony growth and aflatoxin production similar to that of the five POE-derived nonionic surfactants. Sodium dodecyl sulfate (SDS), an anionic surfactant, and dodecyltrimethylammonium bromide, a cationic surfactant, suppressed conidial germination at 1% (wt/vol). SDS had no effect on aflatoxin production or colony growth at 0.001%. The degree of aflatoxin inhibition by a surfactant appears to be a function of the length of the hydrophobic and hydrophilic chains of POE-derived surfactants.     

EVOLUTIONARY INTERACTIONS BETWEEN SEXUAL AND ALL-FEMALE TAXA OF CYPRINOTUS (OSTRACODA: CYPRIDIDAE)

Freshwater ostracodes show both an exceptionally high incidence of transitions to unisexuality and, in some cases, an extraordinary level of clonal diversity. There is no understanding of the agents promoting these transitions to thelytoky, although it has been suggested that their frequency may set the stage for sexual taxa to infuse clonal diversity into unisexuals. This study examines the nature and origins of clonal diversity in the unisexual ostracode Cyprinotus incongruens. A combination of allozyme and cytogenetic studies revealed the presence of two diploid clones of this species at three temperate sites and ten clones at one arctic site including three diploids, five triploids, and two tetraploids. The low heterozygosity (0%–20%) of its diploid clones suggests that parthenogenesis has arisen spontaneously in C. incongruens rather than through hybridization, as in vertebrate asexuals. Polyploid clones appear to owe their origin to genome additions from sexual taxa, although subsequent mutational divergence has played a role in further enhancing diversity. Two triploid clones have apparently originated from the incorporation of a haploid genome from the sexually reproducing C. glaucus, as evidenced by their high heterozygosity and possession of alleles otherwise found only in that species. Other polyploid clones have likely arisen as a result of interbreeding between bisexual and unisexual C. incongruens. These results suggest that both the incidence of spontaneous transitions to clonality and the frequency of interbreeding with relatives may be the key processes that govern clonal diversity in unisexual ostracodes.     

Non-photochemical fluorescence quenching and the diadinoxanthin cycle in a marine diatom

The diadinoxanthin cycle (DD-cycle) in chromophyte algae involves the interconversion of two carotenoids, diadinoxanthin (DD) and diatoxanthin (DT). We investigated the kinetics of light-induced DD-cycling in the marine diatom Phaeodactylum tricornutum and its role in dissipating excess excitation energy in PS II. Within 15 min following an increase in irradiance, DT increased and was accompanied by a stoichiometric decrease in DD. This reaction was completely blocked by dithiothreitol (DTT). A second, time-dependent, increase in DT was detected 20 min after the light shift without a concomitant decrease in DD. DT accumulation from both processes was correlated with increases in non-photochemical quenching of chlorophyll fluorescence. Stern-Volmer analyses suggests that changes in non-photochemical quenching resulted from changes in thermal dissipation in the PS II antenna and in the reaction center. The increase in non-photochemical quenching was correlated with a small decrease in the effective absorption cross section of PS II. Model calculations suggest however that the changes in cross section are not sufficiently large to significantly reduce multiple excitation of the reaction center within the turnover time of steady-state photosynthetic electron transport at light saturation. In DTT poisoned cells, the change in non-photochemical quenching appears to result from energy dissipation in the reaction center and was associated with decreased photochemical efficiency. D1 protein degradation was slightly higher in samples poisoned with DTT than in control samples. These results suggest that while DD-cycling may dynamically alter the photosynthesis-irradiance response curve, it offers limited protection against photodamage of PS II reaction centers at irradiance levels sufficient to saturate steady-state photosynthesis.Abbreviations CAP chloramphenicol - D1 PS II reaction center protein - DD diadinoxanthin - DD cycle-diadinoxanthin cycle - DT diatoxanthin - DTT dithiothreitol - FCP fucoxanthin chlorophyll a-c protein - F_m maximum fluorescence yield in the dark-adapted state - F_o minimum fluorescence yield in the dark-adapted state - F_m and F_o maximum and minimum fluorescence yields respectively in some light adapted state - F_v maximum variable fluorescence yield in the dark-adapted state - I_k Irradiance at the intercept of the initial slope of the photosynthesis-irradiance curve and the maximum photosynthetic rate - k_D first order rate constant for nonradiative de-excitation of excitions in the PS II antenna - k_d first order rate constant for non-radiative de-excitation of excitons in the PS II reaction center - k_F first order rate constant for fluorescence - k_T first order rate constant for exciton transfer to the reaction center - k_t first order rate constant for exciton transfer from the reaction center to the antenna - Rubisco ribulose bisphosphate carboxylase - SV_m Stern-Volmer quenching coefficient of the maximum fluorescence yield - SV_o Stern-Volmer quenching coefficient of the miniximum fluorescence yield - _{PS II} apparent absorption cross-section of PS II - _arr average interval between exciton arrival to the PS II reaction center (ms) - _rem average interval between electron turnover during photosynthesis in the PS II reaction center (ms) - _d the probability that an exciton is non-radiatively dissipated in the reaction center - _T the probability that an exciton in the antenna is transferred to the reaction center - _t the probability that an exciton is transferred back from the reaction center to the antenna     

Temperature-dependent development in marine copepods: a comparative analysis of models

A comparative analysis was carried out on the several equationsmost commonly used to describe the dependence of the developmentof organisms on temperature. Goodness of fit, number of parameters,ease of fitting data and biological significance were compared.     

Modulation by angiotensin III of nociception-related and arterial pressure-related neuronal responsiveness in the nucleus reticularis gigantocellularis of the rat

We evaluated possible modulation by angiotensin III (AIII) of the interactive effect of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Combined extracellular single-neuron recording and microiontophoresis were carried out on male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. The responsiveness of NRGC neurons to nociception (tail clamp) and/or transient hypertension elicited by phenylephrine (5 μg/kg, i.v.), in the absence or presence of AIII, was used as the experimental index. Microiontophoretic application of the heptapeptide suppressed the responses of spontaneously active NRGC neurons to individually delivered nociception or hypertension. Interestingly, the preferential reduction in responsiveness to tail clamp upon simultaneous elevation in arterial pressure was reversed to one that favored nociception in the presence of AIII. These actions of the heptapeptide appeared to be receptor-specific, since they were discernibly blocked by its selective antagonist, Ile⁷-angiotensin III. Our results reveal that neuropeptides such as AIII may differentially modulate neuronal responsiveness according to the prevailing physiologic input(s) to the central nervous system of the animal.