QTL and candidate genes phytoene synthase and zeta-carotene desaturase associated with the accumulation of carotenoids in maize

Carotenoids are a class of fat-soluble antioxidant vitamin compounds present in maize ( Zea mays L.) that may provide health benefits to animals or humans. Four carotenoid compounds are predominant in maize grain: beta-carotene, beta-cryptoxanthin, zeaxanthin, and lutein. Although beta-carotene has the highest pro-vitamin A activity, it is present in a relatively low concentration in maize kernels. We set out to identify quantitative trait loci (QTL) affecting carotenoid accumulation in maize kernels. Two sets of segregating families were evaluated-a set of F2:3 lines derived from a cross of W64a x A632, and their testcross progeny with AE335. Molecular markers were evaluated on the F2:3 lines and a genetic linkage map created. High-performance liquid chromatography was performed to measure beta-carotene, beta-cryptoxanthin, zeaxanthin, and lutein on both sets of materials. Composite interval mapping identified chromosome regions with QTL for one or more individual carotenoids in the per se and testcross progenies. Notably QTL in the per se population map to regions with candidate genes, yellow 1 and viviparous 9, which may be responsible for quantitative variation in carotenoids. The yellow 1 gene maps to chromosome six and is associated with phytoene synthase, the enzyme catalyzing the first dedicated step in the carotenoid biosynthetic pathway. The viviparous 9 gene maps to chromosome seven and is associated with zeta-carotene desaturase, an enzyme catalyzing an early step in the carotenoid biosynthetic pathway. If the QTL identified in this study are confirmed, particularly those associated with candidates genes, they could be used in an efficient marker-assisted selection program to facilitate increasing levels of carotenoids in maize grain.

The relationships and susceptibilities of some industrial, laboratory and clinical isolates of Pseudomonas aeruginosa to some antibiotics and biocides

AIMS

To provide evidence to support or refute the hypothesis that cross-resistance between antibiotics and biocides can occur.

METHODS AND RESULTS

Fifty-five strains of Pseudomonas aeruginosa were tested for their resistance to anti-pseudomonal antibacterials. Twenty clinical, 19 industrial and 16 culture collection isolates were used. The MIC was found for the antibiotics amikacin, ceftazidime, ciprofloxacin, gentamycin, ticarcillin, tobramycin, imipenem and polymyxin B. The MIC was also found for the biocides benzalkonium chloride and chlorhexidine. The analysis of the data was based on the production of a normal distribution of the log (MIC) plots for each antimicrobial. Strains were then labelled as resistant, intermediate or sensitive based on the mean and standard deviation of the distributions.

CONCLUSIONS

In general the clinical isolates were the most recalcitrant organisms, with the industrial isolates being the most sensitive.

SIGNIFICANCE AND IMPACT OF THE STUDY

The work shows that antibiotic/biocide correlations do occur, especially with clinical strains. That such correlations were not found with industrial isolates suggests that the clinical environment is responsible for the correlation. We could infer that it is the selective pressure of antibiotic usage that differentiates the clinical environment from the industrial.

The effect of interfering substances on the disinfection process: a mathematical model

AIMS

To gain a greater understanding of the effect of interfering substances on the efficacy of disinfection.

METHODS AND RESULTS

Current kinetic disinfection models were augmented by a term designed to quantify the deleterious effect of soils such as milk on the disinfection process of suspended organisms. The model was based on the assumption that inactivation by added soil occurred at a much faster rate than microbial inactivation. The new model, the fat-soil model, was also able to quantify the effect of changing the initial inoculum size (1 x 10(7)-5 x 10(7) ml(-1) of Staphylococcus aureus) on the outcome of the suspension tests. Addition of catalase to the disinfection of Escherichia coli by hydrogen peroxide, resulted in changes to the shape of the log survivor/time plots. These changes were modelled on the basis of changing biocide concentration commensurate with microbial inactivation.

CONCLUSIONS

The reduction in efficacy of a disinfectant in the presence of an interfering substance can be quantified through the use of adaptations to current disinfection models.

SIGNIFICANCE AND IMPACT OF THE STUDY

Understanding the effect of soil on disinfection efficacy allows us to understand the limitations of disinfectants and disinfection procedures. It also gives us a mechanism with which to investigate the soil tolerance of new biocides and formulations.

A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol

AIMS

The minimum inhibitory concentration (MIC) of oregano essential oil (OEO) and two of its principle components, i.e. thymol and carvacrol, against Pseudomonas aeruginosa and Staphylococcus aureus was assessed by using an innovative technique. The mechanism of action of the above substances was also investigated.

METHODS AND RESULTS

The applied technique uses 100-well microtitre plate and collects turbidimetric growth data. To produce the inhibition profiles, a wide range of concentrations were tested for each of the three compounds, as well as for carvacrol-thymol mixtures. Following a specific mathematical analysis of the observed inhibition profiles from all compounds, it was suggested that mixtures of carvacrol and thymol gave an additive effect and that the overall inhibition by OEO can be attributed mainly to the additive antimicrobial action of these two compounds. Addition of low amounts of each additive: (a) increased permeability of cells to the nuclear stain EB, (b) dissipated pH gradients as indicated by the CFDA-SE fluorescent probe irrespective of glucose availability and (c) caused leakage of inorganic ions.

CONCLUSION

Mixing carvacrol and thymol at proper amounts may exert the total inhibition that is evident by oregano essential oil. Such inhibition is due to damage in membrane integrity, which further affects pH homeostasis and equilibrium of inorganic ions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The knowledge of extent and mode of inhibition of specific compounds, which are present in plant extracts, may contribute to the successful application of such natural preservatives in foods, since certain combinations of carvacrol-thymol provide as high inhibition as oregano essential oil with a smaller flavour impact.

Advances in disinfection testing and modelling

AIMS

To develop a set of kinetic equations which more ably describe the disinfection process.

METHODS AND RESULTS

A group of functions, the fat equations, based on the model used for the quantification of microbial inhibition, was produced. These functions introduce a limit to the numbers of micro-organisms capable of being disinfected. These new expressions were shown to be more general forms of currently-used (e.g. log-linear) disinfection models, and accommodate the lags and/or tails of non-linear log-survivor--time plots. An advance in the experimental procedures used to obtain disinfection data, using an optical density technique, was developed concomitantly.

CONCLUSION

The methods of analyses (experimental and modelling) allow the researcher to examine, more ably, five-minute disinfection (or specific time disinfection tests) as well as the more important disinfection rate analyses.

SIGNIFICANCE AND IMPACT OF THE STUDY

The fat equations are an improvement over commonly-used rate models of disinfection, which are shown to be special cases of these equations. This raises the question as to whether our current understanding of the kinetic basis of disinfection requires revision.

Development of resistance to chlorhexidine diacetate in Pseudomonas aeruginosa and the effect of a "residual" concentration

Stable resistance in Pseudomonas aeruginosa NCIMB 10421 was obtained by step-wise exposure to gradually increasing concentrations of chlorhexidine diacetate (CHX). Repeated exposure to a proposed "residual" (sub-MIC) concentration of CHX also created stable resistance. Resistance was also developed by a single exposure to the "residual" concentration of CHX, but this was unstable. Similar experiments with Escherichia coli and CHX or cetylpyridinium chloride resulted in no significant increase in resistance. Antibiotic susceptibility profiles of the CHX-resistant P. aeruginosa cultures showed no cross-resistance, although some of the cultures were resistant to benzalkonium chloride.

Susceptibility testing: inoculum size dependency of inhibition using the Colworth MIC technique

The minimum inhibitory concentration, MIC, is an accepted and well used criterion for measuring the susceptibility of organisms to inhibitors. Many factors influence the MIC value obtained, including temperature, inoculum size and type of organism. A modification of the method developed in this laboratory to obtain inhibition profiles of antimicrobials was used to examine the effect of inoculum size on the degree of inhibition observed with respect to inhibitor concentration. The data obtained enabled the production of an empirical model of inhibition, based on a Gompertz function, relating the level of growth observed to both the inoculum size and concentration of the inhibitor. The inoculum size dependencies of phenethyl alcohol, phenoxyethanol, p-chloro-m-cresol, trichloro-phenol, thymol and dodecyltrimethylammmonium bromide against Staphylococcus aureus were obtained.

Susceptibility testing: accurate and reproducible minimum inhibitory concentration (MIC) and non-inhibitory concentration (NIC) values

Measuring the minimum inhibitory concentration (MIC) of a substance by current methods is straightforward, whereas obtaining useful comparative information from the tests can be more difficult. A simple technique and a method of data analysis are reported which give the experimentalist more useful information from susceptibility testing. This method makes use of a 100-well microtitre plate and the analysis uses all the growth information, obtained by turbidometry, from each and every well of the microtitre plate. A modified Gompertz function is used to fit the data, from which a more exact value can be obtained for the MIC. The technique also showed that at certain concentrations of inhibitor, there was no effect on growth relative to a control well (zero inhibitor). Above a threshold value, which has been termed the non-inhibitory concentration or NIC, growth becomes limiting until it reaches the MIC, where no growth relative to the control is observed.

Disinfection kinetics: a new hypothesis and model for the tailing of log-survivor/time curves

A new hypothesis for the understanding of chemical disinfection, which we have termed the Intrinsic Quenching hypothesis, is presented. This mechanistic treatment of disinfection kinetics is based on the hypothesis that the biocide concentration may not be in vast excess over the microbes, as is normally assumed. A mathematical model was developed and found to be useful in describing the observed kinetics of several disinfectants. The model suggested that the reason for the observation of non-linear, log-survivor curves was due to the ability of the microbes, in clean, soil-free conditions, to intrinsically quench the bulk concentration of biocide.

One explanation for the variability of the bacterial suspension test

Disinfection kinetic studies of sodium dodecyl sulphate, benzalkonium chloride and sodium hypochlorite against Staphylococcus aureus revealed that when a higher inoculum level of Staph. aureus than normal was used (approximately 1 log higher), the efficacy of disinfection was severely attenuated. Kinetic analysis using the Hom model for experiments carried out on tests using 3 x 108 organisms ml-1 were unable to account for the large increase in disinfection power observed when smaller inoculum levels were used. Since the inoculum was the same in every way except for the numbers used, the large variations in the log reduction/time curves could not be explained by a variation in the resistance of the population to the biocide, as identical log reduction-time curves should have resulted. The level of disinfection achieved for a given concentration of biocide was found to be approximately linearly related to the cell number ml-1 of test solution and not to the log number. The variation observed is believed to occur due to intrinsic self-quenching of the biocide by the microbes during the course of the disinfection test. As the level of free biocide decreases, the rate of reaction decreases, giving the tails of the log reduction/time curves. Such intrinsic self-quenching could explain the large variations known to occur in the legally required disinfection suspension tests.

A kinetic study of the effect of hydrogen peroxide and peracetic acid against Staphylococcus aureus and Pseudomonas aeruginosa using the bioscreen disinfection method

Hydrogen peroxide and peracetic acid at pH 4 were examined against Staphylococcus aureus and Pseudomonas aeruginosa using the published 'Bioscreen' technique of biocide analysis. The data were examined using either classical Chick-Watson (CW) log-linear disinfection kinetics or the empirical, non-linear time Hom model. In some cases, modelling the data with the classical CW method gave good linear correlations, in others, however, deviations from this model were observed. In such cases the Hom model proved an adequate descriptor of the data. The Bioscreen technique therefore gives data which can be analysed using the normal mechanistic and empirical models currently available.

An investigation into the differences between the Bioscreen and the traditional plate count disinfectant test methods

Investigations of biocide efficacy by automated methods involving optical density measurements, e.g. using the recently published 'Bioscreen' method, are complicated by the fact that a poor correlation often exists between the log reductions obtained using the automated method vs those obtained by the traditional plate count methods. It was hypothesized that the differences observed between the two methods were due to the level of cell injury, which was masked by the optical density methods but which was recognized by the plate counts. Comparisons of log reductions following a disinfection test always showed the Bioscreen method to be overestimating the log reductions with respect to the plate counts. A correlation between colony size on the plates and the 'Bioscreen' results for a fixed disinfectant concentration and contact time was found using Global Imaging software. The results obtained also suggested that the observed colony area was dependent on the amount of injury incurred by a microbe during the disinfection process. A mathematical model of injury was developed which predicted the observed differences between the Bioscreen and the traditional plate method. The model further suggested a possible reason for biocidal lags.

Experimental neodymium:YAG laser damage to acrylic, poly(methyl methacrylate), and silicone intraocular lens materials

PURPOSE

To compare neodymium:YAG (Nd:YAG) laser effects on acrylic, silicone, and poly(methyl methacrylate) (PMMA) intraocular lens (IOL) polymers.

METHODS

Ten Nd:YAG laser exposures were produced in each of 6 implantation-quality acrylic (Alcon MA60BM), silicone (Staar AQ1016), and PMMA (Alcon MC60BM) IOLs under identical conditions. Each polymer type was irradiated at 6 power settings (0.3, 0.5, 1.0, 1.5, 2.0, and 3.0 mJ) and at 2 focal points (midpoint of lens optic and on the posterior surface to which a cellophane membrane was affixed). The linear extent of the damage was measured using light microscopy. Specimens exposed to 1.0 mJ were processed for scanning electron microscopy.

RESULTS

The damage threshold (> or = 5 microns depth) was 0.3 mJ for silicone and 1.0 mJ for acrylic and PMMA IOLs. At the clinically relevant power levels, 1.0 to 2.0 mJ, the depth of damage in the acrylic polymer was 11.9 to 30.5 times less than the depth in the silicone polymer. Similarly, the depth of damage in the PMMA polymer was 5.4 to 52.6 times less than the depth in the silicone polymer. The morphologic pattern of damage in the silicone IOL showed a deep, irregularly configured trough with meandering tendrils. Acrylic IOL damage morphology consisted of an ameboid-shaped entry site without radiating fractures and mild posterior penetration. Poly(methyl methacrylate) IOL damage consisted of a shallow focal trough with radiating fractures.

CONCLUSIONS

The silicone IOL polymer had the lowest threshold for laser-induced damage and greater linear extension of damage than the PMMA and acrylic IOL polymers. Poly(methyl methacrylate) and silicone polymers exhibited collateral damage or ejected particulates adjacent to the entry site, whereas the acrylic polymer showed a discrete locus of damage.

Weak-acid preservatives: modelling microbial inhibition and response

Weak-acid preservatives are widely used to prevent microbial spoilage of acidic foods and beverages. Characteristically, weak-acid preservatives do not kill micro-organisms but inhibit growth, causing very extended lag phases. Preservatives are more effective at low pH values where solutions contain increased concentrations of undissociated acids. Inhibition by weak-acids involves rapid diffusion of undissociated molecules through the plasma membrane; dissociation of these molecules within cells liberates protons, thus acidifying the cytoplasm and preventing growth. By modelling preservative action in yeast, using a thermodynamic and kinetic approach, it was possible to demonstrate that: (i) inhibition depends more on the degree to which individual preservatives are concentrated within cells, rather than on undissociated acid concentration per se; (ii) it is entirely feasible for microbes to pump protons out of the cell during extended lag phase and raise internal pH (pHi), despite further influx of preservatives; (iii) the duration of the lag phase can be predicted from the model, using a Gaussian fit of proton-pumping H(+)-ATPase activity against pHi; (iv) theoretical ATP consumption for proton pumping can be directly correlated with the reduction in cell yield observed in glucose-limited cultures.

Intraocular lens changes after short- and long-term exposure to intraocular silicone oil. An in vivo study

OBJECTIVE

Silicone oil frequently is used as a vitreous substitute after complex vitreoretinal procedures. The authors sought to study the effect of short- and long-term exposure to silicone oil on polymethyl methacrylate (PMMA, MC60BM; Alcon, Ft. Worth, TX), silicone (SI-30NB; AMO, Irvine, CA), and soft acrylic (MA60BM; Alcon) intraocular lenses (IOLs).

DESIGN

An experimental animal study.

INTERVENTION

Forty-one New Zealand white rabbits underwent lensectomy, vitrectomy, capsulotomy, and placement of one of the three types of IOLs into the ciliary sulcus. All lenses were weighed before implantation and 24 hours after explanation. In the short-term study, an fluid-air exchange was performed followed by the use of silicone oil (1000 centistokes) to coat the posterior lens surface. Immediately thereafter, an air-fluid exchange was performed and the remaining silicone on the posterior lens surface was aspirated or wiped or both for 1 minute using a soft-tipped extrusion cannula for 1 minute. In the long-term study, the posterior segment was filled with 1000 centistokes silicone oil after fluid-air exchange. Animals were observed by slit-lamp biomicroscopy and photographed at 1 week, 1 month, and 3 months after surgery. At 3 months, all animals underwent silicone-fluid exchange, an attempt to manually remove any remaining silicone oil, and lens explanation.

RESULTS

In the short-term study, no silicone oil remained after manual wiping and/or aspiration in any of the four rabbits implanted with PMMA or acrylic IOLs. In the animals with silicone IOLs, a significant amount of silicone oil remained on the posterior lens surface of all lenses (P < 0.01 for silicone vs. acrylic and silicone vs. PMMA). No statistically significant difference was found when comparing the lens weights in each group before and after implantation. In the long-term study, aqueous droplet formation was found on the posterior lens surface of six of nine PMMA IOLs and ten of ten silicone IOLs at 3 months. No opacities were observed in the group with acrylic IOLs (P < 0.001 for acrylic vs. silicone, P = 0.0018 for acrylic vs. PMMA, and P = 0.047 for PMMA vs. silicone). Adherent silicone oil remained on two of nine PMMA IOLs and on none of ten acrylic IOLs. In contrast, a significant amount of silicone oil remained on the posterior lens surface of ten of ten silicone IOLs (P < 0.001 for silicone vs. acrylic and silicone vs. PMMA). Furthermore, there was a statistically significant increase in lens weights before and after implantation in the silicone IOL group but not in the PMMA or acrylic group (P < 0.01).

CONCLUSIONS

It is extremely difficult or impossible to remove remaining silicone oil from the posterior surface of a silicone IOL after short- or long-term exposure to silicone oil. This oil may interfere with the surgeon's view of the retina and may diminish the patient's visual acuity. In contrast, oil is readily removed from the posterior surface of an acrylic IOL. The authors therefore recommend the use of a soft acrylic or PMMA IOL over a silicone IOL when choosing a lens for implantation in patients who may require vitreoretinal procedures with silicone oil tamponade.

Viscoelastic adherence to corneal endothelium following phacoemulsification

PURPOSE

To compare the residual adherence of viscoelastics to the corneal endothelium following phacoemulsification in an in vitro rabbit model.

SETTING

Departments of Ophthalmology and Anatomy, Wayne State University, Detroit, Michigan, USA.

METHODS

Three groups of 10 rabbit eyes each had a lensectomy via phacoemulsification using sodium hyaluronate (Amvisc Plus, Healon GV) or sodium chondroitin sulfate-sodium hyaluronate (Viscoat) as the viscoelastic agent. After phacoemulsification and cortex removal, a central corneal block was excised, cryofixed, and processed for light and electron microscopy. Viscoelastic thickness was determined by a calibrated reticule on the light microscope or a calibrated measuring program in the electron microscope. The nonparametric statistical test, Kruskal-Wallis, was used to compare viscoelastic groups.

RESULTS

Median phacoemulsification time between viscoelastic agents was not significantly different. Median viscoelastic thicknesses were 13.0 microns for Amvisc Plus, 0.4 micron for Healon GV, and 375.0 microns for Viscoat. Each was significantly different from the others (Kruskal-Wallis, P < .001).

CONCLUSIONS

Median thickness of Amvisc Plus, Healon GV, and Viscoat remaining adherent to the corneal endothelium after phacoemulsification was markedly different. Viscoat provided the greatest amount of viscoelastic material adjacent to the corneal endothelium.

Disinfectant testing: use of the Bioscreen Microbiological Growth Analyser for laboratory biocide screening

A new method is described for screening potential biocides based on the traditional suspension test using the Bioscreen optical plate reader. This new method is rapid, reproducible, quantitative and cost effective. Data obtained by this new method are not directly equivalent to the log reduction normally quoted, but give a measurement of the total effect of the biocide on the microbe population, measuring the effect of injury as well as death (non-viability). The method allows for the routine examination of disinfection kinetics, the study of which leads to greater scientific insight into disinfection than that achieved by the standard 5 min, one-point, disinfection tests currently employed.

Incision sizes for foldable intraocular lenses

OBJECTIVE

The purpose of the study is to determine the minimal incision sizes required for implantation of a variety of different foldable intraocular lenses (IOLs) and to evaluate the effect of incision size on tissue damage.

DESIGN

Randomized experimental study.

PARTICIPANTS

Sixty-nine fresh human cadaveric eyes: 15 (pilot study), 48 (main study), and 6 (scanning electron microscopy study).

INTERVENTION

Implantation of foldable IOLs into cadaveric eyes.

MAIN OUTCOME MEASURES

In 48 fresh human cadaveric eyes, limbal corneal tunnel incisions were made, and in a randomized fashion, 8 different foldable IOLs of 20.5 diopters (D) were inserted: 4 silicone (SI-30NB, Allergan Medical Optics, Irvine, CA; C10UB, Chiron Ophthalmics, Inc, Irvine, CA; LI41U, IOLAB, Chiron Ophthalmics, Inc, Irvine, CA; AA-4203, Staar Surgical Company, Monrovia, CA); two soft acrylic (MA60BM and MA30BA, both Alcon Laboratories, Inc, Ft. Worth, TX); and two hydrogel models (SH30BC, Alcon; H60M, Storz Ophthalmics, Inc, St. Louis, MO). For each IOL model, six insertions were performed with a recommended implantation device. Using calipers, the authors measured internal and external incision sizes before and after insertion. Scanning electron microscopy was performed on selected incisions in six additional human cadaveric eyes.

RESULTS

Incision sizes after insertion ranged from 3.2 to 3.8 mm. The smallest incisions permitting IOL insertion were associated with the injectors. However, these incisions enlarged after insertion by approximately 11% and then were similar to the incision sizes after forceps insertion of the high-refractive-index silicone, the 5.5-mm optic acrylic, and the one-piece hydrogel IOL. The largest incisions were associated with the 6-mm acrylic IOL and the three-piece silicone IOL with a lower refractive index. The scanning electron microscopy showed tearing of corneal tissue after implantation through the smallest incision; this was more pronounced with injectors than with forceps.

CONCLUSIONS

Corneal tunnel incisions enlarged up to 11% after insertion of foldable IOLs through the smallest possible incision. With current technology, the smallest postinsertion incision size of a 20.5-D foldable IOL is 3.2 mm.

Change in ribosomal DNA spacer-length composition in maize recurrent selection populations. 2. Analysis of BS10, BS11, RBS10, and RSSSC

Four maize (Zea mays L.) populations selected for grain yield (BS10, Iowa Two-ear Synthetic; BS11, formerly Pioneer Two-ear Composite; RBS10, Illinois strain of BS10; and RSSSC, Illinois strain of Iowa Stiff Stalk Synthetic) were assayed for molecular variation in the ribosomal DNA (rDNA) intergenic spacer (IGS) at initial and advanced cycles of selection. RSSSC and RBS10 underwent reciprocal recurrent selection with an inbred tester in a high-yield environment, whereas BS10 and BS11 were subjected to full-sib reciprocal recurrent selection. Maize rDNA, which encodes the ribosomal RNA genes, is highly repetitive and shows IGS length variation within and among individuals. Five different ribosomal spacer-length variants (rslvs) and a polymorphic SstI restriction site in the IGS were detected in the four populations. The five rslvs and the polymorphic restriction fragment were observed in 20 different combinations or hybridization fragment patterns (HP). RSSSC, RBS10, and BS11 showed significant changes in the overall rslv and HP frequencies between cycle 0 and the advanced cycle of selection, whereas BS10 did not. In general, two specific HPs were more frequent in the majority of the advanced cycles of the four populations. The frequency changes between initial and advanced cycles were more dramatic for HPs than rslvs. These results are consistent with earlier findings and further support the hypothesis that certain rDNA HPs and/or linked loci may be responding to selection for grain yield and may be associated with a selective advantage in US Corn Belt environments.

Monitoring local food security and coping strategies: lessons from information collection and analysis in Mopti, Mali

Save the Children Fund (UK) established a local food security monitoring project in the Mopti region of Mali, which was operational between 1987 and 1993. This article describes some of the lessons learnt from this experience of monitoring food security and coping strategies. It illustrates how coping strategies can be an important element in tracking vulnerability in the Sahel, but that interpretation is complex and there are limitations to their use. Secondly, consideration must be given to the institutional context in which information systems are set up. Information providers must be linked institutionally to response mechanisms, to ensure that data are fed systematically into the design, implementation and monitoring of appropriate response.

Evaluation of a superactivated charcoal paste and detergent and water in prevention of T-2 toxin-induced local cutaneous effects in topically exposed swine

T-2 toxin (6 mg) dissolved in 90% DMSO was topically applied to nine 9-cm2 sites on the dorsum of each of nine young, crossbred, specific pathogen-free, female pigs, 20.6 +/- 1.9 kg in weight. A superactive charcoal paste (SAC) and/or a soap-and-water wash (SOAP) was applied to eight of the T-2-exposed sites on each animal. These treatments were applied at various times postexposure ranging from 5 to 65 min. The site that received T-2 alone served as a positive control. DMSO was applied to a tenth site on each pig as a negative control. Animals were killed 1, 3, or 6 days after treatment. Skin lesions were examined and graded grossly and histologically. No adverse systemic clinical signs were observed in any of the animals. Marked reddening and slight swelling of the T-2 toxin-treated positive control sites were present throughout the study. Ulceration of this site was first noted on Day 3. All therapeutic regimens effectively reduced lesion severity resulting from T-2 toxin application. Significant differences in relative effectiveness were also seen between treatments. In each significant pair, the ordering of mean lesion severity was SAC/SOAP less than SAC or SOAP and SOAP less than SAC. As a single treatment, SOAP appears to be more effective than SAC in reducing lesion severity. These results failed to provide unequivocal evidence of an additive therapeutic effect when SAC and SOAP were used sequentially on the same site.

Experimental T-2 toxicosis in swine following inhalation exposure: clinical signs and effects on hematology, serum biochemistry, and immune response

Nine- to ten-week-old, male castrated, specific pathogen-free derived pigs, weighing 34 to 42 kg, were exposed to a T-2 toxin aerosol (390 micrograms/liter, 1.5 microM mass median aerodynamic diameter) for a time period which allowed an amount equivalent to 8 mg/kg to be nebulized (six pigs). Control animals (five pigs) were exposed to an equivalent amount of the nebulized vehicle. Pigs were immunized subcutaneously with sheep red blood cells on Days 0 and 21. Whole blood and serum samples were taken periodically for clinical pathologic and immunologic studies. Pigs were closely observed, and daily rectal temperatures and weekly weights were measured. The T-2-treated pigs vomited and exhibited cyanosis, anorexia, lethargy, lateral recumbency, slightly elevated rectal temperature, and depressed body weight gain. The lymphocyte count decreased while the neutrophil count increased. The concentrations of total serum protein and hemoglobin declined. There was a marked increase in serum alkaline phosphatase activity on Day 1, followed by a marked and persistent decrease. Mitogen-induced (Con A, PHA, and PWM) blastogenic responses of peripheral blood mononuclear cells and hemagglutination titers to SRBC were also transiently decreased. Thus, inhalation exposure of pigs to a sublethal dose of T-2 toxin caused clinical signs of toxicity and adverse effects on clinical pathologic parameters and immune responses; however, most of these effects were short-lived. The changes described in our study resemble those reported in pigs given T-2 toxin by intravascular injection.

The efficacy of superactivated charcoal in treating rats exposed to a lethal oral dose of potassium cyanide

Due to the apparent low binding capacity of activated charcoal for potassium cyanide (KCN) in vitro, the use of oral activated charcoal therapy for oral exposure to cyanide compounds is controversial. In our study, rats were given a lethal oral dose of ground granular KCN (35 or 40 mg/kg) in a gelatin capsule followed immediately by either 4 g/kg of superactivated charcoal in a 20% suspension or a similar volume of deionized water. Signs of cyanide toxicosis occurred rapidly, with a mean time to signs of 3.3 and 2.7 minutes in control animals receiving 35 or 40 mg/kg KCN, respectively. All 26 of the control rats showed signs, and all but one in the 35 mg/kg group died within 19 minutes. Only 12 of 26 rats treated with superactivated charcoal showed signs of KCN toxicosis and eight of those animals died. Oral exposure of rats to lethal doses of KCN can be treated effectively by immediate administration of superactivated charcoal.

Experimental T-2 toxicosis in swine following inhalation exposure: effects on pulmonary and systemic immunity, and morphologic changes

Thirty-four, 9- to 11-week-old, male castrated, crossbred, specific pathogen-free derived pigs were exposed to a T-2 toxin aerosol at a nebulized dose of 0 or 9 mg/kg in pairs, each pair consisting of 1 control and 1 T-2 treated pig which were exposed on the same day. Twenty to 30% of the toxin (1.8 to 2.7 mg/kg) was retained by the pigs. Five pairs were killed on each of 1, 3 and 7 days after dosing. Two pairs of pigs were designated as a 0.33-day group when one T-2 treated pig died and the other was killed in a moribund state at 8 to 10 hours after dosing. The pulmonary and systemic immunity and morphologic changes of the lungs and other organs were examined. Bronchoalveolar lavage was performed to obtain alveolar macrophages (AM) and pulmonary lymphocytes (PL). The phagocytic ability of AM and mitogen-induced blastogenic responses of enriched PL and peripheral blood lymphocytes were evaluated. Clinically, all of the T-2 treated pigs vomited and were cyanotic, anorexic, lethargic and laterally recumbent. In the 0.33-, 1-, and 3-day T-2 treated pigs, there was a marked reduction in AM phagocytosis and mitogen-induced blastogenic responses of PL but not of peripheral blood lymphocytes. Mild to moderate, multifocal interstitial pneumonia was seen in the majority of the T-2 treated pigs. In pigs dying following inhalation of T-2 toxin, there was a more severe pneumonia, as well as marked necrosis of lymphoid tissues, severe necrohemorrhagic gastroenteritis and edema of the gall bladder wall, and multifocal necrosis of the heart and pancreas. Thus, inhalation exposure to T-2 toxin can result in clinical signs and morphologic changes resembling those reported previously in pigs given T-2 toxin intravascularly (iv) at a dose of 1.2 mg/kg (approximate LD50) or greater, as well as death. Mild pulmonary injury as well as transient impairment of pulmonary immunity was present in pigs surviving inhalation exposure.

Therapeutic efficacy of superactive charcoal in rats exposed to oral lethal doses of T-2 toxin

Superactive charcoal, a compound known to complex with many toxins, was evaluated in this study for its effectiveness in preventing death in rats given an oral lethal dose of 8 mg/kg body weight of T-2 toxin. The median effective dose of oral superactive charcoal in preventing deaths in rats was 0.175 g/kg body weight. Concurrent use of cathartics, such as sorbitol, magnesium sulfate and sodium sulfate, to facilitate removal of the superactive charcoal:T-2 toxin complex formed in vivo did not enhance the survival rates of rats. One gram per kilogram body weight oral superactive charcoal enhanced survival times and survival rates in rats given 8 mg/kg of T-2 toxin as late as 3 hr after the T-2 toxin was administered. Some benefit in survival rate may be derived from giving the superactive charcoal as late as 5 hr after the T-2 toxin.

Plant factors controlling seed set in maize : the influence of silk, pollen, and ear-leaf water status and tassel heat treatment at pollination

In maize (Zea mays L.) large decreases in kernel number result when low water potentials (Psi(w)) and high temperatures occur during pollination. To gain insight into the basis for the decreased seed set, silk, pollen, and ear-leaf Psi(w), the capability for silk osmotic adjustment, and pollen appearance were measured to determine their relationship to seed set. A multiple-eared or prolific (high carbohydrate availability to the pistillate inflorescence) hybrid (B73 x FR25), a heat sensitive hybrid (WF9 x A632), and a commercial hybrid (B73 x Mo17) were studied. A cross-pollination experiment, with pollination limited by pollen amount, was conducted to determine the impact on seed set of water and heat stressing the tassel and water stressing the ear. At low Psi(w), silk Psi(w) and seed set were decreased whereas pollen Psi(w), appearance, and viability were unaffected. High temperature resulted in a 2 megapascal decrease in pollen Psi(w), visually damaged pollen being shed, decreased pollen viability, and, in two of the hybrids, substantially decreased pollen shed. Prolificacy did not result in increased silk solute accumulation but did result in superior seed production by the pistillate inflorescence at low Psi(w). The magnitude of the decrease in silk solute potential was small (0.2 megapascal) and similar for all genotypes. One hybrid maintained a relatively high silk turgor but this hybrid also decreased the most in seed production when the pistillate inflorescence was water deficient. These results indicated an adverse effect of high temperature on pollen development, a positive relationship between seed production and silk water status, and no advantage to high silk turgor after silk emergence in maintaining seed production. Additionally, there was no evidence of variation in silk solute regulation capability among hybrids which varied in prolificacy, a trait important in drought tolerance, but the seed production of the pistillate inflorescence of the prolific hybrid was least affected by water deficit.

Systemic distribution of blood flow during T-2 toxin induced shock in swine

Three groups of swine (6 per group) were used to determine hemodynamic and blood flow alterations induced by T-2 toxin. Two groups were dosed at 0.6 or 2.4 mg/kg T-2 toxin, and one group served as a vehicle control (70% ethanol). Organ blood flow was determined at 0 hr (predosing) and at 90-min intervals for 6 hr postdosing using 15-micron diameter radionuclide labeled microspheres injected into the left atrium. Hemodynamic parameters were obtained at the same time points. The infusion of T-2 toxin resulted in reductions in cardiac output. This trend appeared to reverse itself in the low dose animals after 3 hr, whereas in the high dose group, cardiac output continued to decline. Mean aortic pressure (MAP) declined in a dose dependent fashion which tended to parallel the reduction observed in cardiac output. Heart rate was increased in both groups treated with T-2 toxin. Blood flow, to the brain, heart, and kidneys decreased following exposure to the toxin. The relative percentage of cardiac output received by these organs, however, was maintained despite the drop in blood flow. Pancreatic and splenic blood flows were the most severely compromised as a result of T-2 toxicosis. Consequently, the percentage of cardiac output going to the pancreas and spleen was dramatically reduced. Adrenal, hepatic, and total gastrointestinal blood flows increased or did not change from control values. As a result, the percentage of cardiac output supplying these organs increased.

Interaction of carbon and nitrogen metabolism in the productivity of maize

Five maize (Zea mays L.) hybrids, FS854, B73 x Mo17, B84 x Mo17, B73 x B77, and P3382, grown under field conditions, were sampled at intervals during the grain-filling period. Plants were subdivided into stalks (including sheaths), leaves, and kernels. These parts were assayed for dry weight, reduced nitrogen, and extractable nonstructural carbohydrates. The duration and rates of net nitrate reduction and photosynthesis were approximated by the changes over time in the accumulation of reduced nitrogen and dry weight by the plant (total, above ground), respectively.Data on the accumulation of reduced nitrogen and dry weight by the plant show that decreases in nitrate reduction preceded (in time and extent for four of the hybrids and in extent for FS854) decreases or cessation of photosynthesis. FS854 continued to accumulate reduced nitrogen and dry matter throughout the grain-filling period.The patterns of change in stalk carbohydrate and reduced nitrogen during the early stages of ear development show the stalk serves as a storage reservoir and that these reserves were remobilized during the final stages of grain development. The marked increase and maintenance of dry weight and carbohydrate content of stalks until 34 days after anthesis, shows the capacity of the leaves to produce photosynthate through the first half of the grain-filling period exceeds the needs of the ear and/or the transport system. In contrast, stalk nitrogen content shows a slight increase up to 12 days after anthesis and decreases continually thereafter. Leaf nitrogen was lost continuously throughout grain development. The potential capacity of the plant to supply newly reduced nitrogen was inadequate to support initiation and early development of the kernels without remobilization of vegetative nitrogen. Of the two hybrids having delayed leaf senescence, FS854 with its initially higher concentration and content of reduced nitrogen in the stalk, initiated and developed a bigger ear than P3382, which had lower levels of stalk nitrogen.Three of the five hybrids had ;near linear' rates of accumulation of kernel dry weight, whereas none of the hybrids had linear rates of gain in kernel nitrogen. All hybrids had maximum or near maximum rates of gain of kernel nitrogen between 26 and 34 days after anthesis and a marked reduction (41-52%) of rates in the following sampling interval. These decreases are concurrent with decreases in rates of nitrate reduction (nitrogen accumulation) by the whole plant for four of the hybrids and with decreases in remobilization of nitrogen from the vegetation of FS854. Data for the ratio of rates of accumulation of dry weight/reduced nitrogen by the kernels versus time after anthesis, show that the accumulation of dry weight and reduced nitrogen are independent of each other. The variations in the ratio values appear best related to variations in the availability of nitrogen from the vegetation.

Chromosome pairing within genomes in maize-Tripsacum hybrids

When the ten chromosomes of maize were inserted inlto a polyploid (2n = 72) Tripsacum dactyloides background they formed up to five pairs at meiosis. Two plants that each contained 36 Tripsacum and 14 maize chromosomes were deprived from the F(1) of maize x Tripsacum. Chromo. somes of these plants frequently formed 25 bivalents, 18 between Tripsacum chromosomes and seven between maize chromosomes. Maize chromosomes could be distinguished from Tripsacum chromosomes on the basis of size. The withint-genome pairing is probably induced by the genetic background.

Inheritance of nitrate reductase activity in Zea mays L

Since the F(1) hybrid (B14 x Oh43) had been shown to have a higher (heterotic) level of nitrate reductase activity than either inbred parent (B14 or Oh43), studies were undertaken to determine the mode of inheritance. Standard methods for determining Mendelian inheritance were used to study segregation for level of nitrate reductase activity of individual plants. The genetic material used was the inbreds B14 and Oh43, F(1), F(1) backcrossed to both parents, F(2), F(3), and F(4) generations of the cross B14 x Oh43. The plant material was grown in the field and in growth chambers. It was shown that the maize inbreds B14 and Oh43 differ at two loci that control the level of nitrate reductase activity. Each inbred is homozygous for a dominant or partially dominant allele at one locus and homozygous recessive at a second locus. The locus at which B14 carries a dominant allele carries the recessive allele in Oh43. Oh43 has both a higher in vivo rate of synthesis of nitrate reductase and higher in vivo and in vitro loss of enzyme activity (decay) than B14. Thus, the rates of both enzyme synthesis and decay are factors governing the level of nitrate reductase activity in corn. The data suggest that the heterotic level of nitrate reductase activity in the F(1) hybrid is the result of inheritance of qualities that gives it "intermediate" rates of enzyme synthesis and decay.