An Improved Detached-Leaf Assay for Phenotyping Net Blotch of Barley Caused by Pyrenophora teres

Net blotch, caused by Pyrenophora teres, is a major barley (Hordeum vulgare) leaf disease worldwide. P. teres occurs as two forms-P. teres f. teres, and P. teres f. maculata-inducing net and spot-like symptoms, respectively. An intact-seedling assay, where entire seedlings are inoculated by spraying with a conidial suspension, is frequently used for phenotyping net blotch. However, this presents a biosecurity risk in the glasshouse when nonlocal isolates are being screened. Alternatively, a detached-leaf assay (DLA-droplet method) can be used in which leaf segments laid out in a covered tray are inoculated with droplets of a conidial suspension, confining the inoculum. However, using this method, net and spot form symptoms cannot be distinguished from each other. We have developed an improved DLA (DLA-spray method) in which detached whole leaves are sprayed with the inoculum to produce distinct lesions. We compare the results for the three phenotyping methods above using four isolates from both net and spot forms of the disease to inoculate a standard set of eight barley genotypes. Results indicate that the DLA-spray method is a functional, informative and rapid test that readily differentiates the two forms of the pathogen in a biosecure environment.

Assessment of Fusarium pseudograminearum and F. culmorum Biomass in Seedlings of Potential Host Cereal Species

Fusarium crown rot is a major disease of wheat and barley worldwide, with the most frequently isolated causal agents being Fusarium pseudograminearum and F. culmorum. This study has successfully designed a quantitative polymerase chain reaction assay that is specific for F. culmorum, which has been used in conjunction with a previously established F. pseudograminearum-specific assay to compare the location and extent of infection by each fungus across a range of potential hosts, including six winter and three summer cereal species. All common winter cereals, excluding oat, demonstrated a similar range of visual and fungal biomass results when inoculated with either F. pseudograminearum or F. culmorum. Oat exhibited the lowest visual disease ratings and fungal biomass values of the winter cereals, while the sorghum, maize, and rice cultivars returned the lowest values overall. The ranking of host species according to visual discoloration was strongly correlated for both pathogens. Visual reactions to F. pseudograminearum were greater than those caused by F. culmorum in all potential hosts trialed; however, fungal biomass results only indicated this trend for barley. These results demonstrate significant variation in the ability of these pathogens to colonize the range of cereal species examined and also suggest differences between the pathogens in their patterns of host colonization.

Colonization of Durum Wheat (Triticum turgidum L. var. durum) Culms Exhibiting Premature Senescence (Dead Heads) Associated with Fusarium pseudograminearum Crown Rot

Fusarium crown rot is a significant disease of durum wheat (Triticum turgidum L. var. durum), which exhibits high levels of disease susceptibility. The most extreme symptom of crown rot is a prematurely senescing culm that typically fails to set grain. Individual crown rot-affected durum wheat plants displaying both nonsenescent and prematurely senescent culms were harvested to compare visual discoloration, Fusarium pseudograminearum biomass, and vascular colonization in culm sections sampled at three different heights above the crown. Field samples of EGA Bellaroi were collected at Wellcamp, QLD, in 2011, 2012, 2013, and 2014, and of Hyperno at Narrabri, NSW, in 2014. Prematurely senescent culms exhibited greater visual discoloration, F. pseudograminearum biomass, and vascular colonization than nonsenescent culms in each year they were examined. The extent of these differences varied between environments and timing of collection in each year. Vascular colonization initially occurred in xylem vessels and spread into phloem tissues as disease severity increased. The increased presence of hyphae in vascular bundles of prematurely senescing culms provides strong evidence for the hypothesis that restriction of water and nutrient movement in a diseased culm is a key factor in crown rot severity.

Rare Pyrenophora teres Hybridization Events Revealed by Development of Sequence-Specific PCR Markers

Pyrenophora teres f. teres and P. teres f. maculata cause net form and spot form, respectively, of net blotch on barley (Hordeum vulgare). The two forms reproduce sexually, producing hybrids with genetic and pathogenic variability. Phenotypic identification of hybrids is challenging because lesions induced by hybrids on host plants resemble lesions induced by either P. teres f. teres or P. teres f. maculata. In this study, 12 sequence-specific polymerase chain reaction markers were developed based on expressed regions spread across the genome. The primers were validated using 210 P. teres isolates, 2 putative field hybrids (WAC10721 and SNB172), 50 laboratory-produced hybrids, and 7 isolates collected from barley grass (H. leporinum). The sequence-specific markers confirmed isolate WAC10721 as a hybrid. Only four P. teres f. teres markers amplified on DNA of barley grass isolates. Amplified fragment length polymorphism markers suggested that P. teres barley grass isolates are genetically different from P. teres barley isolates and that the second putative hybrid (SNB172) is a barley grass isolate. We developed a suite of markers which clearly distinguish the two forms of P. teres and enable unambiguous identification of hybrids.

Pentaploid Wheat Hybrids: Applications, Characterisation, and Challenges

Interspecific hybridisation between hexaploid and tetraploid wheat species leads to the development of F1 pentaploid hybrids with unique chromosomal constitutions. Pentaploid hybrids derived from bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum spp. durum Desf.) crosses can improve the genetic background of either parent by transferring traits of interest. The genetic variability derived from bread and durum wheat and transferred into pentaploid hybrids has the potential to improve disease resistance, abiotic tolerance, and grain quality, and to enhance agronomic characters. Nonetheless, pentaploid wheat hybrids have not been fully exploited in breeding programs aimed at improving crops. There are several potential barriers for efficient pentaploid wheat production, such as low pollen compatibility, poor seed set, failed seedling establishment, and frequent sterility in F1 hybrids. However, most of the barriers can be overcome by careful selection of the parental genotypes and by employing the higher ploidy level genotype as the maternal parent. In this review, we summarize the current research on pentaploid wheat hybrids and analyze the advantages and pitfalls of current methods used to assess pentaploid-derived lines. Furthermore, we discuss current and potential applications in commercial breeding programs and future directions for research into pentaploid wheat.

Histopathological Assessment of Fusarium pseudograminearum Colonization of Cereal Culms During Crown Rot Infections

Histopathological assessment of the crown rot pathogen Fusarium pseudograminearum was performed using fluorescence microscopy of culm tissues of six cereal genotypes grown in inoculated field conditions. Tissue samples were collected at 10, 16, and 22 weeks after planting (WAP). Colonization of culm tissues was initiated through epidermal penetration, most distinctly through stomatal apertures, and progressed into the parenchymatous hypoderm, which exhibited the discoloration used as the basis for visual assessment of disease. Hyphae spread from the culm base vertically through the tissues, initially via the hypoderm and pith cavity. Colonization of sclerified cells occurred later in the disease process. Both xylem and phloem tissues became colonized by 16 WAP in all host genotypes, with colonization being less extensive in the more resistant genotypes. Culms displaying dead head symptoms revealed dense colonization in at least the first three internodes, with frequent xylem vessel and phloem cell occlusions. Paired living culms from the same plants exhibited less extensive colonization. These observations have revealed the ability of F. pseudograminearum to colonize all cell types of nodal and internodal sections, including vascular tissues, across all host genotypes. This study is the first detailed examination of the pattern of F. pseudograminearum colonization in adult hosts and indicates a potential vascular mechanism by which the effects of crown rot are produced.

Post-head-emergence frost in wheat and barley: defining the problem, assessing the damage, and identifying resistance

Radiant frost is a significant production constraint to wheat (Triticum aestivum) and barley (Hordeum vulgare), particularly in regions where spring-habit cereals are grown through winter, maturing in spring. However, damage to winter-habit cereals in reproductive stages is also reported. Crops are particularly susceptible to frost once awns or spikes emerge from the protection of the flag leaf sheath. Post-head-emergence frost (PHEF) is a problem distinct from other cold-mediated production constraints. To date, useful increased PHEF resistance in cereals has not been identified. Given the renewed interest in reproductive frost damage in cereals, it is timely to review the problem. Here we update the extent and impacts of PHEF and document current management options to combat this challenge. We clarify terminology useful for discussing PHEF in relation to chilling and other freezing stresses. We discuss problems characterizing radiant frost, the environmental conditions leading to PHEF damage, and the effects of frost at different growth stages. PHEF resistant cultivars would be highly desirable, to both reduce the incidence of direct frost damage and to allow the timing of crop maturity to be managed to maximize yield potential. A framework of potential adaptation mechanisms is outlined. Clarification of these critical issues will sharpen research focus, improving opportunities to identify genetic sources for improved PHEF resistance.

Markers for seedling and adult plant crown rot resistance in four partially resistant bread wheat sources

QTL identified for seedling and adult plant crown rot resistance in four partially resistant hexaploid wheat sources. PCR-based markers identified for use in marker-assisted selection. Crown rot, caused by Fusarium pseudograminearum, is an important disease of wheat in many wheat-growing regions globally. Complete resistance to infection by F. pseudograminearum has not been observed in a wheat host, but germplasm with partial resistance to this pathogen has been identified. The partially resistant wheat hexaploid germplasm sources 2-49, Sunco, IRN497 and CPI133817 were investigated in both seedling and adult plant field trials to identify markers associated with the resistance which could be used in marker-assisted selection programs. Thirteen different quantitative trait loci (QTL) conditioning crown rot resistance were identified in the four different sources. Some QTL were only observed in seedling trials whereas others appeared to be adult plant specific. For example while the QTL on chromosomes 1AS, 1BS, and 4BS contributed by 2-49 and on 2BS contributed by Sunco were detected in both seedling and field trials, the QTL on 1DL present in 2-49 and the QTL on 3BL in IRN497 were only detected in seedling trials. Genetic correlations between field trials of the same population were strong, as were correlations between seedling trials of the same population. Low to moderate correlations were observed between seedling and field trials. Flanking markers, most of which are less than 10 cM apart, have now been identified for each of the regions associated with crown rot resistance.

Assessment of Infection by Fusarium pseudograminearum in Wheat Seedling Tissues Using Quantitative PCR and a Visual Discoloration Scale

Assessment among cereal genotypes of relative seedling resistance to the crown rot pathogen Fusarium pseudograminearum has been primarily based on visual discoloration of the leaf sheaths. This study is the first to investigate the relationship between the widely used visual rating of seedling leaf sheath discoloration and the degree of colonization of these tissues by the pathogen, based on quantitative polymerase chain reaction (qPCR) of fungal DNA using primers specific for the translation elongation factor α sequence. Fourteen-day-old seedlings of four hard white spring wheat genotypes which differ in their degree of resistance to the pathogen, based on the expression of visible symptoms, were inoculated using a droplet method and assessed weekly from 7 to 35 days after inoculation (dai) for both discoloration and fungal DNA content per unit of tissue weight. Both visual assessment of disease symptoms and qPCR of fungal biomass indicated significant differences between the partially resistant and susceptible wheat genotypes from 14 dai. Visual discoloration of leaf sheath tissues was strongly correlated with fungal biomass estimated by qPCR in all four genotypes; however, this correlation became weaker with increasing time after inoculation. Significant correlations between these parameters were indicated at 14, 21, and 28 dai whereas, by 35 dai, the correlation was not significant. Evaluation of plants at 14 dai provided a rapid test which gave clear discrimination between lines for both parameters and was the time point of closest correlation between fungal colonization and disease symptoms. Symptom expression at all times following inoculation was accompanied by tissue infection, and at no time was symptomless infection observed under this screening environment. These qPCR results confirm that visual assessments of disease symptoms reflect the extent of tissue colonization by the pathogen in recently colonized tissues and confirm the validity of visual assessments for disease rating in high-throughput screening of breeding materials.

Current and emerging screening methods to identify post-head-emergence frost adaptation in wheat and barley

Cereal crops can suffer substantial damage if frosts occur at heading. Identification of post-head-emergence frost (PHEF) resistance in cereals poses a number of unique and difficult challenges. Many decades of research have failed to identify genotypes with PHEF resistance that could offer economically significant benefit to growers. Research and breeding gains have been limited by the available screening systems. Using traditional frost screening systems, genotypes that escape frost injury in trials due to spatial temperature differences and/or small differences in phenology can be misidentified as resistant. We believe that by improving techniques to minimize frost escapes, such 'false-positive' results can be confidently identified and eliminated. Artificial freezing chambers or manipulated natural frost treatments offer many potential advantages but are not yet at the stage where they can be reliably used for frost screening in breeding programmes. Here we describe the development of a novel photoperiod gradient method (PGM) that facilitates screening of genotypes of different phenology under natural field frosts at matched developmental stages. By identifying frost escapes and increasing the efficiency of field screening, the PGM ensures that research effort can be focused on finding genotypes with improved PHEF resistance. To maximize the likelihood of identifying PHEF resistance, we propose that the PGM form part of an integrated strategy to (i) source germplasm;(ii) facilitate high throughput screening; and (iii) permit detailed validation. PGM may also be useful in other studies where either a range of developmental stages and/or synchronized development are desired.

Pyramiding QTL increases seedling resistance to crown rot (Fusarium pseudograminearum) of wheat (Triticum aestivum)

Crown rot of wheat (Triticum aestivum), predominantly caused by the fungus Fusarium pseudograminearum, has become an increasingly important disease constraint in many winter cereal production regions in Australia. Our group has previously identified a range of quantitative trait loci (QTL) for partial resistance to crown rot in various bread wheat sources. Here, we report on work that has assessed the effectiveness of pyramiding QTL to improve resistance to crown rot. Two doubled haploid populations were analysed--one from a cross between two previously characterised sources of partial seedling resistance (2-49 and W21MMT70; n = 208) and one from a cross between 2-49 and the commercial variety Sunco, a source of adult field resistance (n = 134). Both populations were phenotyped for seedling resistance to crown rot. Microsatellite and DArT markers were used to construct whole genome linkage maps for use in composite interval mapping (CIM) to identify QTL. Three QTL were detected in both trials conducted on the 2-49/W21MMT70 population. These were located on chromosomes 1D (QCr.usq-1D.1), 3B (QCr.usq-3B.1) and 7A. QCr.usq-1D.1 and the previously undetected 7A QTL were inherited from 2-49. QCr.usq-3B.1, inherited from W21MMT70, was the most significant of the QTL, explaining up to 40.5% of the phenotypic variance. Three QTL were identified in multiple trials of the Sunco/2-49 population. These were located on chromosomes 1D (QCr.usq-1D.1), 2B (QCr.usq-2B.2) and 4B (QCr.usq-4B.1). Only QCr.usq-2B.2 was inherited from Sunco. QCr.usq-4B.1 was the most significant of these QTL, explaining up to 19.1% of the phenotypic variance. In the 2-49/W21MMT70 population, several DH lines performed significantly better than either parent, with the best recording an average disease severity rating of only 3.8% of that scored by the susceptible check cultivar Puseas. These lines represent a new level of seedling crown rot resistance in wheat.

The use of high resolution melting (HRM) to map single nucleotide polymorphism markers linked to a covered smut resistance gene in barley

Using an established genetic map, a single gene conditioning covered smut resistance, Ruh.7H, was mapped to the telomere region of chromosome 7HS in an Alexis/Sloop doubled haploid barley population. The closest marker to Ruh.7H, abg704 was 7.5 cM away. Thirteen loci on the distal end of 7HS with potential to contain single nucleotide polymorphisms (SNPs) were identified by applying a comparative genomics approach using rice sequence data. Of these, one locus produced polymorphic co-dominant bands of different size while two further loci contained SNPs that were identified using the recently developed high resolution melting (HRM) technique. Two of these markers flanked Ruh.7H with the proximal marker located 3.8 cM and the distal marker 2.7 cM away. This is the first report on the application of the HRM technique to SNP detection and to rapid scoring of known cleaved amplified polymorphic sequence (CAPS) markers in plants. This simple, precise post-PCR technique should find widespread use in the fine-mapping of genetic regions of interest in complex cereal and other plant genomes.

Production of reactive oxygen species during non-specific elicitation, non-host resistance and field resistance expression in cultured tobacco cells

We examined production of reactive oxygen species (ROS) and induction of cell death in tissue-cultured tobacco cells undergoing different disease resistance responses. A superoxide-dependent hypersensitive response occurs during both the race-specific resistance response of tobacco cells challenged with incompatible zoospores of Phytophthora nicotianae and during non-specific elicitation of tobacco cells challenged with Phytophthora glucan elicitors extracted from the fungal cell wall. Inhibition studies are consistent with dependence upon endogenous Ca²⁺ levels, and with involvement of NAD(P)H oxidase and peroxidases in production of ROS during both specific and non-specific elicitation. The patterns of resistance expression during non-host resistance or field resistance responses appear to be similar to race-specific resistance expression with regard to the timing and order of events. However, the intensity of the response is very much reduced. In contrast, during non-specific elicitation, these temporal patterns are significantly altered. The differences in timing, intensity and extent of responses during different modes of disease resistance expression indicate that stimulation of cultured plant cells with non-specific soluble fractions in order to model in planta events during plant / Oomycete and, by implication, plant / fungal interactions, has significant limitations.

Allelopathy, DIMBOA production and genetic variability in accessions of Triticum speltoides

A screening was conducted to study the allelopathic potential of Australian-held accessions of Triticum speltoides. Of 26 accessions, four were found to inhibit root growth in the indicator species, lettuce (Lactuca sativa). The methanol leaf extracts of these accessions significantly reduced the root length of wild oat (Avena spp.). In all but one case, alellopathic accessions contained higher amounts of DIMBOA than did nonallelopathic accessions. Since some variation in allelopathic response was detected within lines, random amplified polymorphic DNA (RAPD) markers were used to estimate genetic diversity between and within the allelopathic accessions of Triticum speltoides L. The average genetic similarity between all possible pairs of selected accessions was found to be 55% and ranged from 44% to 88%. Comparison of DNA extracted from different single seedlings within the same accession revealed significant intraaccession genetic diversity (4-24%), although this was much less than that observed between accessions tested. This intraaccession diversity has significant implications for the selection of T. speltoides accessions in breeding or screening programs.

Hydrogen peroxide yields during the incompatible interaction of tobacco suspension cells inoculated with Phytophthora nicotianae

Rates of H(2)O(2) production by tobacco suspension cells inoculated with zoospores from compatible or incompatible races of the pathogen Phytophthora nicotianae were followed by direct measurement of oxygen evolution from culture supernatants following catalase addition. Rates of HO(2)(*)/O(2)(-) production were compared by following the formation of the formazan of sodium, 3'-[1-[phenylamino-carbonyl]-3,4-tetrazolium]-bis(4-methoxy-6-nitro) benzene-sulfonic acid hydrate. In the incompatible interaction only, both reactive oxygen species (ROS) were produced by the cultured host cells in a minor burst between 0 and 2 h and then in a major burst between 8 and 12 h after inoculation. Absolute levels of H(2)O(2) could not be accurately measured due to its metabolism by host cells, but results are consistent with the majority of H(2)O(2) being formed via dismutation of HO(2)(*)/O(2)(-). The effects of inhibitors of endogenous Cu/Zn superoxide dismutase (diethyldithiocarbamate) and catalase (3-amino-1,2,4-triazole and salicylic acid) were also examined. Yields of ROS in the presence of the inhibitors diphenylene iodonium, allopurinol, and salicylhydroxamic acid suggest that ROS were generated in incompatible host responses by more than one mechanism.

Use of a new tetrazolium-based assay to study the production of superoxide radicals by tobacco cell cultures challenged with avirulent zoospores of phytophthora parasitica var nicotianae

The relationship between the production of reactive oxygen species and the hypersensitive response (HR) of tobacco (Nicotiana tabacum L. ) toward an incompatible race of the Oomycete Phytophthora parasitica var nicotianae has been investigated. A new assay for superoxide radical (O2-) production based on reduction of the tetrazolium dye sodium,3'-(1-[phenylamino-carbonyl]-3, 4-tetrazolium)-bis(4-methoxy-6-nitro) benzene-sulfonic acid hydrate (XTT) has enabled the quantitative estimation of perhydroxyl/superoxide radical acid-base pair (HO2./O2-) production during the resistant response. Tobacco suspension cells were inoculated with zoospores from compatible or incompatible races of the pathogen. Subsequent HO2./O2- production was monitored by following the formation of XTT formazan. In the incompatible interaction only, HO2./O2- was produced in a minor burst between 0 and 2 h and then in a major burst between 8 and 10 h postinoculation. During this second burst, rates of XTT reduction equivalent to a radical flux of 9.9 x 10(-15) mol min-1 cell-1 were observed. The HO2./O2- scavengers O2- dismutase and Mn(III)desferal each inhibited dye reduction. An HR was observed in challenged, resistant cells immediately following the second burst of radical production. Both scavengers inhibited the HR when added prior to the occurrence of either radical burst, indicating that O2- production is a necessary precursor to the HR.

Segregation of glutenins in wheat × maize-derived doubled haploid wheat populations

The segregation of both high and low molecular weight glutenin subunits across 7 F1 wheat (Triticum aestivum L.) × maize (Zea mays L.) derived doubled haploid populations was examined. The F1 wheats used in each population were produced from parents of interest to Australian wheat breeding programs. The parents varied by up to 5 glutenin subunit loci. Examination of subunits individually within each population using a chi-square analysis revealed that all but 2 of the 26 pairs of alleles analysed fitted the expected 1 : 1 segregation ratio. Glutenin profiles were examined for each cross individually and all but one (Sonalika/Hartog) fitted the expected Mendelian segregation pattern. The analysis of allele distribution of the 6 glutenin loci across all 7 crosses showed all falling well within expected segregation ratios. Closer examination of parental lines and populations revealed irregularities which conflict with original assumptions and provide a valid explanation for the few segregation distortions observed. It is concluded that wheat × maize-derived doubled haploid populations represent a unbiased assortment of parental gametes on both arms of Group 1 chromosomes.

The tetrazolium dyes MTS and XTT provide new quantitative assays for superoxide and superoxide dismutase

The tetrazolium dyes MTS and XTT were reduced to their soluble formazans by superoxide radical anions (O2-) produced by the oxidation of xanthine by xanthine oxidase under standard conditions. These reactions were compared to the well-known reductions of NBT and cytochrome c by the xanthine/xanthine oxidase system. Reduction of the dyes was completely inhibited by superoxide dismutase (SOD). Rate constants for the reaction of MTS and XTT with O2- were estimated at 1.3 +/- .1 x 10(5) M-1S-1 and 8.6 x 10(4) M-1S-1 respectively. The stable MTS and XTT formazans have high extinction coefficients in the visible range which enable sensitive detection and quantification of superoxide radicals, avoiding some of the problems inherent in assays based on production of the insoluble NBT formazan. MTS and XTT have considerable potential both for the quantitative assay of radical production in living tissues and for the assay of superoxide dismutase activity in tissue extracts. Implications for the interpretation of cell culture growth assays which employ these dyes are discussed.

The prevention of violent spinal cord injuries

Interpersonal violence has been defined by the USPHS as a national critical health care problem. Of the 10,000 to 12,000 new spinal cord injuries in the United States each year, about a 1,000 will be caused by gunshot wounds. Violence is identified as part of our heritage, inherent in our entertainment and, sadly, part of our everyday life. Community response to these intentional injuries has indicated they will no longer be ignored. Conventional prevention efforts are often not relevant. Violence prevention efforts require the focus to be upon the critical precipitating factors. The development of school, community and youth-based violence-specific injury prevention programs are essential.

Effects of t-butyl hydroperoxide on NADPH, glutathione, and the respiratory burst of rat alveolar macrophages

The effects of t-butyl hydroperoxide on glutathione and NADPH and the respiratory burst (an NADPH-dependent function) in rat alveolar macrophages was investigated. Alveolar macrophages were exposed for 15 min to t-butyl hydroperoxide in the presence or absence of added glucose. Cells were then assayed for concanavalin A-stimulated O2 production or for NADPH, NADP, reduced glutathione, glutathione disulfide, glutathione released into the medium and glutathione mixed disulfides. Exposure of rat alveolar macrophages to 1 X 10(-5) M t-butyl hydroperoxide causes a loss of concanavalin A-stimulated superoxide production (the respiratory burst) that can be prevented or reversed by added glucose. Cells incubated without glucose had a higher oxidation state of the NADPH/NADP couple than cells incubated with glucose. With t-butyl hydroperoxide, NADP rose to almost 100% of the NADP + NADPH pool; however, addition of glucose prevented this alteration of the NADPH oxidation state. Cells exposed to 1 X 10(-5) M t-butyl hydroperoxide in the absence of glucose showed a significant increase in the percentage GSSG in the GSH + GSSG pool and increased glutathione mixed disulfides. These changes in glutathione distribution could also be prevented or reversed by glucose. With 1 X 10(-4) M t-butyl hydroperoxide, changes in glutathione oxidation were not prevented by glucose and cells were irreversibly damaged. We conclude that drastic alteration of the NADPH/NADP ratio does not itself reflect toxicity and that significant alteration of glutathione distribution can also be tolerated; however, when oxidative stress exceeds the ability of glucose to prevent alterations in oxidation state, irreversible damage to cell function and structure may occur.

Selenium deficiency potentiates paraquat-induced lipid peroxidation in isolated perfused rat lung

Glutathione peroxidase (GSHPx), a seleno-enzyme, reduces lipid hydroperoxides while producing oxidized glutathione (GSSG), which can efflux from cells. To study the role of GSHPx in antioxidant defense, isolated lungs from selenium-deficient rats were perfused for 2 h with or without 1 mM paraquat. Perfusate GSSG was measured as an index of GSHPx activity, and malondialdehyde (MDA) as an index of lipid peroxidation. Selenium deficiency decreased lung GSHPx activity 75-80%. During perfusion control lungs showed GSSG efflux of 8.5 +/- 4.5 nmol/h and with paraquat 49.1 +/- 12.1 nmol/h. Selenium-deficient lungs with or without paraquat showed GSSG efflux of 16.4 +/- 5.3 and 13.7 +/- 8.9 nmol/h, respectively. MDA efflux occurred only in paraquat-perfused selenium-deficient lungs (7.8 +/- 2.7 nmol/h). Lung homogenates from this group had lower GSH + GSSG than the other three groups. These results indicate an inverse correlation between GSSG efflux and MDA accumulation from paraquat-perfused lungs and suggest that increased turnover of the GSHPx reaction protects paraquat-perfused lungs from lipid peroxidation.

Oxygen toxicity: loss of lung macrophage function without metabolite depletion

Hyperoxia inhibited concanavalin A stimulated O2- release (respiratory burst) of alveolar macrophages obtained by bronchoalveolar lavage from rats. After 36 h of normobaric 100% O2, a partial reversal (48%) of the inhibition was produced by addition of glucose. Since oxidant-induced, reversible NADPH depletion correlates with reversible inhibition of the respiratory burst, intracellular NADPH was assayed to determine whether irreversible inhibition of the respiratory burst was related to persistent changes in this metabolite. The cellular concentrations of ATP, glutathione, and ascorbate were also measured. After 36 h of hyperoxia, NADPH concentration in alveolar macrophages rose slightly while ATP and glutathione content remained at control levels. Ascorbate levels fell significantly but were not responsible for respiratory burst inhibition. Thus, irreversible loss of cellular function in hyperoxia is not due to persistent alterations in these metabolites. Significant amounts of both glutathione and ascorbate were found in extracellular fractions of lung washings, indicating high concentrations in the aqueous subphase in the lung fluid lining. There was no change in total content of these extracellular antioxidants following O2 exposure.

Studies of the reactivity of HO2/O2- with unsaturated hydroperoxides in ethanolic solutions

A study of the reactivity of HO2/O2- with unsaturated hydroperoxides/peroxides was carried out in a stopped-flow spectrophotometer equipped with an O2--generating plasma lamp. The results show that, in 80% aqueous ethanol solution containing either 0.05 M H2SO4 (for HO2 studies) or 0.005 M KOH (for O2- studies), these oxy-radicals do not react with oleic acid hydroperoxide, linoleic acid hydroperoxide, 1-hydroperoxy-2-cyclooctene, and tert-butyl allyl peroxide. These findings are discussed in the light of conflicting evidence concerning the reaction of HO2/O2- with organic hydroperoxides/peroxides.

A study of the reactivity of HO2/O2- with unsaturated fatty acids

The reaction of perhydroxyl radical (HO2) with linoleic, linolenic, and arachidonic acids has been studied in aqueous ethanolic solutions by the stopped flow technique. The corresponding rate constants are 1.2 x 10(3), 1.7 x 10(3), and 3.0 x 10(3) M-1 S-1, respectively. While kinetic results suggest that the HO2 radical reacts with the double allylic H atom of the polyunsaturated fatty acids, thermodynamic approximations indicate that the reaction is exothermic by approximately 10 kcal/mol. The relevance of this reaction to membrane damage observed in biological systems that have been exposed to HO2/O2- radicals is discussed.

Purification of oleic acid and linoleic acid

To permit kinetic studies of the reactivity of unsaturated fatty acids towards oxygen radicals, it is essential to remove traces of hydroperoxides and other conjugated lipid impurities commonly present in commercial samples. Removal of these impurities has been satisfactorily achieved for oleic and linoleic acids by anaerobic low temperature recrystallization from acetonitrile. The UV spectra of commercial and purified samples are compared.