Dynamic Reconfiguration of Switchgrass Proteomes in Response to Rust (Puccinia novopanici) Infection

Switchgrass (Panicum virgatum L.) can be infected by the rust pathogen (Puccinia novopanici) and results in lowering biomass yields and quality. Label-free quantitative proteomics was conducted on leaf extracts harvested from non-infected and infected plants from a susceptible cultivar (Summer) at 7, 11, and 18 days after inoculation (DAI) to follow the progression of disease and evaluate any plant compensatory mechanisms to infection. Some pustules were evident at 7 DAI, and their numbers increased with time. However, fungal DNA loads did not appreciably change over the course of this experiment in the infected plants. In total, 3830 proteins were identified at 1% false discovery rate, with 3632 mapped to the switchgrass proteome and 198 proteins mapped to different Puccinia proteomes. Across all comparisons, 1825 differentially accumulated switchgrass proteins were identified and subjected to a STRING analysis using Arabidopsis (A. thaliana L.) orthologs to deduce switchgrass cellular pathways impacted by rust infection. Proteins associated with plastid functions and primary metabolism were diminished in infected Summer plants at all harvest dates, whereas proteins associated with immunity, chaperone functions, and phenylpropanoid biosynthesis were significantly enriched. At 18 DAI, 1105 and 151 proteins were significantly enriched or diminished, respectively. Many of the enriched proteins were associated with mitigation of cellular stress and defense.

Divergent Metabolic Changes in Rhizomes of Lowland and Upland Switchgrass (Panicum virgatum) from Early Season through Dormancy Onset

High-biomass-yielding southerly adapted switchgrasses (Panicum virgatum L.) frequently suffer from unpredictable winter hardiness at more northerly sites arising from damage to rhizomes that prevent effective spring regrowth. Previously, changes occurring over the growing season in rhizomes sampled from a cold-adapted tetraploid upland cultivar, Summer, demonstrated a role for abscisic acid (ABA), starch accumulation, and transcriptional reprogramming as drivers of dormancy onset and potential keys to rhizome health during winter dormancy. Here, rhizome metabolism of a high-yielding southerly adapted tetraploid switchgrass cultivar, Kanlow-which is a significant source of genetics for yield improvement-was studied over a growing season at a northern site. Metabolite levels and transcript abundances were combined to develop physiological profiles accompanying greening through the onset of dormancy in Kanlow rhizomes. Next, comparisons of the data to rhizome metabolism occurring in the adapted upland cultivar Summer were performed. These data revealed both similarities as well as numerous differences in rhizome metabolism that were indicative of physiological adaptations unique to each cultivar. Similarities included elevated ABA levels and accumulation of starch in rhizomes during dormancy onset. Notable differences were observed in the accumulation of specific metabolites, the expression of genes encoding transcription factors, and several enzymes linked to primary metabolism.

The genetic basis for panicle trait variation in switchgrass (Panicum virgatum)

We investigate the genetic basis of panicle architecture in switchgrass in two mapping populations across a latitudinal gradient, and find many stable, repeatable genetic effects and limited genetic interactions with the environment. Grass species exhibit large diversity in panicle architecture influenced by genes, the environment, and their interaction. The genetic study of panicle architecture in perennial grasses is limited. In this study, we evaluate the genetic basis of panicle architecture including panicle length, primary branching number, and secondary branching number in an outcrossed switchgrass QTL population grown across ten field sites in the central USA through multi-environment mixed QTL analysis. We also evaluate genetic effects in a diversity panel of switchgrass grown at three of the ten field sites using genome-wide association (GWAS) and multivariate adaptive shrinkage. Furthermore, we search for candidate genes underlying panicle traits in both of these independent mapping populations. Overall, 18 QTL were detected in the QTL mapping population for the three panicle traits, and 146 unlinked genomic regions in the diversity panel affected one or more panicle trait. Twelve of the QTL exhibited consistent effects (i.e., no QTL by environment interactions or no QTL × E), and most (four of six) of the effects with QTL × E exhibited site-specific effects. Most (59.3%) significant partially linked diversity panel SNPs had significant effects in all panicle traits and all field sites and showed pervasive pleiotropy and limited environment interactions. Panicle QTL co-localized with significant SNPs found using GWAS, providing additional power to distinguish between true and false associations in the diversity panel.

Effect of cultivar and temperature on the synergistic interaction between panicum mosaic virus and satellite panicum mosaic virus in switchgrass

Panicum mosaic virus (PMV), the type member of the genus Panicovirus in the family Tombusviridae, naturally infects switchgrass (Panicum virgatum L.). PMV and its molecular partner, satellite panicum mosaic virus (SPMV), interact synergistically in coinfected millets to exacerbate the disease phenotype and increase the accumulation of PMV compared to plants infected with PMV alone. In this study, we examined the reaction of switchgrass cvs. Summer and Kanlow to PMV and PMV+SPMV infections at 24°C and 32°C. Switchgrass cv. Summer was susceptible to PMV at both temperatures. In contrast, cv. Kanlow was tolerant to PMV at 24°C, but not at 32°C, suggesting that Kanlow harbors temperature-sensitive resistance to PMV. At 24°C, PMV was readily detected in inoculated leaves, but not in upper uninoculated leaves of Kanlow, suggesting that resistance to PMV was likely mediated by abrogation of long-distance virus transport. Coinfection by PMV and SPMV at 24°C and 32°C in cv. Summer, but not in Kanlow, caused increased symptomatic systemic infection and mild disease synergism with slightly increased PMV accumulation compared to plants infected with PMV alone. These data suggest that the interaction between PMV and SPMV in switchgrass is cultivar-dependent, manifested in Summer but not in Kanlow. However, co-inoculation of cv. Kanlow with PMV+SPMV caused an enhanced asymptomatic infection, suggesting a role of SPMV in enhancement of symptomless infection in a tolerant cultivar. These data suggest that enhanced asymptomatic infections in a virus-tolerant switchgrass cultivar could serve as a source of virus spread and play an important role in panicum mosaic disease epidemiology under field conditions. Our data reveal that the cultivar, coinfection with SPMV, and temperature influence the severity of symptoms elicited by PMV in switchgrass.

Geographic variation in the genetic basis of resistance to leaf rust between locally adapted ecotypes of the biofuel crop switchgrass (Panicum virgatum)

Local adaptation is an important process in plant evolution, which can be impacted by differential pathogen pressures along environmental gradients. However, the degree to which pathogen resistance loci vary in effect across space and time is incompletely described. To understand how the genetic architecture of resistance varies across time and geographic space, we quantified rust (Puccinia spp.) severity in switchgrass (Panicum virgatum) plantings at eight locations across the central USA for 3 yr and conducted quantitative trait locus (QTL) mapping for rust progression. We mapped several variable QTLs, but two large-effect QTLs which we have named Prr1 and Prr2 were consistently associated with rust severity in multiple sites and years, particularly in northern sites. By contrast, there were numerous small-effect QTLs at southern sites, indicating a genotype-by-environment interaction in rust resistance loci. Interestingly, Prr1 and Prr2 had a strong epistatic interaction, which also varied in the strength and direction of effect across space. Our results suggest that abiotic factors covarying with latitude interact with the genetic loci underlying plant resistance to control rust infection severity. Furthermore, our results indicate that segregating genetic variation in epistatically interacting loci may play a key role in determining response to infection across geographic space.

Management controls the net greenhouse gas outcomes of growing bioenergy feedstocks on marginally productive croplands

Bio-based energy is key to developing a globally sustainable low-carbon economy. Lignocellulosic feedstock production on marginally productive croplands is expected to provide substantial climate mitigation benefits, but long-term field research comparing greenhouse gas (GHG) outcomes during the production of annual versus perennial crop-based feedstocks is lacking. Here, we show that long-term (16 years) switchgrass (Panicum virgatum L.) systems mitigate GHG emissions during the feedstock production phase compared to GHG-neutral continuous corn (Zea mays L.) under conservation management on marginally productive cropland. Increased soil organic carbon was the major GHG sink in all feedstock systems, but net agronomic GHG outcomes hinged on soil nitrous oxide emissions controlled by nitrogen (N) fertilizer rate. This long-term field study is the first to demonstrate that annual crop and perennial grass systems respectively maintain or mitigate atmospheric GHG contributions during the agronomic phase of bioenergy production, providing flexibility for land-use decisions on marginally productive croplands.

Transcriptome divergence during leaf development in two contrasting switchgrass (Panicum virgatum L.) cultivars

The genetics and responses to biotic stressors of tetraploid switchgrass (Panicum virgatum L.) lowland cultivar 'Kanlow' and upland cultivar Summer are distinct and can be exploited for trait improvement. In general, there is a paucity of data on the basal differences in transcription across tissue developmental times for switchgrass cultivars. Here, the changes in basal and temporal expression of genes related to leaf functions were evaluated for greenhouse grown 'Kanlow', and 'Summer' plants. Three biological replicates of the 4th leaf pooled from 15 plants per replicate were harvested at regular intervals beginning from leaf emergence through senescence. Increases and decreases in leaf chlorophyll and N content were similar for both cultivars. Likewise, multidimensional scaling (MDS) analysis indicated both cultivar-independent and cultivar-specific gene expression. Cultivar-independent genes and gene-networks included those associated with leaf function, such as growth/senescence, carbon/nitrogen assimilation, photosynthesis, chlorophyll biosynthesis, and chlorophyll degradation. However, many genes encoding nucleotide-binding leucine rich repeat (NB-LRRs) proteins and wall-bound kinases associated with detecting and responding to environmental signals were differentially expressed. Several of these belonged to unique cultivar-specific gene co-expression networks. Analysis of genomic resequencing data provided several examples of NB-LRRs genes that were not expressed and/or apparently absent in the genomes of Summer plants. It is plausible that cultivar (ecotype)-specific genes and gene-networks could be one of the drivers for the documented differences in responses to leaf-borne pathogens between these two cultivars. Incorporating broad resistance to plant pathogens in elite switchgrass germplasm could improve sustainability of biomass production under low-input conditions.

Dedicated Bioenergy Crops and Water Erosion

Information on the water quality impact of perennial warm-season grasses (WSGs) when grown in marginal lands as dedicated energy crops is limited. We studied how WSGs affected runoff, sediment, and nutrient losses and related near-surface soil properties to those of no-till corn ( L.) on an eroded soil in southwestern Iowa and a center pivot corner in east-central Nebraska. The experiment at the eroded soil was established in 2012, and treatments included 'Liberty' switchgrass ( L.) and no-till continuous corn. The experiment at the pivot corner was established in 2013 with 'Liberty' switchgrass, 'Shawnee' switchgrass, low-diversity grass mixture, and corn. We simulated rainfall at 63.5 ± 2.8 mm h for 1 h to portray 5-yr return periods and measured water erosion in spring 2017. Time to runoff start and runoff depth did not differ between WSGs and corn. On the eroded soil, sediment and nutrient losses did not differ between treatments. At the pivot corner, sediment (0.71 vs. 0.15 Mg ha) and PO-P (0.037 vs. 0.006 kg ha) losses were five times higher in corn than in WSGs. Near-surface soil properties did not differ on the eroded soil, but at the pivot corner, wet aggregate stability was four times higher and residue cover was 34% higher in WSGs than in corn. Water-stable aggregates were negatively correlated with NO-N and PO-P losses. Overall, WSGs can improve water quality in marginally productive croplands, but their effectiveness appears to be site specific.

Isolation and Analysis of Microbial Communities in Soil, Rhizosphere, and Roots in Perennial Grass Experiments

Plant and soil microbiome studies are becoming increasingly important for understanding the roles microorganisms play in agricultural productivity. The purpose of this manuscript is to provide detail on how to rapidly sample soil, rhizosphere, and endosphere of replicated field trials and analyze changes that may occur in the microbial communities due to sample type, treatment, and plant genotype. The experiment used to demonstrate these methods consists of replicated field plots containing two, pure, warm-season grasses (Panicum virgatum and Andropogon gerardii) and a low-diversity grass mixture (A. gerardii, Sorghastrum nutans, and Bouteloua curtipendula). Briefly, plants are excavated, a variety of roots are cut and placed in phosphate buffer, and then shaken to collect the rhizosphere. Roots are brought to the laboratory on ice and surface sterilized with bleach and ethanol (EtOH). The rhizosphere is filtered and concentrated by centrifugation. Excavated soil from around the root ball is placed into plastic bags and brought to the lab where a small amount of soil is taken for DNA extractions. DNA is extracted from roots, soil, and rhizosphere and then amplified with primers for the V4 region of the 16S rRNA gene. Amplicons are sequenced, then analyzed with open access bioinformatics tools. These methods allow researchers to test how the microbial community diversity and composition varies due to sample type, treatment, and plant genotype. Using these methods along with statistical models, the representative results demonstrate there are significant differences in microbial communities of roots, rhizosphere, and soil. Methods presented here provide a complete set of steps for how to collect field samples, isolate, extract, quantify, amplify, and sequence DNA, and analyze microbial community diversity and composition in replicated field trials.

Seasonal below-ground metabolism in switchgrass

Switchgrass (Panicum virgatum), a perennial, polyploid, C4 warm-season grass is among the foremost herbaceous species being advanced as a source of biomass for biofuel end uses. At the end of every growing season, the aerial tissues senesce, and the below-ground rhizomes become dormant. Future growth is dependent on the successful over-wintering of the rhizomes. Although the importance of rhizome health to overall year-upon-year plant productivity has been long recognized, there is limited information on seasonal changes occurring during dormancy at both the transcriptome and metabolite levels. Here, global changes in transcriptomes and metabolites were investigated over two growing seasons in rhizomes harvested from field-grown plants. The objectives were: (a) synthesize information on cellular processes that lead to dormancy; and (b) provide models that could account for major metabolic pathways present in dormant switchgrass rhizomes. Overall, metabolism during dormancy appeared to involve discrete but interrelated events. One was a response to abscisic acid that resulted in dehydration, increases in osmolytes and upregulation of autophagic processes, likely through the target of rapamycin complex and sucrose non-fermentative-related kinase-based signaling cascades. Another was a recalibration of energy transduction through apparent reductions in mitochondrial oxidative phosphorylation, increases in substrate level generation of ATP and reducing equivalents, and recycling of N and possibly CO₂ through refixation. Lastly, transcript abundances indicated that cold-related signaling was also occurring. Altogether, these data provide a detailed overview of rhizome metabolism, especially during dormancy, which can be exploited in the future to improve winter survival in switchgrass.

Energy potential and greenhouse gas emissions from bioenergy cropping systems on marginally productive cropland

Low-carbon biofuel sources are being developed and evaluated in the United States and Europe to partially offset petroleum transport fuels. Current and potential biofuel production systems were evaluated from a long-term continuous no-tillage corn (Zea mays L.) and switchgrass (Panicum virgatum L.) field trial under differing harvest strategies and nitrogen (N) fertilizer intensities to determine overall environmental sustainability. Corn and switchgrass grown for bioenergy resulted in near-term net greenhouse gas (GHG) reductions of -29 to -396 grams of CO2 equivalent emissions per megajoule of ethanol per year as a result of direct soil carbon sequestration and from the adoption of integrated biofuel conversion pathways. Management practices in switchgrass and corn resulted in large variation in petroleum offset potential. Switchgrass, using best management practices produced 3919±117 liters of ethanol per hectare and had 74±2.2 gigajoules of petroleum offsets per hectare which was similar to intensified corn systems (grain and 50% residue harvest under optimal N rates). Co-locating and integrating cellulosic biorefineries with existing dry mill corn grain ethanol facilities improved net energy yields (GJ ha-1) of corn grain ethanol by >70%. A multi-feedstock, landscape approach coupled with an integrated biorefinery would be a viable option to meet growing renewable transportation fuel demands while improving the energy efficiency of first generation biofuels.

Senescence, dormancy and tillering in perennial C4 grasses

Perennial, temperate, C4 grasses, such as switchgrass and miscanthus have been tabbed as sources of herbaceous biomass for the production of green fuels and chemicals based on a number of positive agronomic traits. Although there is important literature on the management of these species for biomass production on marginal lands, numerous aspects of their biology are as yet unexplored at the molecular level. Perenniality, a key agronomic trait, is a function of plant dormancy and winter survival of the below-ground parts of the plants. These include the crowns, rhizomes and meristems that will produce tillers. Maintaining meristem viability is critical for the continued survival of the plants. Plant tillers emerge from the dormant crown and rhizome meristems at the start of the growing period in the spring, progress through a phase of vegetative growth, followed by flowering and eventually undergo senescence. There is nutrient mobilization from the aerial portions of the plant to the crowns and rhizomes during tiller senescence. Signals arising from the shoots and from the environment can be expected to be integrated as the plants enter into dormancy. Plant senescence and dormancy have been well studied in several dicot species and offer a potential framework to understand these processes in temperate C4 perennial grasses. The availability of latitudinally adapted populations for switchgrass presents an opportunity to dissect molecular mechanisms that can impact senescence, dormancy and winter survival. Given the large increase in genomic and other resources for switchgrass, it is anticipated that projected molecular studies with switchgrass will have a broader impact on related species.

Conversion of switchgrass to ethanol using dilute ammonium hydroxide pretreatment: influence of ecotype and harvest maturity

Switchgrass (Panicum virgatum L.) is a perennial C4 grass that is being developed as a bioenergy crop because it has high production yields and suitable agronomic traits. Five switchgrass biomass samples from upland and lowland switchgrass ecotypes harvested at different stages or maturity were used in this study. Switchgrass samples contained 317.0-385.0 g glucans/kg switchgrass dry basis (db) and 579.3-660.2 g total structural carbohydrates/kg switchgrass, db. Carbohydrate contents were greater for the upland ecotype versus lowland ecotype and increased with harvest maturity. Pretreatment of switchgrass with dilute ammonium hydroxide (8% w/w ammonium loading) at 170 degrees C for 20 min was determined to be effective for preparing switchgrass for enzymatic conversion to monosaccharides; glucose recoveries were 66.9-90.5% and xylose recoveries 60.1-84.2% of maximum and decreased with increased maturity at harvest. Subsequently, pretreated switchgrass samples were converted to ethanol by simultaneous saccharification and fermentation using engineered xylose-fermenting Saccharomyces cerevisiae strain YRH400. Ethanol yields were 176.2-202.01/Mg of switchgrass (db) and followed a similar trend as observed for enzymatic sugar yields.

Ethanol yields and cell wall properties in divergently bred switchgrass genotypes

Genetic modification of herbaceous plant cell walls to increase biofuels yields is a primary bioenergy research goal. Using two switchgrass populations developed by divergent breeding for ruminant digestibility, the contributions of several wall-related factors to ethanol yields was evaluated. Field grown low lignin plants significantly out yielded high lignin plants for conversion to ethanol by 39.1% and extraction of xylans by 12%. However, across all plants analyzed, greater than 50% of the variation in ethanol yields was attributable to changes in tissue and cell wall architecture, and responses of stem biomass to dilute-acid pretreatment. Although lignin levels were lower in the most efficiently converted genotypes, no apparent correlation were seen in the lignin monomer G/S ratios. Plants with higher ethanol yields were associated with an apparent decrease in the lignification of the cortical sclerenchyma, and a marked decrease in the granularity of the cell walls following dilute-acid pretreatment.

Switchgrass

Switchgrass (Panicum virgatum L.) is a warm-season grass that is native to the prairies of North America that is being developed into a biomass energy crop. It has been used in the Great Plains and Midwest USA as a forage and pasture grass for over 50 years and since the early 1990s research has been conducted on it for bioenergy because of several principal attributes. Switchgrass can be grown on marginal land that is not suitable for intensive cultivation on which it can produce high biomass yields with good management. It is a long lived perennial that has low establishment and production costs and it can harvested and handled with conventional forage equipment. There is substantial potential for genetic improvement of switchgrass for biomass energy production by increasing biomass yield and altering cell wall composition to increase liquid energy yields in biorefineries.

Isolation, characterization, and quantification of steroidal saponins in switchgrass (Panicum virgatum L.)

Switchgrass (Panicum virgatum L.) has been identified for development into an efficient and environmentally friendly biomass energy crop. A recent 5 year study demonstrated that switchgrass grown for biofuel production produced 540% more energy than what is needed to grow, harvest, and process it into cellulosic ethanol. If switchgrass is grown on a scale useful for a bioenergy source, some of the material could be used by livestock as hay or pasture. Switchgrass has been reported to cause hepatogenous photosensitization in lambs (Ovis aries) and horses (Equus caballus). In this study, a simple extraction and rapid reversed phase high-performance liquid chromatography-electrospray ionization-mass spectrometry method was developed for quantifying the major saponins in switchgrass samples. Differences in the relative concentrations of different saponins were observed between switchgrass cultivars and plant parts.

Cell-wall composition and accessibility to hydrolytic enzymes is differentially altered in divergently bred switchgrass (Panicum virgatum L.) genotypes

The aims of this study were to understand the genotypic variability in cell-wall composition and cell-wall accessibility to enzymes in select switchgrass plants obtained from two different populations derived from a base population of octaploid cultivars. Population C+3 was developed by three breeding generations for high digestibility and population C-1 developed by one generation of breeding for low digestibility. Above-ground biomass from 12 selected genotypes, three each with high or low digestibility within each population, was analyzed for their cell-wall aromatics and polysaccharides. The ratio of p-coumaric acid/ferulic acid was greater (P < or = 0.05) for the high-lignin C-1 population over the low-lignin C+3 population, although the amounts of these two phenolics did not differ between populations. Combined values of guaiacyl + syringyl-lignin were consistently higher in genotypes from the C-1 population as compared to the genotypes from the C+3 population. Overall, p-coumaric acid was released by enzymes in greater amounts than ferulic acid in all these genotypes. Genotypes in the C-1 population exhibited lower dry weight loss as compared to the genotypes in the C+3 population after enzymatic digestion, suggesting changes in cell-wall architecture. Overall, our data highlight the phenotypic plasticity coded by the switchgrass genome and suggest that combining dry matter digestibility with other more specific cell-wall traits could result in genotypes with greater utility as bioenergy feedstocks.

ABA, ROS and NO are Key Players During Switchgrass Seed Germination

Seed dormancy and germination are complex physiological processes usually under hormonal control. Germination of seeds from many plants including switchgrass, are inhibited by ABA and promoted by NO or ROS. However, ABA apparently requires both ROS and NO as intermediates in its action, with ROS produced by membrane-bound NADPH-oxidases responsive to ABA. In switchgrass seeds, externally supplied hydrogen peroxide (ROS), but not NO will overcome ABA-imposed inhibition of germination. Stimulation of germination by external ROS can be partially blocked by NO-scavengers, suggesting that NO is required for seed germination in switchgrass as well as for ABA-induced inhibition of germination. Collectively, these data suggest that multiple mechanisms might be required to sense and respond to varying levels of ABA, NO and ROS in switchgrass seeds.

Reactive oxygen species, ABA and nitric oxide interactions on the germination of warm-season C4-grasses

Hydrogen peroxide (H(2)O(2)) as a source of reactive oxygen species (ROS) significantly stimulated germination of switchgrass (Panicum virgatum L.) seeds with an optimal concentration of 20 mM at both 25 and 35 degrees C. For non-dormant switchgrass seeds exhibiting different levels of germination, treatment with H(2)O(2) resulted in rapid germination (<3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H(2)O(2) elicited simultaneous growth of the root and shoot system, resulting in more uniform seedling development. Seeds of big bluestem (Andropogon gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash] also responded positively to H(2)O(2) treatment, indicating the universality of the effect of H(2)O(2) on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor, diphenyleneiodonium (DPI) at 20 microM retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase activity in seeds. H(2)O(2) reversed the inhibitory effects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition of root elongation. Treatment with H(2)O(2) appeared to enhance endogenous production of nitric oxide, and a scavenger of nitric oxide abolished the peroxide-responsive stimulation of switchgrass seed germination. The activities and levels of several proteins changed earlier in seeds imbibed on H(2)O(2) as compared to seeds maintained on water or on ABA. These data demonstrate that seed germination of warm-season grasses is significantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS and NO in this system.

A Method for Knowledge Modeling

Since knowledge management (KM) is considered to be an important function of a successful business operation, many organizations are embracing KM. The success of a KM project is dependent upon its contents. This article presents a method for building an effective knowledge model that can help businesses to analyze and specify knowledge content. The method takes a decision-oriented view. For the modeling language of the method, Unified Modeling Language (UML) has been chosen. The method is applied to the vessel scheduling process in a maritime shipping company. The steps and rules are explained using an example, and the strengths and weaknesses of the method are discussed.

Nitric oxide accelerates seed germination in warm-season grasses

The nitric oxide (NO) donor sodium nitroprusside (SNP) significantly promoted germination of switchgrass (Panicum virgatum L. cv Kanlow) in the light and in the dark at 25 degrees C, across a broad range of concentrations. SNP also promoted seed germination in two other warm-season grasses. A chemical scavenger of NO inhibited germination and blocked SNP stimulation of seed germination. The phenolic (+)-catechin acted synergistically with SNP and nitrite in promoting seed germination. Acidified nitrite, an alternate NO donor also significantly stimulated seed germination. Interestingly, sodium cyanide, potassium ferricyanide and potassium ferrocyanide at 200 microM strongly enhanced seed germination as well, whereas potassium chloride was without effect. Ferrocyanide and cyanide stimulation of seed germination was blocked by an NO scavenger. Incubation of seeds with a fluorescent NO-specific probe provided evidence for NO production in germinating switchgrass seeds. Abscisic acid (ABA) at 10 microM depressed germination, inhibited root elongation and essentially abolished coleoptile emergence. SNP partially overcame ABA effects on radicle emergence but did not overcome the effects of ABA on coleoptile elongation. Light microscopy indicated extension of the radicle and coleoptiles in seeds maintained on water or on SNP after 2 days. In contrast, there was minimal growth of the radicle and coleoptile in ABA-treated seeds even after 3-4 days. These data indicate that seed germination of warm-season grasses is significantly influenced by NO signaling pathways and document that NO could be an endogenous trigger for release from dormancy in these species.

Nitric oxide accelerates seed germination in warm-season grasses

The nitric oxide (NO) donor sodium nitroprusside (SNP) significantly promoted germination of switchgrass (Panicum virgatum L. cv Kanlow) in the light and in the dark at 25 degrees C, across a broad range of concentrations. SNP also promoted seed germination in two other warm-season grasses. A chemical scavenger of NO inhibited germination and blocked SNP stimulation of seed germination. The phenolic (+)-catechin acted synergistically with SNP and nitrite in promoting seed germination. Acidified nitrite, an alternate NO donor also significantly stimulated seed germination. Interestingly, sodium cyanide, potassium ferricyanide and potassium ferrocyanide at 200 microM strongly enhanced seed germination as well, whereas potassium chloride was without effect. Ferrocyanide and cyanide stimulation of seed germination was blocked by an NO scavenger. Incubation of seeds with a fluorescent NO-specific probe provided evidence for NO production in germinating switchgrass seeds. Abscisic acid (ABA) at 10 microM depressed germination, inhibited root elongation and essentially abolished coleoptile emergence. SNP partially overcame ABA effects on radicle emergence but did not overcome the effects of ABA on coleoptile elongation. Light microscopy indicated extension of the radicle and coleoptiles in seeds maintained on water or on SNP after 2 days. In contrast, there was minimal growth of the radicle and coleoptile in ABA-treated seeds even after 3-4 days. These data indicate that seed germination of warm-season grasses is significantly influenced by NO signaling pathways and document that NO could be an endogenous trigger for release from dormancy in these species.

Fire and grazing effects on wind erosion, soil water content, and soil temperature

Selective grazing of burned patches can be intense if animal distribution is not controlled and may compound the independent effects of fire and grazing on soil characteristics. Our objectives were to quantify the effects of patch burning and grazing on wind erosion, soil water content, and soil temperature in sand sagebrush (Artemisia filifolia Torr.) mixed prairie. We selected 24, 4-ha plots near Woodward, OK. Four plots were burned during autumn (mid-November) and four during spring (mid-April), and four served as nonburned controls for each of two years. Cattle were given unrestricted access (April-September) to burned patches (<2% of pastures) and utilization was about 78%. Wind erosion, soil water content, and soil temperature were measured monthly. Wind erosion varied by burn, year, and sampling height. Wind erosion was about 2 to 48 times greater on autumn-burned plots than nonburned plots during the dormant period (December-April). Growing-season (April-August) erosion was greatest during spring. Erosion of spring-burned sites was double that of nonburned sites both years. Growing-season erosion from autumn-burned sites was similar to nonburned sites except for one year with a dry April-May. Soil water content was unaffected by patch burn treatments. Soils of burned plots were 1 to 3 degrees C warmer than those of nonburned plots, based on mid-day measurements. Lower water holding and deep percolation capacity of sandy soils probably moderated effects on soil water content and soil temperature. Despite poor growing conditions following fire and heavy selective grazing of burned patches, no blowouts or drifts were observed.

Pott's puffy tumour: a rare cause of forehead swelling in a child

We report a case of Pott's puffy tumour in a 12-year-old. Owing to the late development of the frontal sinuses, frontal sinus infection in children is rare. When present it can lead to osteomyelitis associated with forehead swelling. Early diagnosis and active treatment prevent progression to life-threatening intracranial spread.

Management and outcome of choanal atresia correction

OBJECTIVES

Outcome analyses of factors that may either maximize success or predict a better outcome following choanal atresia correction.

METHODS

A retrospective review of children undergoing choanal atresia correction at Great Ormond Street Hospital for Children, London between January 1990 and April 1998. Children with unilateral or bilateral choanal atresia were studied. In all cases, correction was by a transnasal approach under endoscopic control. A 120 degrees Hopkins rod telescope was used to visualize the atretic plate from the nasopharynx. Straight urethral sounds were used to perforate the plate followed by use of an air drill to remove the bony component. Portex endotracheal tubes were subsequently inserted as nasal stents.

RESULTS

Sixty-five children (19 M, 46 F: age range 1 day to 17 years) presented with choanal atresia and the outcomes for 46 were included in the study. Twenty-six patients (40%) had other major anomalies. In children with unilateral atresia neither duration of stenting nor presence of facial anomalies had an impact on outcome. Of those children with bilateral choanal atresia and associated facial anomalies (n=9), 56% were asymptomatic following correction. In children with isolated bilateral choanal atresia (n=19), 74% were asymptomatic following correction; 29% (n2.3 kg (n3. 5 mm (n=6) had an 83% chance of a good outcome. Those patients stented with a tube </=3.5 mm (n=22) had only a 64% success rate. None of the patients who were stented for at least 12 weeks remained symptomatic.

CONCLUSIONS

Neonates with bilateral choanal atresia who were stented for at least 12 weeks with the largest Portex tube that comfortably passed through the anterior nares had the best outcome. If they had either associated anomalies or low weight at surgery, they were less likely to become asymptomatic. For patients with unilateral choanal atresia, neither the presence of facial anomalies nor stent duration had an impact on outcome.

Langerhans' cell histiocytosis--a rare cause of sudden onset unilateral sensorineural hearing loss

Langerhans' cell histiocytosis is a rare disorder of unknown aetiology in which pathological Langerhans' cells accumulate and destroy local tissue. We report a 38-year-old female who presented with a sudden onset of left sensorineural hearing loss. Magnetic resonance imaging (MRI) revealed a contrast-enhancing lesion in the left mastoid and a second lesion in the hypothalamus. Following left mastoid exploration and biopsy a definitive diagnosis of Langerhans' cell histiocytosis was made and the patient was treated with external beam radiotherapy. Subsequent right femur and right mastoid involvement were successfully treated with steroids and cytotoxic chemotherapy. At one year follow-up the patient had residual left-sided sensorineural hearing loss with normal hearing in the right ear. To our knowledge, Langerhans' cell histiocytosis has not been previously reported as a cause of unilateral sudden onset sensorineural hearing loss. It should be considered in the differential diagnosis of this condition.

American Society of Clinical Oncology clinical practice guidelines for the use of chemotherapy and radiotherapy protectants

PURPOSE

Because toxicities associated with chemotherapy and radiotherapy can adversely affect short- and long-term patient quality of life, can limit the dose and duration of treatment, and may be life-threatening, specific agents designed to ameliorate or eliminate certain chemotherapy and radiotherapy toxicities have been developed. Variability in interpretation of the available data pertaining to the efficacy of the three United States Food and Drug Administration-approved agents that have potential chemotherapy- and radiotherapy-protectant activity-dexrazoxane, mesna, and amifostine-and questions about the role of these protectant agents in cancer care led to concern about the appropriate use of these agents. The American Society of Clinical Oncology sought to establish evidence-based, clinical practice guidelines for the use of dexrazoxane, mesna, and amifostine in patients who are not enrolled on clinical treatment trials.

METHODS

A multidisciplinary Expert Panel reviewed the clinical data regarding the activity of dexrazoxane, mesna, and amifostine. A computerized literature search was performed using MEDLINE. In addition to reports collected by individual Panel members, all articles published in the English-speaking literature from June 1997 through December 1998 were collected for review by the Panel chairpersons, and appropriate articles were distributed to the entire Panel for review. Guidelines for use, levels of evidence, and grades of recommendation were reviewed and approved by the Panel. Outcomes considered in evaluating the benefit of a chemotherapy- or radiotherapy-protectant agent included amelioration of short- and long-term chemotherapy- or radiotherapy-related toxicities, risk of tumor protection by the agent, toxicity of the protectant agent itself, quality of life, and economic impact. To the extent that these data were available, the Panel placed the greatest value on lesser toxicity that did not carry a concomitant risk of tumor protection.

RESULTS AND CONCLUSION

Mesna: (1) Mesna, dosed as detailed in these guidelines, is recommended to decrease the incidence of standard-dose ifosfamide-associated urothelial toxicity. (2) There is insufficient evidence on which to base a guideline for the use of mesna to prevent urothelial toxicity with ifosfamide doses that exceed 2.5 g/m(2)/d. (3) Either mesna or forced saline diuresis is recommended to decrease the incidence of urothelial toxicity associated with high-dose cyclophosphamide use in the stem-cell transplantation setting. Dexrazoxane: (1) The use of dexrazoxane is not routinely recommended for patients with metastatic breast cancer who receive initial doxorubicin-based chemotherapy. (2) The use of dexrazoxane may be considered for patients with metastatic breast cancer who have received a cumulative dosage of 300 mg/m(2) or greater of doxorubicin in the metastatic setting and who may benefit from continued doxorubicin-containing therapy. (3) The use of dexrazoxane in the adjuvant setting is not recommended outside of a clinical trial. (4) The use of dexrazoxane can be considered in adult patients who have received more than 300 mg/m(2) of doxorubicin-based therapy for tumors other than breast cancer, although caution should be used in settings in which doxorubicin-based therapy has been shown to improve survival because of concerns of tumor protection by dexrazoxane. (5) There is insufficient evidence to make a guideline for the use of dexrazoxane in the treatment of pediatric malignancies, with epirubicin-based regimens, or with high-dose anthracycline-containing regimens. Similarly, there is insufficient evidence on which to base a guideline for the use of dexrazoxane in patients with cardiac risk factors or underlying cardiac disease. (6) Patients receiving dexrazoxane should continue to be monitored for cardiac toxicity. Amifostine: (1) Amifostine may be considered for the reduction of nephrotoxicity in patients receiving cisplatin-based chemoth

Non-Hodgkin lymphoma diagnosed from a tracheal window biopsy

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Carboplatin and paclitaxel for previously treated patients with non-small-cell lung cancer

The chemotherapy regimen of paclitaxel and carboplatin produces an objective response in 30%-60% of patients with non-small-cell lung cancer (NSCLC). In a prospective study, we administered paclitaxel 200 mg/m2 (by 1-3-hr infusion) and carboplatin at an area under the plasma concentration curve (AUC) of 5 (by the Calvert formula) every 3 weeks to 21 patients who had previously received predominantly platinum-based chemotherapy for NSCLC. We observed no objective responses. Patients received a median of 2 cycles before disease progression. Three of 5 patients who had received only single-agent treatment with a relatively inactive agent may have had modest clinical benefit. We conclude that the paclitaxel/carboplatin regimen has minimal activity in previously treated patients with NSCLC.

Oat cell carcinoma of the tongue from an unknown primary

Oat cell carcinoma is rarely diagnosed in the head and neck and can be primary or secondary. Primary tumors arise from amine precursor uptake and decarboxylation cells which are found throughout the head and neck. Secondary deposits metastasize most commonly from the lungs. We report a 64-year-old woman with a known pancreatic oat cell carcinoma who came to the ENT Department with dysphagia. On examination, a lesion was seen at the base of the tongue and was histologically an oat cell carcinoma. No treatment was administered and the patient died one month after discharge. This report highlights the difficulty in determining the primary site when a rare tumor metastasizes to the head and neck and no autopsy findings are obtained. To our knowledge, oat cell carcinoma of the tongue has not been previously reported.

The management of asymptomatic firearm injuries in children

Paediatric firearm injuries in the UK are uncommon. We present two children with BB-gun pellets in the parapharyngeal space who were managed conservatively and remained asymptomatic 6 months after the gunshot injury. The management of asymptomatic firearm injuries in children is discussed and a literature review included.

Tuberculous lymphadenopathy masquerading as a bronchial foreign body

A case of recent onset of wheezing with clinical and radiologic findings suggestive of foreign body aspiration is presented. Rigid bronchoscopy revealed an extraluminal compression of the airway. Histopathologic and microbiologic examination revealed tuberculous lymphadenopathy.

Pediatric functional endoscopic sinus surgery: is a second look necessary?

Functional endoscopic sinus surgery (FESS) has become the surgical procedure of choice for the treatment of chronic sinusitis that is refractory to medical treatment. It has become routine to perform endoscopy in children under general anesthesia 2 to 3 weeks after FESS to facilitate examination and cleaning of the operative site. We compared the clinical outcome of 50 children who underwent FESS without a second-look endoscopy with 50 children who underwent a routine second look. Patients with systemic disease (cystic fibrosis, immotile ciliary syndrome, immunoglobulin deficiency) or undergoing a revision procedure were excluded from the study. The results show that the postoperative improvement in nasal obstruction, nasal drainage, and chronic cough was the same for both groups. We conclude that in the vast majority of children without systemic disease and not undergoing a revision procedure, a second endoscopic procedure may not offer any apparent advantage.

Pseudoaneurysm of the right lingual artery: an unusual cause of severe hemorrhage during tonsillectomy

Profuse intraoperative hemorrhage is an uncommon complication of tonsillectomy. We present a three-year-old girl who underwent a routine adenotonsillectomy during which massive bleeding occurred from a large vessel in the right tonsillar fossae. Angiography revealed an aberrant right lingual artery with a pseudoaneurysm. The right lingual artery was embolized with multiple coils and the bleeding was halted. The causes and treatment of extracranial carotid artery pseudoaneurysms are discussed.

Outpatient adenotonsillectomy. Is it safe in children younger than 3 years?

OBJECTIVE

To evaluate the safety of ambulatory adenotonsillectomy in children younger than 3 years.

MATERIALS AND METHODS

The records of 102 children younger than 3 years who underwent adenotonsillectomy as an outpatient procedure were reviewed during a 3-year period.

RESULTS

Ten patients (10%) required overnight hospital admission for an average of 1.4 days. Nine patients were admitted directly from the day-stay unit and 1 patient was admitted 48 hours after surgery. The reason for hospital admission was poor oral intake. None of the patients had postoperative bleeding or respiratory problems or required intensive care unit admission.

CONCLUSION

The safety of ambulatory adenotonsillectomy depends on judicious selection criteria and can be performed in children younger than 3 years.

Subglottic stenosis complicating cardiac surgery in children

OBJECTIVE

To highlight the incidence of subglottic stenosis (SGS) as a complication of surgery for congenital heart disease and the role of single-stage laryngotracheoplasty in treating this complication.

DESIGN

Retrospective case series.

SETTING

University-based referral center specializing in surgery for congenital heart disease and complex airway problem management.

INTERVENTION

Laryngotracheal reconstruction (LTR).

MAIN OUTCOME MEASURE

Successful airway expansion.

RESULTS

At last follow-up, 87.5% (7 of 8) of patients remain free of obstructive airway symptoms.

CONCLUSION

SGS can complicate surgery for congenital heart disease in children. Single-stage LTR is an effective treatment modality for this problem.

Peritonsillar abscess in early childhood. Presentation and management

OBJECTIVE

To highlight the modes of presentation and management of a peritonsillar abscess in children younger than 5 years.

DESIGN

Retrospective case series.

SETTING

Tertiary referral pediatric otolaryngology practice.

PATIENTS

Seven children younger than 5 years.

RESULTS

The mean age of the children studied was 27 months (age range, 7-41 months). Five (71%) of the 7 patients underwent computed tomographic scanning to confirm the diagnosis. Pus was cultured at surgery in every case. The most common organism detected was Streptococcus viridans. The average hospital stay was 72 hours (range, 22 hours to 12 days). After diagnosis of an abscess, all patients underwent an electrocautery tonsillectomy and had an uneventful recovery.

CONCLUSIONS

Children younger than 5 years who present with poor oral intake, high fever, drooling, and trismus should be suspected of having a peritonsillar abscess. A computed tomographic scan of the neck is usually required to confirm a suspected diagnosis. Prompt diagnosis and treatment will lead to a considerable decrease in morbidity. Immediate tonsillectomy is a safe and effective means of abscess drainage.

Relationships between in situ protein degradability and grass developmental morphology

The objective of this research was to determine the relationships between the morphological development and in situ ruminally degradable protein (RDP), ruminally undegradable protein (RUP), and microbial protein of two cool season grasses (intermediate wheatgrass and smooth bromegrass) and two warm season grasses (switchgrass and big bluestem). The initial growth of grass tillers grown near Mead, Nebraska was clipped at ground level six times during the 1992 growing season and morphologically classified. Mean stage was calculated. Forage was ground to pass a 2-mm screen and was incubated in ruminally fistulated steers for 16 h. The RUP was adjusted for microbial protein and acid detergent insoluble N. The mean stage of cool season grasses was higher than that of warm season grasses throughout the growing season. The RDP decreased as plant maturity increased for all species. The RUP expressed as a percentage of crude protein for the cool season grasses was lower than that for warm season grasses. The RUP for intermediate wheatgrass, smooth bromegrass, and switchgrass remained constant across maturities, but RUP for big bluestem decreased as maturity increased. Microbial augmentation of RUP decreased as crude protein decreased in all species. The RUP corrected for acid detergent insoluble N and microbial protein was relatively constant across plant maturities. The quantification of RUP across a range of plant maturities provided information for incorporating RUP content of forage grasses into the diets of animals.

Fat graft myringoplasty in children--a safe and successful day-stay procedure

The surgical closure of dry tympanic membrane perforations in children remains a controversial issue due to conflicting opinions on the appropriate technique, graft material and success rate. We present a review of 342 children who underwent fat graft myringoplasty as a day-stay procedure over a six-year period. Successful closure of the tympanic membrane perforation was achieved in 92 per cent of ears. Subsequent recurrent otitis media with effusion required insertion of ventilation tubes in 12 per cent. No relationship was observed between the age of the child and a successful outcome. We conclude that day-stay fat graft myringoplasty is a safe and successful procedure which results in a dry and safe ear in the majority of children.