bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential effects of nitrate and ammonium supply on nodule initiation, development, and distribution on roots of pea (Pisum sativum)
Authors: Bollman Mavis I. , Vessey J. Kevin 
Published: August 2006

Low, static concentrations of ammonium have less negative effects on nodulation of pea ( Pisum sativum L.) than nitrate and in some cases may actually stimulate nodulation. Two experiments were carried out to assess the effects of supplying both forms of mineral N, separately and in combination, on nodule initiation, nodule development, nodule distribution between primary and lateral (secondary) roots, tertiary root development, and N2 fixation in pea. Pea plants were grown for up to 24 d after inoculation in hydroponic culture with no mineral N (zero N), NO3– (0.5 mmol·L–1), NH4+ (0.5 mmol·L–1), or NO3– (0.25 mmol·L–1) plus NH4+ (0.25 mmol·L–1). Concentrations of nitrate and ammonium were monitored on a daily basis and held relatively constant by continuous, automatic additions of stock solutions. Pea plants accumulated the most total dry mass (DM) and total N when supplied with the combination of nitrate plus ammonium but had the lowest nodule DM and percentage of nitrogen derived from the atmosphere. Whole-plant nodulation (nodules per plant) and DM-specific nodulation (nodules·g–1 root DM) were 2.3- and 2.4-fold greater, respectively, in pea plants receiving NH4+ at 0.5 mmol·L–1 than in those supplied with NO3– at 0.5 mmol·L–1. The nodulation responses of plants receiving NO3– at 0.25 mmol·L–1 plus NH4+ at 0.25 mmol·L–1 were more similar to those of plants receiving only nitrate than only ammonium, indicating that when both forms of mineral N are available to plants, nitrate has a predominant effect on the nodulation response. Assessment of the stage of development of nodule primordia and nodules during the time course of the experiments indicated that nitrate not only decreased the degree of nodule initiation but also the rate at which those nodules developed. Microscopic observations indicated that the more negative effects of the nitrate treatment on DM-specific nodulation as compared with the ammonium treatment were consistent on both the primary and lateral roots. Quantification of nodulation and tertiary root development on lateral roots indicated that the stimulating effects of ammonium were specific to nodulation; the effects on tertiary root development were different. The study demonstrates for the first time that when both forms of mineral N are available at equal concentrations, the nodulation response in pea is influenced more by nitrate than by ammonium and that the effects of nitrate and ammonium on tertiary root initiation and development are unlike those on nodulation.
PpAG1, a homolog ofAGAMOUS, expressed in developing peach flowers and fruit
Authors: Martin Teresa , Hu Ming , Labbé Hélène , McHugh Sylvia , Svircev Antonet , Miki Brian 
Published: August 2006

MADS-box transcription factors are known to play a central role in floral organ identity and floral meristem determinacy in many gymnosperms and angiosperms. Studies of this nature are limited in fruit tree species despite the economic importance of this group. A peach ( Prunus persica (L.) Batsch) gene, PpAG1, was isolated and shown to be homologous to the Arabidopsis thaliana (L.) Heynh. MADS-box gene AGAMOUS (AG). It is a single gene in peach and codes for a type II or MIKC-type MADS-box protein. The features of the deduced protein sequence indicate that it is similar to other AG homologs from woody plant species. The spatial and developmental patterns of expression parallel those of AG and homologs from other angiosperms with similar floral structures but with some minor differences. In the floral meristem, where AG is responsible for conversion of the vegetative meristem into the floral meristem, the differentiation of the whorls that generate the carpels and stamens coincides with the tissue-specific expression of PpAG1. It continues to be expressed in the ovules, developing fruit and seeds that subsequently develop from the carpels. Constitutive overexpression of PpAG1 in Arabidopsis, using the 35S promoter, caused the homeotic conversion of sepals to carpelloid tissues and altered petal development. This is consistent with C-function genes according to the ABC model of flower development. The data support the conclusion that PpAG1 is the peach homolog of Arabidopsis AG.
Response of red-osier dogwood (Cornus sericea) seedlings to NaCl during the onset of bud break
Authors: Mustard Jennifer , Renault Sylvie 
Published: August 2006

A greenhouse study was designed to test the response of red-osier dogwood (Cornus sericea L.) to NaCl during the onset of bud break. Seedlings treated with 50 mmol·L–1NaCl for 32 d had lower shoot dry mass and shoot height than untreated seedlings. Transpiration and photosynthetic rates, chlorophyll b and carotenoid concentrations of red-osier dogwood seedlings were significantly reduced by NaCl treatment. The shoots of seedlings treated with 50 mmol·L–1NaCl had a higher bulk modulus of cell wall elasticity than those of untreated seedlings, but the water potential components determined from the pressure-volume curves, osmotic potential and pressure potential at full turgor and osmotic potential at pressure loss, suggest that this change did not contribute to salt tolerance. Minor changes, including a small increase in arabinose of the hemicellulose fraction and a decrease in both galactose and rhamnose of the pectin fraction, also occurred in response to NaCl treatment. These changes in cell wall composition and elasticity could be partly attributed to differences in the developmental stage of the shoot tissues resulting from the delay in bud breaking in salt treated plants.
Integrated long-term responses of an arctic–alpine willow and associated ectomycorrhizal fungi to an altered environment
Authors: Clemmensen Karina E. , Michelsen Anders 
Published: August 2006

We evaluated ectomycorrhizal (ECM) colonization and morphotype community composition together with growth response and biomass distribution in the arctic–alpine, prostrate willow Salix herbacea L. × Salix polaris Wahlenb. after 11 seasons of shading, warming, and fertilization at a fellfield in subarctic Sweden. The aim was to assess responses of the integrated plant–fungal system to long-term field experiments simulating expected environmental changes. Warming more than doubled aboveground S. herbacea × S. polaris biomass and shoot growth, whereas shading and nutrient addition had less influence on these variables. In shaded plants, adjustments at leaf level probably buffered major changes in plant biomass allocation. Fertilization increased the root mass fraction and changed root system morphology by decreasing the number of root tips per unit root mass. While no long-term changes in total ECM colonization (%ECM root tips) in response to the treatments were identified, ECM colonization in June just after snowmelt was positively correlated with root density. Changes in densities of potential host plants may therefore be of great importance for ECM colonization intensity in this ecosystem type. The ECM morphotype community changed through the season, and frequencies of some ECM morphotypes ( Cortinarius saturninus and Clavulina spp.) changed more with season than with the treatments. Warming only slightly affected ECM morphotype frequencies, which implies a balanced increase in root tip numbers of most ECM morphotypes in warmed plants. Fertilization changed ECM morphotype community composition mainly because of a decrease in Cenococcum geophilum frequency and an increase in Tomentella stuposa frequency. We hypothesize that a shift from drought stress-tolerant fungi towards a dominance of minerogenic fungi may take place if nutrient availability increases substantially because of anthropogenic disturbances.
Fine-scale vegetation distribution in a cool temperate peatland
Authors: Bubier Jill L. , Moore Tim R. , Crosby Gareth 
Published: August 2006

Carbon (C) modeling and carbon dioxide (CO2) flux measurements in peatlands are dependent on the distribution and productivity of vegetation in a system with a high degree of spatial variability, often linked to the position of the water table. We tested the hypothesis that at a fine-scale (tens of metres) water table position exerts a strong control on species abundance, plant biomass, particularly photosynthetically active tissues, leaf area index (LAI), and areal foliar N and chlorophyll at Mer Bleue, a cool temperate peatland in eastern Canada. Total aboveground biomass ranged from 147 to 1011 g·m–2, with shrubs contributing between 42% and 72% of the total in the transects. We found significant (P < 0.05) positive relationships between foliar and total vascular plant biomass and mean water table position, and significant decreases in the shrub foliar:woody biomass ratio and moss biomass with a lower water table. However, there was no significant relationship between water table position and photosynthetically active tissues (vascular plant leaves and moss capitulum), ranging from 114 to 672 g·m–2) and the areal mass of N in these tissues, ranging from 1.5 to 6.7 g·m–2. Multivariate analyses of vegetation and environmental data showed that species distribution could be explained by both water table and chemistry gradients and that unimodal rather than linear responses best described the species and water table relationships. LAI ranged from 0.1 to over 3 and was correlated with both water table position and with vascular foliar biomass. Percent cover of shrubs was correlated with foliar biomass and LAI. Our results suggest that the less labour-intensive estimates of percent cover can be used to predict the vascular plant foliar biomass and LAI measurements. The lack of relationship between photosynthetically active tissues, tissue N concentrations, and water table may also explain the surprising lack of spatial variability in peak growing season eddy flux net ecosystem CO2exchange in three different areas of the peatland.
Effects of clearcut logging and tree species composition on the diversity and community composition of epigeous fruit bodies formed by ectomycorrhizal fungi
Authors: Durall Daniel M. , Gamiet Sharmin , Simard Suzanne W. , Kudrna Lenka , Sakakibara Stacey M. 
Published: August 2006

The objective of this study was to examine the effects of stand age and tree species composition on the abundance, diversity, and community composition of epigeous fruit bodies formed by ectomycorrhizal (ECM) fungi in the Interior Cedar Hemlock zone of British Columbia. Fruit bodies were collected and identified in May, June, August, September, and October of 1996, 1997, 1998, and 1999 from transects located in new (5 year old) plantations and mature (75–125 year old) wild forests composed of relatively pure Betula papyrifera Marsh. (paper birch), relatively pure Pseudotsuga menziesii var. glauca (Beissn.) Franco (interior Douglas-fir), and mixtures of the two tree species. A total of 187 fungal taxa were collected during the study, of which 185 occurred in mature forests and only 17 occurred in the plantations. Thirty-four taxa were unique to mature predominantly birch forests, 35 were unique to mature predominantly Douglas-fir forests, 17 were unique to mixed mature forests, and 68 taxa were found in all three mature forest types. The abundance of fruit bodies in mature forests varied widely among sampling years and generally increased with annual precipitation. ECM species richness differed between stand ages but not among forest compositions in both plantations and mature forests. Lactarius glyciosmus , Hygrophorus eburneus var. eburneus , and Cortinarius armillatus were more abundant in mature birch than mature Douglas-fir forests. Lactarius torminosus , Leccinum scabrum var. scabrum , and Rozites caperatus were also found predominantly in mature birch and mixed forests, whereas Gomphidius subroseus was more abundant in Douglas-fir forests than in birch and mixed mature forests. Russula brevipes was also found predominantly in mature Douglas-fir and mixed forests. Our results indicate that clearcutting has a profound effect on abundance and composition of ECM fruit bodies, and that changes in forest tree species composition may lead to shifts in ECM fungal community composition.
Impacts of forest fragmentation on the reproductive success of white spruce (Picea glauca)
Authors: O'Connell Lisa M. , Mosseler Alex , Rajora Om P. 
Published: August 2006

The fragmentation of forests into small, isolated remnants may reduce pollen quantity and quality in natural plant populations. The reproductive success of white spruce ( Picea glauca (Moench) Voss) was assessed in a landscape fragmented by agriculture in northern Ontario, Canada. We sampled a total of 23 stands and 104 white spruce trees from three different stand size classes. Each sampled stand was separated by 250–3000 m from the nearest neighbouring stand. Reproductive success, measured as the number of filled seeds per cone, increased with stand size. The total number of seeds per cone, a measure that includes both filled and aborted seeds, also increased with stand size, suggesting that pollen receipt limits the number of seeds in a cone. The proportion of empty seeds (postzygotic abortions) was highest in the two smallest stand size classes, suggesting that inbreeding levels were also highest in these stands. We detected no difference in germination success, seedling growth, and growth of trees up to 10 years from seeds produced by trees from different stand size classes. These results suggest that inbred individuals are largely eliminated during the seed development stage. We estimated that a threshold population size of 180 trees is needed to reduce the negative effects of pollen limitation and inbreeding and maintain seed yields observed in large contiguous stands.
Organic solvents for the glucocorticoid inducer dexamethasone: are they toxic and unnecessary in hydroponic systems?
Authors: Robison Mary M. , Smid Matthew P.L. , Wolyn David J. 
Published: August 2006

Hydroponic cultivation systems provide convenient means of delivering chemical inducers of gene expression to transgenic plants. The glucocorticoid dexamethasone is a water-insoluble inducer and is usually prepared as a stock solution in an organic solvent before addition to the hydroponic nutrient solution. We investigated the effects of ethanol, methanol, and dimethyl sulfoxide (DMSO) on plant appearance and root bacterial growth in nonsterile hydroponic Arabidopsis thaliana (L.) Heynh. culture after 8 d of exposure to the solvent. Ethanol and methanol promoted root bacterial growth and visibly affected overall plant appearance at levels as low as 0.001%, and the effects increased in direct relation to alcohol concentration. DMSO promoted root bacterial growth to a lesser extent than the alcohols and plant appearance was negatively affected only at concentrations of DMSO above 0.01%, suggesting that DMSO may be the best solvent choice. We also demonstrated, however, that dexamethasone prepared as a suspension in water, without dissolution in an organic solvent, was completely effective at inducing transcription of the transgene, thus eliminating the potentially confounding effects of solvents in the interpretation of results.
Differences in Cancer Incidence among Indians in Alaska and New Mexico and U.S. Whites, 1993-2002
Authors: Kelly Janet J. , Lanier Anne P. , Alberts Steven , Wiggins Charles L. 
Published: August 2006

Abstract
Cancer incidence for American Indians and Alaska Natives is typically reported as a single rate for all U.S. indigenous populations combined. Previously reported combined rates suggest that American Indians and Alaska Natives have lower cancer incidence rates compared with the U.S. population. Alaska Native people comprise three major ethnic groups: Eskimo, Indian, and Aleut people. We examined cancer incidence from only Alaska Indians and compared incidence rates with an American Indian population living in New Mexico. These data indicate striking differences in cancer patterns between two American Indian populations. Cancer data for the years 1993 to 2002 for American Indians of New Mexico and U.S. Whites are from the National Cancer Institute Surveillance, Epidemiology, and End Results Program Public-use data set. Data for Alaska Indians are from the Alaska Native Tumor Registry, which is also a Surveillance Epidemiology and End Results Program participant. Overall, cancer incidence rates for all sites combined in New Mexico Indian men and women were lower than U.S. White rates, whereas Alaska Indian men and women exceeded U.S. rates. In comparing Alaska and New Mexico Indians, we observed a 2.5-fold higher incidence of cancer among Alaska Indians. The largest differences between the two Indian populations were noted primarily in cancers associated with tobacco use, including cancers of the oral cavity/pharynx, esophagus (only in men), colon and rectum, pancreas, larynx (men), lung, prostate, and urinary bladder (men). Lung cancer rates in Alaska Indian men and women were 7 and 10 times those of New Mexico Indian men and women. (Cancer Epidemiol Biomarkers Prev 2006;15(8):1515–9)
Tobacco Use in Adult Long-term Survivors of Retinoblastoma
Authors: Foster Meredith C. , Kleinerman Ruth A. , Abramson David H. , Seddon Johanna M. , Tarone Robert E. , Tucker Margaret A. 
Published: August 2006

Abstract
A significant risk of lung cancer was identified among hereditary, but not nonhereditary, retinoblastoma (Rb) patients. Tobacco use was investigated to determine whether differences in smoking prevalence might explain the lung cancer excess and to characterize smoking patterns in adult survivors of Rb. Subjects were 441 hereditary and 395 nonhereditary 1-year survivors of Rb, age ≥18 years, who responded to a telephone survey about current health behavior, including tobacco use. Response rates were 76% for hereditary and 73% for nonhereditary survivors. We compared patterns and predictors of current tobacco use among hereditary and nonhereditary survivors with other childhood cancer survivor studies and the U.S. population. Hereditary Rb survivors currently smoke cigarettes significantly less frequently than nonhereditary survivors (16. 8% versus 24.3%), although among current smokers, age at smoking initiation (17 years old) and average cigarettes (1.5 packs) smoked daily are similar. Predictors of current and ever cigarette smoking include nonhereditary Rb, older age, being female, less education, and use of other tobacco products. Rb survivors smoke cigarettes significantly less than the U.S. population (rate ratio, 0.63; 95% confidence interval, 0.5-0.8 for males; rate ratio, 0.75; 95% confidence interval, 0.6-0.9 for females), but Rb survivors have comparable smoking rates with other childhood cancer survivors. Smoking did not account for the increased risk of lung cancer among hereditary Rb patients, and this may point to an enhanced sensitivity to the carcinogenic effects of tobacco. Adult survivors of Rb should be encouraged to stop smoking. (Cancer Epidemiol Biomarkers Prev 2006;15(8):1464–8)
Merkel Cell Carcinoma and Multiple Primary Cancers
Authors: Howard Regan A. , Dores Graça M. , Curtis Rochelle E. , Anderson William F. , Travis Lois B. 
Published: August 2006

Abstract
Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin for which causative factors remain largely unknown. The site-specific risks of multiple primary cancers associated with MCC, which may provide insight into etiologic influences, have not been quantified in large population-based studies. We estimated the long-term risk of subsequent primary tumors after a first primary MCC (1,306 patients) and the risk of second primary MCC following other first primary cancers (2,048,739 patients) within 11 population-based cancer registries which report to the National Cancer Institute's Surveillance, Epidemiology, and End Results Program (1986-2002). Patients with first primary MCC were at significantly increased risk of developing a subsequent cancer [standardized incidence ratio (SIR), 1.22; 95% confidence intervals (95% CI), 1.01-1.45; observed (O = 122)], with significant excesses restricted to the first year after diagnosis (SIR, 1.71; 95% CI, 1.21-2.33; O = 39). Significantly elevated site-specific risks were observed for cancers of salivary gland (SIR, 11.55; 95% CI, 2.32-33.76; O = 3), biliary sites other than liver and gallbladder (SIR, 7.24; 95% CI, 1.46-21.16; O = 3), and non–Hodgkin lymphoma (SIR, 2.56; 95% CI, 1.23-4.71; O = 10). Nonsignificantly increased risks of 2-fold or higher were seen for chronic lymphocytic leukemia, and cancers of the small intestine and brain. A significantly increased 1.36-fold risk (95% CI, 1.19-1.55; O = 221) of MCC as a second primary malignancy was observed among patients with all other first primary cancers taken together. In particular, significant 3- to 7-fold excesses of MCC followed multiple myeloma (SIR, 3.70; 95% CI, 1.01-9.47; O = 4), chronic lymphocytic leukemia (SIR, 6.89; 95% CI, 3.77-11.57; O = 14), non–Hodgkin lymphoma (SIR, 3.37; 95% CI, 1.93-5.47; O = 16), and malignant melanoma (SIR, 3.05; 95% CI, 1.74-4.95; O = 16). Although enhanced medical surveillance may play a role, increased reciprocal risks suggest that MCC may share etiologic influences with other malignancies. Heightened awareness of the associations of lymphohematopoietic malignancies with MCC may facilitate early clinical recognition. (Cancer Epidemiol Biomarkers Prev 2006;15(8):1545–9)
Validity and Reliability of Adult Recall of Past Sun Exposure in a Case-Control Study of Multiple Sclerosis
Authors: van der Mei I.A.F. , Blizzard L. , Ponsonby A-L. , Dwyer T. 
Published: August 2006

Abstract
Background: Measurement of past sun exposure through recall by adults has the potential for measurement error. We aimed to investigate aspects of validity and reliability of self-reported past sun exposure.
Methods: A population-based case-control study was conducted in Tasmania on 136 cases with multiple sclerosis and 272 age- and sex-matched community controls. Repeat interviews on 52 cases and 52 controls were done on average 11 weeks after the initial interview. Sun exposure was assessed by questionnaire and lifetime calendar. Other measurements included serum 25-hydroxyvitamin D, actinic damage, and skin phenotype.
Results: There was an association between recent sun exposure and serum vitamin D (time in the sun: r = 0.22, P &lt; 0.01; activities outside: r = 0.31, P &lt; 0.01 for controls) and between lifetime sun exposure and actinic damage [correlation between 0.34 (P &lt; 0.01) and 0.17 (P = 0.01) for controls]. The test-retest weighted κ statistic of self-reported sun exposure ranged from 0.43 to 0.74. Recall of childhood/adolescent sun exposure by standardized questioning was no less reproducible than recall of recent adult sun exposure and no less reliable when made with the calendar method. Comparing the questionnaire and calendar method, the measures of childhood/adolescent sun exposure had a similar predictive validity for multiple sclerosis.
Conclusions: The results of this study provide further evidence that adults are able to recall past sun exposure with shown validity and reliability and present information about the possible reasons for the good reliability of recalled sun exposure measures. (Cancer Epidemiol Biomarkers Prev 2006;15(8):1538–44)