排序方式: 共有11条查询结果,搜索用时 15 毫秒
1.
Diane L. Marshall Anna P. Tyler Nathan J. Abrahamson Joy J. Avritt Melanie G. Barnes Leah L. Larkin Juliana S. Medeiros Jerusha Reynolds Marieken G. M. Shaner Heather L. Simpson Satya Maliakal-Witt 《Sexual plant reproduction》2010,23(4):325-336
Although increases in atmospheric [CO2] are known to affect plant physiology, growth and reproduction, understanding of these effects is limited because most studies of reproductive consequences focus solely on female function. Therefore, we examined the effects of CO2 enrichment on male function in the annual Raphanus sativus. Pollen donors grown under elevated [CO2] initially sired a higher proportion of seeds per fruit than ambient [CO2]-grown plants when each was tested against two different standard competitors; however, by the end of the 5-month experiment, these pollen donors sired fewer seeds than ambient [CO2]-grown plants and produced a lower proportion of viable pollen grains. The results of this experiment confirm that elevated [CO2] can alter reproductive success. Additionally, the change in response to elevated [CO2] over time varied among pollen donor families; thus, changes in [CO2] could act as a selective force on this species. 相似文献
2.
To better understand the interaction of physical activity and air pollution exposure, it is important to quantify the change in ventilation rate incurred by activity. In this paper, we describe a method for estimating ventilation using easily-measured variables such as heart rate (HR), breathing rate (fB), and forced vital capacity (FVC). We recruited healthy adolescents to use a treadmill while we continuously measured HR, fB, and the tidal volume (VT) of each breath. Participants began at rest then walked and ran at increasing speed until HR was 160–180 beats per minute followed by a cool down period. The novel feature of this method is that minute ventilation () was normalized by FVC. We used general linear mixed models with a random effect for subject and identified nine potential predictor variables that influence either or FVC. We assessed predictive performance with a five-fold cross-validation procedure. We used a brute force selection process to identify the best performing models based on cross-validation percent error, the Akaike Information Criterion and the p-value of parameter estimates. We found a two-predictor model including HR and fB to have the best predictive performance (/FVC = -4.247+0.0595HR+0.226fB, mean percent error = 8.1±29%); however, given the ubiquity of HR measurements, a one-predictor model including HR may also be useful (/FVC = -3.859+0.101HR, mean percent error = 11.3±36%). 相似文献
3.
Holman DJ Grimes MA Achterberg JT Brindle E O'Connor KA 《American journal of physical anthropology》2006,129(4):609-619
Previous studies of postpartum amenorrhea (PPA) demonstrated distinct subgroups of women with short and long durations of amenorrhea. This phenomenon was attributed to cases where breastfeeding is absent because of pregnancy loss or infant death, or confusion of postpartum bleeding with resumption of menses. We explored these ideas using data from an 11-month prospective study in Bangladesh in which 858 women provided twice-weekly interviews and urine specimens for up to 9 months; 300 women were observed while experiencing PPA. The resulting exact, interval-censored, or right-censored durations were used to estimate parameters of two-component mixture models. A mixture of two Weibull distributions provided the best fit to the observations. The long-duration subgroup made up 84% (+/- 4% SE) of the population, with a mean duration of 457 (+/- 31) days. The short-duration subgroup had a mean duration of 94 (+/- 17) days. Three covariates were associated with the duration of PPA: women whose husbands had high-wage employment had a greater probability of falling in the short-duration subgroup; women in the long-duration subgroup whose husbands seasonally migrated had shorter periods of PPA within the subgroup; and mothers in the short-duration subgroup who gave birth during the monsoon season experienced a shortened duration of PPA within the subgroup. We conclude that the bimodal distribution of PPA reflects biological or behavioral heterogeneity rather than shortcomings of data collection. 相似文献
4.
Sancy A. Leachman Emile Latour Brian Detweiler-Bedell Jerusha B. Detweiler-Bedell Adrienne Zell Elizabeth Wenzel Elizabeth Stoos Jacob H. Nelson Jack Wiedrick Elizabeth G. Berry Jane Lange Ruth Etzioni Jodi A. Lapidus 《Pigment cell & melanoma research》2023,36(6):481-500
Melanoma is a significant cause of cancer death, despite being detectable without specialized or invasive technologies. Understanding barriers to preventive behaviors such as skin self-examination (SSE) could help to define interventions for increasing the frequency of early detection. To determine melanoma knowledge and beliefs across three high-incidence US states, 15,000 surveys were sent to a population-representative sample. We aimed to assess (1) melanoma literacy (i.e., knowledge about melanoma risks, attitudes, and preventive behaviors) and (2) self-reported SSE and its association with melanoma literacy, self-efficacy, and belief in the benefits of SSE. Of 2326 respondents, only 21.2% provided responses indicating high knowledge of melanoma, and 62.8% reported performing an SSE at any time in their lives. Only 38.3% and 7.3% reported being “fairly” or “very” confident about doing SSE, respectively. SSE performance among respondents was most strongly associated with higher melanoma knowledge, higher self-efficacy, and personal history of melanoma. Melanoma literacy among survey respondents was modest, with greater literacy associated with a higher likelihood of reported preventive behavior. This assessment establishes a baseline and provides guidance for public health campaigns designed to increase prevention and early detection of this lethal cancer. 相似文献
5.
Marshall DL Abrahamson NJ Avritt JJ Hall PM Medeiros JS Reynolds J Shaner MG Simpson HL Trafton AN Tyler AP Walsh S 《Annals of botany》2005,95(6):1049-1058
BACKGROUND AND AIMS: Plastic responses to stress in components of reproduction can have important effects on plant fitness and can vary both within and between species. Responses may also depend on when in the life cycle stress occurs. Here, it is predicted that the timing of initiation of a stress, defoliation, would affect the pattern of plastic responses. These differences should occur because some components of reproduction, such as flower number, are determined earlier in a plant's life than others, such as individual seed mass. METHODS: To test this prediction, 50 % artificial defoliation treatments were initiated at four different times for Sesbania macrocarpa and S. vesicaria. Responses were measured in plant size, number of flowers, number of flowers/plant size, fruit set, number of seeds per fruit, individual seed mass and total seed mass per plant. KEY RESULTS: For S. vesicaria, changes in the timing of stress changed the severity, but not the pattern of response. For S. macrocarpa, plastic responses to defoliation varied strikingly between early and late treatments. Late treatments resulted in over-compensation in this species. Sesbania macrocarpa was generally more plastic than S. vesicaria and the species showed opposite responses for most components of reproduction. CONCLUSIONS: While there were effects of timing of defoliation and differences between species, the nature of these effects did not precisely fit our predictions. Our results suggest that differences in the length and flexibility of the life cycles of the two species allowed for unexpected variation in responses. For example, because flower production continued after the last treatment in S. vesicaria, responses were not constrained to reductions in individual seed mass. 相似文献
6.
Jerusha Boyineni Junyoung Kim Beom Sik Kang ChangWoo Lee Sei-Heon Jang 《Biochimica et Biophysica Acta - Proteins and Proteomics》2014,1844(6):1076-1082
Hydrophobic interactions are known to play an important role for cold-adaptation of proteins; however, the role of amino acid residue, Trp, has not been systematically investigated. The extracellular esterase, EstK, which was isolated from the cold-adapted bacterium Pseudomonas mandelii, has 5 Trp residues. In this study, the effects of Trp mutation on thermal stability, catalytic activity, and conformational change of EstK were investigated. Among the 5 Trp residues, W208 was the most crucial in maintaining structural conformation and thermal stability of the enzyme. Surprisingly, mutation of W208 to Tyr (W208Y) showed an increased catalytic site thermal stability at ambient temperatures with a 13-fold increase in the activity at 40 °C compared to wild-type EstK. The structure model of W208Y suggested that Y208 could form a hydrogen bond with D308, which is located next to catalytic residue H307, stabilizing the catalytic domain. Interestingly, Tyr was conserved in the corresponding position of hyper-thermophilic esterases EstE1 and AFEST, which are active at high temperatures. Our study provides a novel insight into the engineering of the catalytic site of cold-adapted enzymes with increased thermal stability and catalytic activity at ambient temperatures. 相似文献
7.
Marshall DL Reynolds J Abrahamson NJ Simpson HL Barnes MG Medeiros JS Walsh S Oliveras DM Avritt JJ 《American journal of botany》2007,94(3):409-418
When more pollen is present on stigmas than needed to fertilize all ovules, selection among pollen grains may occur due to effects of both pollen donors and maternal plants. We asked whether increasing plant age and flower age, two changes in maternal condition, altered the pattern of seed paternity after mixed pollination. We also asked whether changes in seed paternity affected offspring success in an experimental garden. While flower age did not affect seed paternity, there was a dramatic shift in pollen donor performance as plants aged. These differences were seen in the offspring as well, where the offspring of one pollen donor, which sired more seeds on young plants, flowered earlier in the season, and the offspring of another pollen donor, which sired more seeds on old plants, flowered later in the season. Thus, change in maternal condition resulted in altered seed paternity, perhaps because the environment for pollen tube growth was different. The pattern of seed paternity and offspring performance suggests that pollen donors may show temporal specialization. 相似文献
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Systematic Parasitology - Acanthocephalans of the family Polymorphidae Meyer, 1931 are cosmopolitan parasites that infect the intestines of fish-eating birds and mammals. Polymorphid... 相似文献
10.
Sheila K. West Beatriz Munoz Jerusha Weaver Zakayo Mrango Laura Dize Charlotte Gaydos Thomas C. Quinn Diana L. Martin 《PLoS neglected tropical diseases》2016,10(1)