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排序方式: 共有161条查询结果,搜索用时 15 毫秒
1.
Nitrogen losses from perennial grass species 总被引:1,自引:0,他引:1
Nitrogen losses from plants may occur through a variety of pathways, but so far, most studies have only quantified losses of nutrients by above-ground litter production. We used 15N pulse labelling to quantify total nitrogen losses from above- and below-ground plant parts. Using this method we were able to include also pathways other than above-ground litter production. To test the hypothesis that species from nutrient-poor habitats lose less nitrogen than species from more fertile soils, six perennial grasses from habitats with a wide range of nutrient availability were investigated: Lolium perenne, Arrhenatherum elatius, Anthoxanthum odoratum, Festuca rubra, F. ovina and Molinia caerulea. The results of an experiment carried out in pots in a green-house at two fertility levels show that statistically significant losses occur through pathways other than above-ground litter production. In the low fertility treatment, most (70%) losses from L. perenne occurred by litter production, but in Ar. elatius, F. rubra, F. ovina and M. caerulea, more than 50% of labelled N losses took place by root turn-over, leaching or exudation from roots. When nutrient supply increased, the 15N losses in above-ground dead material increased in all species and in Ar. elatius, A. odoratum and F. rubra the 15N losses via other pathways decreased. Ranked according to decreasing turnover coefficient the sequence of species was: L. perenne, A. odoratum, F. rubra, F. ovina, Ar. elatius, M. caerulea. These results suggest that species adapted to sites with low availability of nutrients lose less nitrogen (including above- and below-ground losses) than species adapted to more fertile soils. 相似文献
2.
Marta Castro Lizet Sánchez Dennis Pérez Carlos Sebrango Ziv Shkedy Patrick Van der Stuyft 《PloS one》2013,8(12)
The reemergence of dengue as an important public health problem reflects the difficulties in sustaining vertically organized, effective, control programs and the need for community-based strategies for Aedes aegypti control that result in behavioral change. We aimed to disentangle the relationships between underlying determinants of dengue related practices. We conducted a cross-sectional study in 780 households in La Lisa, Havana, Cuba. A questionnaire and an observation guide were administrated to collect information on variables related to economic status, knowledge on dengue, risk perception and practices associated with Aedes aegypti breading sites. To test a conceptual model that hypothesized direct relationships among all these constructs, we first used Exploratory Factor Analysis with Principal Component Analysis to establish the relationship between observed variables and the underlying latent variables. Subsequently, we tested whether the observed data supported the conceptual model through Confirmatory Factor Analysis. Exploratory Factor Analysis indicated that the items measured could be reduced into five factors with an eigenvalue >1.0: Knowledge on dengue, Intradomiciliar risk practices, Peridomiciliar risk practices, Risk perception and Economic status. The proportion of the total variance in the data explained by these five factors was 74.3%. The Confirmatory Factor Analysis model differed from our hypothesized conceptual model. Only Knowledge on dengue had a significant, direct, positive, effect on Practices. There was also a direct association of Economic status with Knowledge on dengue, but not with Risk perception and Practices. Clarifying the relationship between direct and indirect determinants of dengue related practices contributes to a better understanding of the potential effect of Information Education and Communication on practices and on the reduction of Aedes aegypti breeding sites and provides inputs for designing a community based strategy for dengue control. 相似文献
3.
The 14-3-3 protein family interacts with more than 2000 different proteins in mammals, as a result of its specific phospho-serine/phospho-threonine binding activity. Seven paralogs are strictly conserved in mammalian species. Here, we show that during adipogenic differentiation of 3T3-L1 preadipocytes, the level of each 14-3-3 protein paralog is regulated independently. For instance 14-3-3β, γ, and η protein levels are increased compared to untreated cells. In contrast, 14-3-3ε protein levels decreased after differentiation while others remained constant. In silico analysis of the promoter region of each gene showed differences that explain the results obtained at mRNA and protein levels. 相似文献
4.
5.
Cdc15 is required for spore morphogenesis independently of Cdc14 in Saccharomyces cerevisiae 下载免费PDF全文
Pablo-Hernando ME Arnaiz-Pita Y Nakanishi H Dawson D del Rey F Neiman AM Vázquez de Aldana CR 《Genetics》2007,177(1):281-293
In Saccharomyces cerevisiae exit from mitosis requires the Cdc14 phosphatase to reverse CDK-mediated phosphorylation. Cdc14 is released from the nucleolus by the Cdc14 early anaphase release (FEAR) and mitotic exit network (MEN) pathways. In meiosis, the FEAR pathway is essential for exit from anaphase I. The MEN component Cdc15 is required for the formation of mature spores. To analyze the role of Cdc15 during sporulation, a conditional mutant in which CDC15 expression was controlled by the CLB2 promoter was used. Cdc15-depleted cells proceeded normally through the meiotic divisions but were unable to properly disassemble meiosis II spindles. The morphology of the prospore membrane was aberrant and failed to capture the nuclear lobes. Cdc15 was not required for Cdc14 release from the nucleoli, but it was essential to maintain Cdc14 released and for its nucleo-cytoplasmic transport. However, cells carrying a CDC14 allele with defects in nuclear export (Cdc14-DeltaNES) were able to disassemble the spindle and to complete spore formation, suggesting that the Cdc14 nuclear export defect was not the cause of the phenotypes observed in cdc15 mutants. 相似文献
6.
Denise Arico Martina Legris Luciana Castro Carlos Fernando Garcia Aldana Laino Jorge Jos Casal Maria Agustina Mazzella 《Plant, cell & environment》2019,42(9):2554-2566
Due to the preeminence of reductionist approaches, understanding of plant responses to combined stresses is limited. We speculated that light‐quality signals of neighbouring vegetation might increase susceptibility to heat shocks because shade reduces tissue temperature and hence the likeness of heat shocks. In contrast, plants of Arabidopsis thaliana grown under low‐red/far‐red ratios typical of shade were less damaged by heat stress than plants grown under simulated sunlight. Neighbour signals reduce the activity of phytochrome B (phyB), increasing the abundance of PHYTOCHROME‐INTERACTING FACTORS (PIFs). The phyB mutant showed high tolerance to heat stress even under simulated sunlight, and a pif multiple mutant showed low tolerance under simulated shade. phyB and red/far‐red ratio had no effects on seedlings acclimated with nonstressful warm temperatures before the heat shock. The phyB mutant showed reduced expression of several fatty acid desaturase (FAD) genes and less proportion of fully unsaturated fatty acids and electrolyte leakage of membranes exposed to heat shocks. Red‐light‐activated phyB also reduced thermotolerance of dark‐grown seedlings but not via changes in FADs expression and membrane stability. We propose that the reduced photosynthetic capacity linked to thermotolerant membranes would be less costly under shade, where the light input limits photosynthesis. 相似文献
7.
Margarita Medina‐Romero Andrew O'Reilly‐Nugent Anthony Davidson Jonathan Bray Elizabeth Wandrag Bernd Gruber Angelica Lopez‐Aldana Rakhi Palit Tim Reid Aaron Adamack Rod Pietsch Chris Allen Ralph Mac Nally Richard P. Duncan 《Ecography》2019,42(9):1514-1522
Imperfect detection can bias estimates of site occupancy in ecological surveys but can be corrected by estimating detection probability. Time‐to‐first‐detection (TTD) occupancy models have been proposed as a cost–effective survey method that allows detection probability to be estimated from single site visits. Nevertheless, few studies have validated the performance of occupancy‐detection models by creating a situation where occupancy is known, and model outputs can be compared with the truth. We tested the performance of TTD occupancy models in the face of detection heterogeneity using an experiment based on standard survey methods to monitor koala Phascolarctos cinereus populations in Australia. Known numbers of koala faecal pellets were placed under trees, and observers, uninformed as to which trees had pellets under them, carried out a TTD survey. We fitted five TTD occupancy models to the survey data, each making different assumptions about detectability, to evaluate how well each estimated the true occupancy status. Relative to the truth, all five models produced strongly biased estimates, overestimating detection probability and underestimating the number of occupied trees. Despite this, goodness‐of‐fit tests indicated that some models fitted the data well, with no evidence of model misfit. Hence, TTD occupancy models that appear to perform well with respect to the available data may be performing poorly. The reason for poor model performance was unaccounted for heterogeneity in detection probability, which is known to bias occupancy‐detection models. This poses a problem because unaccounted for heterogeneity could not be detected using goodness‐of‐fit tests and was only revealed because we knew the experimentally determined outcome. A challenge for occupancy‐detection models is to find ways to identify and mitigate the impacts of unobserved heterogeneity, which could unknowingly bias many models. 相似文献
8.
Arturo A. Vitale Carina C. Ferrari Hernán Aldana Jorge M. Affanni 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,681(2):381
In the present study a new chromatographic method was developed to quantify melatonin in rat pineal that can be extended to other tissues. Melatonin was extracted from an acid homogenate with ethyl acetate to avoid amine interference. HPLC was performed with silica normal-phase column and fluorescence detection. This method is sensitive enough for detecting melatonin in a single pineal gland with a detection limit of 3 pg/mg tissue. 相似文献
9.
Llanes R González M Martínez I Sosa J Guzmán D Gutiérrez O Llop A Sánchez L 《Memórias do Instituto Oswaldo Cruz》2003,98(8):1089-1091
Four methods (chromogenic, acidimetric, inhibition, and iodometric) for demonstration of the beta-lactamase production by 70 isolates of Neisseria gonorrhoeae, were evaluated in Cuba. There was 100% correlation between all beta-lactamase methods and the standardized penicillin dilution susceptibility test for penicillinase-non-producing N. gonorrhoeae. For penicillinase-producing N. gonorrhoeae strains, there was a perfect correlation between the chromogenic method and penicillin susceptibility testing, but one and two strains failed to give a positive result for beta-lactamase with the inhibition/acidimetric and the iodometric methods, respectively. There was a high concordance between the chromogenic method, considered as gold standard and the rest of penicillinase tests evaluated: Kappa Index (KI) = 0.98 for inhibition/acidimetric methods and KI = 0.97 for the iodometric method. The four methods evaluated were accurate, reproducible, easily readable, economical, and ease to use for screening primary isolates of N. gonorrhoeae in Cuba. We recommended the use of the inhibition method, when testing the penicillinase activity in gonococcal isolates in provincial and municipal reference laboratories. 相似文献
10.
The Mexican oyster fishery, 90% supported by the coastal lagoons of the Gulf of Mexico, has decreased drastically in the last six years as a result of anthropogenic pollution and improper management. The mussel Ischadium recurvum has proliferated and competes with oysters for space and probably food. Crassostrea virginica and Ischadium recurvum were studied to evaluate somatic production with biometry and physiological condition indices (PCI's) during an annual cycle. A random sample of 200 organisms was taken montly for each species. Condition indices wet flesh weigth: wet shell weight ratio (WFW/WSW), dry flesh weight: wet flesh weight ratio (DFW/WFW), dry flesh wet: dry shell weight ratio (DFW/DSW), and ash free dry weight: tissue dry weight (AFDW/TDW) were calculated. In order to stablish physiological condition and temporal variability, these indices were compared between species and months. The somatic production of mussels was higher than in oysters. This enhancement in production could be explained by: 1) Mussel uses less energy for shell production, 2) a constant recruitment of mussel almost year-round, and 3) the mesohalin lagoon was more favourable to the mussel. 相似文献