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91.
Pereira JR 《Science (New York, N.Y.)》1924,60(1544):102-103
92.
A developmentally regulated neuraminidase activity in Trypanosoma cruzi 总被引:18,自引:0,他引:18
M E Pereira 《Science (New York, N.Y.)》1983,219(4591):1444-1446
The human pathogen Trypanosoma cruzi (Y strain) contains a neuraminidase activity that varies widely in the different developmental stages of the parasite. The specific neuraminidase activity of infective trypomastigotes obtained from tissue culture and from the bloodstream of infected mice is 7 to 15 times higher than that of the acellular culture forms. Amastigotes were devoid of enzyme activity. The enzyme has a pH optimum of 6.0 to 6.5. Live trypanosomes released sialic acid from human erythrocytes and plasma glycoproteins. Several sialyl compounds were hydrolyzed by the parasite, but the best substrate was the protein orosomucoid. Erythrocytes from infected mice with T. cruzi parasitemia were agglutinated by peanut lectin and the hemagglutination titer was correlated with the degree of parasitemia. 相似文献
93.
Marimuthu MP Jolivet S Ravi M Pereira L Davda JN Cromer L Wang L Nogué F Chan SW Siddiqi I Mercier R 《Science (New York, N.Y.)》2011,331(6019):876
Cloning through seeds has potential revolutionary applications in agriculture, because it would allow vigorous hybrids to be propagated indefinitely. However, asexual seed formation or apomixis, avoiding meiosis and fertilization, is not found in the major food crops. To develop de novo synthesis of apomixis, we crossed Arabidopsis MiMe and dyad mutants that produce diploid clonal gametes to a strain whose chromosomes are engineered to be eliminated after fertilization. Up to 34% of the progeny were clones of their parent, demonstrating the conversion of clonal female or male gametes into seeds. We also show that first-generation cloned plants can be cloned again. Clonal reproduction through seeds can therefore be achieved in a sexual plant by manipulating two to four conserved genes. 相似文献
94.
Gustavo R. Rodríguez Javier H. Pereira da Costa Damian D. Tomat Guillermo R. Pratta Roxana Zorzoli Liliana A. Picardi 《Scientia Horticulturae》2011
The tomato fruit quality results of biochemical and physiological changes that occur during the ripening process. Although, the pericarp total protein profiles are less polymorphic than DNA-based markers the polymorphism in those could be directly associated with fruit quality traits. The aim of this work was to identify associations between polymorphic polypeptides from fruit pericarp at two ripening stages and fruit quality traits evaluated in two segregating populations of tomato. A cross between a normal ripening cultivar of Solanum lycopersicum (C, Caimanta) and a genotype carrying the nor (non ripening) gene (N) as well as a cross between Caimanta and a cherry type tomato of S. lycopersicum var. cerasiforme (Ce) showed genetic variance for several fruit quality traits such as fruit weight, shape, solids soluble content, acidity, color and fruit shelf life. The quantitative variations observed at phenotypic level had correspondence with the polymorphism detected in the protein profiles. Indeed, the polymophic polypeptides associated with quality fruit traits and fruit shelf life would be useful to assist tomato breeding programs as protein molecular markers. 相似文献
95.
Luís?Borda-de-águaEmail author Laetitia?Navarro Catarina?Gavinhos Henrique?M.?Pereira 《Landscape Ecology》2011,26(2):253-265
Roads can have drastic impacts on wildlife populations. Although there is wide recognition of the negative impacts caused
by roads and a wealth of practical studies, there is a lack of theoretical work that can be used to predict the impact of
road networks or to implement mitigation measures. Here, using Skellam’s diffusion model, we develop analytic and numerical
approaches to analyze the impact of road networks on the survival of populations. Our models show that the viability of a
population is determined not only by road density but also by the size and shape of patches. Accordingly, we studied the minimum
size of a patch to sustain a population with given diffusion and growth parameters. We provide simple formulas to estimate
the minimum patch size, and illustrate the importance of shape with square and rectangular patches. Our models also allow
the estimation of time to extinction after road construction for a population in a patch smaller than that of the minimum
size. Finally, using numerical computations we illustrate how the spatial arrangement of fences strongly affects both the
equilibrium density and the spatial distribution of populations, and that not all fence layouts are equally effective. We
anticipate that our methods provide a tool to assess the impact of geometrical features of road networks on wildlife and that
they can be used to design mitigation measures to prevent the decline and extinction of populations in an anthropogenically
disturbed landscape. 相似文献
96.
Sofia Knapic Isabel Pinto Seppä Arto Usenius Helena Pereira 《European Journal of Forest Research》2011,130(5):745-751
Recent research is underway to study cork oak (Quercus suber L.) wood potential for production of wood components. A total of 35 stems of young and mature cork oaks were sampled, live sawn into flitches, scanned using VTT’s WoodCIM®, and the measured data computed by VTT’s PuuPilot software, allowing stem 3D reconstruction. Sawing simulations were run for 0.5 m and 1 m logs and the whole stem. Sawn products were (1) planks, (2) parquet, (3) lamparquet, and (4) external component of multilayer planks. Cork oak stems showed a moderate to small taper (mean 24 mm/m). Curviness varied between straight to significantly crooked stems (mean value 40 mm) Batch yields for the tested products ranged 25–43% and 37–50% for 0.5 m logs of young and mature trees, respectively; for 1 m logs, batch yields ranged 19–41% and 25–54%. When using the whole stem, batch yields were lower, ranging 11–38% and 15–50%. Higher yields were obtained for all log lengths and samples for production of lamparquet, parquet, and multilayer component. 相似文献
97.
98.
99.
Objective To compare intraocular pressure (IOP) measurements made on healthy adult rabbits without the effect of tranquilizers using the new applanation tonometer, Tono‐Pen Avia®, and the rebound tonometer Tonovet®. Methods Intraocular pressure was measured throughout the day (6:00, 9:00, 12:00, 15:00, and 18:00 h) in 38 adult New Zealand White rabbits (76 eyes). The animals were 20 males and 18 females, with a mean weight of 3.5 kg and an average age of 6 months. A complete ocular exam (including Schirmer tear test, fluorescein staining, slit‐lamp biomicroscopy, and direct ophthalmoscopy) was performed on all animals at the beginning of the trial. Rebound tonometry was performed, and after 10 min, anesthetic drops were instilled and applanation tonometry was carried out. IOP values obtained using the two techniques were analyzed statistically. Results The mean IOP was 9.51 ± 2.62 mmHg with Tonovet®, and 15.44 ± 2.16 mmHg with the Tono‐Pen Avia®. Significant differences between measurements with the two tonometers were observed (P < 0.001). The linear regression equation describing the relationship between the two tonometers was y = 0.4923x + 10.754 (y = Tonovet® and x = Tono‐Pen Avia®). High IOPs were recorded in the early measurements (6:00), but the average IOPs from both devices were statistically similar throughout the day (P = 0.086). The correlation coefficient was r2 = 0.357. No significant difference in IOP regarding gender was observed. Conclusion The Tono‐Pen Avia® recorded higher levels of IOP compared with the Tonovet®. Early in the day, the IOP of rabbits was higher than later in the day, regardless of the tonometer used. 相似文献
100.
Rosanna S. Valitutto Silvia M. Sella Emmanoel V. Silva-Filho Roberto Guimarães Pereira Norbert Miekeley 《Water, air, and soil pollution》2007,178(1-4):89-102
Aquatic macrophytes are well known accumulators for heavy metals, the reason why they are used as bioindicators for water quality and in phytoremediaton strategies. This study reports on the elemental concentrations in four free-floating aquatic macrophytes (S. auriculata; P. stratiotes; E. crassipes and E. azurea) growing in two water reservoirs (Santana e Vigário, Rio de Janeiro State, Brazil) of an electric power plant that receive input from the polluted Paraíba do Sul River. Filtered water samples and water suspended solids from these environments were also analysed. Inductively coupled plasma mass spectrometry was used as the principal method, allowing the determination of up to 41 elements, including the rare-earth elements (REEs) and other trace metals not assayed before in these macrophytes. The results show that all elements studied are accumulated by the macrophytes with concentration ratios (CR = [plant]: [water]) varying from about 1,000 to 200,000, based on the dry weight of the plant species. With a few exceptions, highest accumulations were observed in E. crassipes in which CRs increase in the sequence: Cu < Mo < Cr < Pb < Tl < Fe < La < Zn < Ce< Mn. Surprisingly high CRs (e.g. Ce: 74,000) and corresponding mass concentrations were observed for the rare-earth elements (e.g. ∑REE: 112 mg kg?1), also measured in the water suspended particle fraction. The results show that this fraction acts as an effective sink for trace metals in the aquatic system studied and seems to play also an important role in the transfer of metals from water to the plant species. 相似文献