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The Function of Urease in Citrullus Seeds 总被引:1,自引:0,他引:1
Urease is present in considerable quantity in the cotyledonsof Citrullus, though elsewhere in the plant it is present onlyin traces or is absent; urease activity in the cotyledons changesduring growth, showing an initial rise followed by an abruptdrop almost to zero. These changes, under a wide variety ofconditions, are not correlated with those in the major nitrogenfractions; they are, however, closely correlated with cell extensionand the associated changes in water content and respiration.A connexion with chlorophyll formation is possible but unlikely.It is suggested that the changes in cotyledonary urease constitutemerely one aspect of the protoplasmic differentiationthat takes place as a cell matures. 相似文献
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Sorption and desorption experiments were performed by the batch method on the B horizons of five natural soils: Umbric Cambisol, Endoleptic Luvisol, Mollic Umbrisol, Dystric Umbrisol, and Dystric Fluvisol. Individual and competitive sorption and desorption capacity and hysteresis were determined. The results showed that Pb2+ was sorbed and retained in a greater quantity than Cd2+ and that the hysteresis of the first was greater than that of the second. The most influential characteristics of the sorption and retention of Pb2+ were pH, ECEC, Fe and Mn oxides and clay contents. For Cd2+ they were mainly pH and, to a lesser extent, Mn oxides and clay content. The combined use of TOF-SIMS, FE-SEM/EDS and sorption and desorption analyses was suitable for achieving a better understanding of the interaction between soil components and the two heavy metals. They show the preferential association of Pb2+ with vermiculite, chlorite, Fe and Mn oxides, and of Cd2+ with the same components, although to a much lesser extent and intensity. This was due to the latter’s higher mobility as it competed unfavourably with the Pb2+ sorption sites. TOF-SIMS and FE-SEM/EDS techniques confirmed the results of the sorption experiments, and also provided valuable information on whether the soil components (individually or in association) retain Cd2+ and / or Pb2+; this could help to propose effective measures for the remediation of contaminated soils. 相似文献
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Júlia Graciele Vieira Geandre de Carvalho Oliveira Guimes Rodrigues Filho Rosana Maria Nascimento de Assuno Carla da Silva Meireles Daniel Alves Cerqueira Wanderly Geraldo Silva Leila Aparecida de Castro Motta 《Carbohydrate polymers》2009,78(4):779-783
In previous works, methylcellulose (MC) was prepared from sugarcane bagasse cellulose in heterogeneous medium using dimethyl sulfate (DMS) as etherification agent. MC was produced in a range of degrees of substitution (DS) from 0.70 to 1.40 and the materials showed low water solubility. In this work methylcellulose was prepared with 5 h (MC5h) of reaction with reagent substitution at each hour. MC5h showed a DS of 1.89 ± 0.04. An aqueous viscous suspension was produced with MC5h for application as viscosity enhancing admixture of cimentitious adhesive mortars. It was observed a 40.37% increase on the consistency index (CI) and a 27.70% increase on the Potential Tensile Adhesion Strength. Such characteristics show the potential of this material for the utilization in situations that require good workability, improve viscosity and adhesive properties such as for tile setting in civil engineering. 相似文献
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Leonardo da Cunha Menezes Souza Eneida de Moraes Marcílio Cerqueira 《Electromagnetic biology and medicine》2014,33(2):98-102
Transmission and reception of mobile telephony signals take place through electromagnetic wave radiation, or electromagnetic radiofrequency fields, between the mobile terminal and the radio base station. Based on reports in the literature on adverse effects from exposure to this type of radiation, the objective of this study was to evaluate the genotoxic and cytotoxic potential of such exposure, by means of the micronucleus test on exfoliated cells from the oral epithelium. The sample included 45 individuals distributed in 3 groups according to the amount of time in hours per week (t) spent using mobile phones: group I, t?>?5?h; group II, t?>?1?h and ≤?5?h; and group III, t?≤?1?h. Cells from the oral mucosa were analyzed to assess the numbers of micronuclei, broken egg structures and degenerative nuclear abnormalities indicative of apoptosis (condensed chromatin, karyorrhexis and pyknosis) or necrosis (karyolysis in addition to these changes). The occurrences of micronuclei and degenerative nuclear abnormalities did not differ between the groups, but the number of broken egg (structures that may be associated with gene amplification) was significantly greater in the individuals in group I (p?0.05). 相似文献