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991.
Inter-specific differences in seedling survival responses along a sun-shade gradient and the influence of low-water availability were examined for four Iberian tree species (Quercus robur L., Quercus pyrenaica Willd., Pinus sylvestris L. and Pinus pinaster Ait.) typical of the cool temperate–Mediterranean transition zone. Seedlings were grown under controlled conditions in a factorial experiment with four levels of irradiance (1%, 6%, 20% and 100% of full sunlight) and two levels of water availability. Five censuses (from late spring to autumn) leading to four regular intervals (T0 → TI; TI → TII; TII → TIII; TIII → TIV) were established. Statistical models of seedling survival as a function of irradiance were calibrated throughout the whole experiment (T0 → TIV) and also for each time interval and water availability level. Seedling survival responses among different species diverged both in the type of functional response to irradiance and in their response to water stress. Ranking of species according to shade tolerance (Q. pyrenaica > Q. robur > P. sylvestris > P. pinaster) contrasted with tolerance of high irradiance and conformed to a hypothetical sun-shade trade-off for survival (i.e. species having higher survival in low irradiance—oaks—had poorer survival at high irradiance and vice-versa). Low-water availability also differentially affected each species, with pines being more drought tolerant than oaks. At an intra-specific level, low-water availability decreased survival of Q. pyrenaica under both high and low irradiance. For Q. robur, however, low-water availability exerted a relatively stronger effect under low irradiance. Consequences of the interplay between irradiance and water availability for explaining segregation and coexistence of forest tree species at the ecotone between cool temperate and Mediterranean forests are discussed. 相似文献
992.
993.
The fungal entomopathogen Beauveria bassiana became established as an endophyte in coffee seedlings grown in vitro and inoculated with B. bassiana suspensions in the radicle. The fungus was recovered as an endophyte 30 and 60 days postinoculation, from stems, leaves,
and roots, and at 60 days postinoculation one of the isolates was also recovered as an epiphyte. Fusarium sp., Rhodotorula sp., and four bacterial morpho-species were also detected, indicating these were present as endophytes in the seed. 相似文献
994.
Dondero F Rossi T Delfino M Imbrogno N Cannistrà S Mazzilli F 《Cell and tissue banking》2006,7(1):61-64
The aim of our study was to evaluate the bio-kinetic characteristics of human semen refrigerated for different periods and
to compare the effects of refrigeration at +4 °C against cryopreservation of human sperm at −196 °C. Semen was obtained from
30 male partners of infertile couples (infertile subjects) with the following semen profile: sperm count ≥10 × 106/ml; progressive motility ≥20%; atypical forms <70% and white blood cells <1.0 × 106/ml. Fifteen normospermic subjects were also selected as controls (control subjects). The following tests were carried out
on basal, refrigerated and cryopreserved sperm: a) sperm kinetic properties (by Superimposed Image Analysis System); b) the
Hypoosmotic Viability Test (HVT) (combined Hypoosmotic Swelling and Viability Test). The results of the study showed that
the percentage recovery of kinetic properties and of HVT were optimum for up to 48 h. After refrigeration for 72 h, a drastic
decrease in straight motility recovery was observed. No significant differences were observed between cryopreservation and
refrigeration at +4 °C for 48 h for motility or HVT recoveries in samples from control subjects. However, in infertile subjects,
a significant decrease in straight progressive motility and HVT recoveries was observed in cryopreserved samples compared
to those refrigerated for 48 h. Neither refrigeration nor cryopreservation led to the growth of pathogenic bacteria in any
of the cases studied. Based on the above results, refrigeration could represent a useful alternative to the cryopreservation
method. 相似文献
995.
The resistance to experimental, highly frequent disturbance has been analysed in three congeneric, strong-resprouter species
(Erica australis, E. scoparia and E. arborea) that co-occur in heath-dominated communities of the northern side of the Strait of Gibraltar, southern Spain. To do so,
mature individuals of the three species from a long undisturbed location were clipped at the ground level every sixth month
during two years. The relationship between the resprouted biomass dry weight (as indicative of the resprouting vigour) and
the upper surface area of the lignotuber along the experiment was established separately for each species at each clipping
event by means of linear regressions analysis. The resprouting vigour of the three species was compared by means of independent
one-way ANOVAs within each clipping event. Resprouting vigour decreased after recurrent clippings in the three species. Nevertheless,
significant differences between species in this loss of resprouting vigour were detected, being E. scoparia the most resistant to the experimental, highly frequent clipping. It is concluded that experimental levels of recurrent disturbance
may help to find out differences in resilience within similar (taxonomically, morfologically and/or ecologically), strong-resprouter
plant species. Considering the history of forestry management in the nothern side of the Strait of Gibraltar, differences
in this regard between the three Erica species may contribute to explain their somewhat segregated ecological distribution in this region. 相似文献
996.
Peralta RA Neves A Bortoluzzi AJ Dos Anjos A Xavier FR Szpoganicz B Terenzi H de Oliveira MC Castellano E Friedermann GR Mangrich AS Novak MA 《Journal of inorganic biochemistry》2006,100(5-6):992-1004
The new homodinuclear complexes, [Cu(2)(II)(HLdtb)(mu-OCH(3))](ClO(4))(2) (1) and [Cu(2)(II)(Ldtb)(mu-OCH(3))](BPh(4)) (2), with the unsymmetrical N(5)O(2) donor ligand (H(2)Ldtb) - {2-[N,N-Bis(2-pyridylmethyl)aminomethyl]-6-[N',N'-(3,5-di-tert-butylbenzyl-2-hydroxy)(2-pyridylmethyl)]aminomethyl}-4-methylphenol have been synthesized and characterized in the solid state by X-ray crystallography.In both cases the structure reveals that the complexes have a common {Cu(II)(mu-phenoxo)(mu-OCH(3))Cu(II)} structural unit.Magnetic susceptibility studies of 1 and 2 reveal J values of -38.3 cm(-1) and -2.02 cm(-1), respectively, and that the degree of antiferromagnetic coupling is strongly dependent on the coordination geometries of the copper centers within the dinuclear {Cu(II)(mu-OCH(3))(mu-phenolate)Cu(II)} structural unit.Solution studies in dichloromethane, using UV-Visible spectroscopy and electrochemistry, indicate that under these experimental conditions the first coordination spheres of the Cu(II) centers are maintained as observed in the solid state structures, and that both forms can be brought into equilibrium ([Cu(2)(HLdtb)(mu-OCH(3))](2+)=[Cu(2)(Ldtb)(mu-OCH(3))](+)+H(+)) by adjusting the pH with Et(3)N (Ldtb(2-) is the deprotonated form of the ligand).On the other hand, potentiometric titration studies of 1 in an ethanol/water mixture (70:30 V/V; I=0.1M KCl) show three titrable protons, indicating the dissociation of the bridging CH(3)O(-) group.The catecholase activity of 1 and 2 in methanol/water buffer (30:1 V/V) demonstrates that the deprotonated form is the active species in the oxidation of 3,5-di-tert-butylcatechol and that the reaction follows Michaelis-Menten behavior with k(cat)=5.33 x 10(-3)s(-1) and K(M)=3.96 x 10(-3)M. Interestingly, 2 can be electrochemically oxidized with E(1/2)=0.27 V vs.Fc(+)/Fc (Fc(+)/Fc is the redox pair ferrocinium/ferrocene), a redox potential which is believed to be related to the formation of a phenoxyl radical.Since these complexes are redox active species, we analyzed their activity toward the nucleic acid DNA, a macromolecule prone to oxidative damage.Interestingly these complexes promoted DNA cleavage following an oxygen dependent pathway. 相似文献
997.
998.
Fernández-López R Garcillán-Barcia MP Revilla C Lázaro M Vielva L de la Cruz F 《FEMS microbiology reviews》2006,30(6):942-966
Plasmids cannot be understood as mere tools for genetic exchange: they are themselves subject to the forces of evolution. Their genomic and phylogenetic features have been less studied in this respect. Focusing on the IncW incompatibility group, which includes the smallest known conjugative plasmids, we attempt to unveil some common trends in plasmid evolution. The functional modules of IncW genetic backbone are described, with emphasis on their architecture and relationships to other plasmid groups. Some plasmid regions exhibit strong phylogenetic mosaicism, in striking contrast to others of unusual synteny conservation. The presence of genes of unknown function that are widely distributed in plasmid genomes is also emphasized, exposing the existence of ill-defined yet conserved plasmid functions. Conjugation is an essential hallmark of IncW plasmid biology and special attention is given to the organization and evolution of its transfer modules. Genetic exchange between plasmids and their hosts is analysed by following the evolution of the type IV secretion system. Adaptation of the trw conjugative machinery to pathogenicity functions in Bartonella is discussed as an example of how plasmids can change their host modus vivendi. Starting from the phage paradigm, our analysis articulates novel concepts that apply to plasmid evolution. 相似文献
999.
Drosophila melanogaster is a key model system that has greatly contributed to the advance of developmental biology through its extensive and sophisticated genetics. Nevertheless, only a few in vitro approaches are available in Drosophila to complement genetic studies in order to better elucidate developmental mechanisms at the cellular and molecular level. Here we present a dissociated cell culture system generated from the optic lobes of Drosophila larval brain. This culture system makes it feasible to study the proliferative properties of Drosophila postembryonic Nbs by allowing BrdU pulse and chase assays, as well as detailed immunocytochemical analysis with molecular markers. These immunofluorescence experiments allowed us to conclude that localization of asymmetric cell division markers such as Inscuteable, Miranda, Prospero and Numb is cell autonomous. By time-lapse video recording we have observed interesting cellular features of postembryonic neurogenesis such us the polarized genesis of the neuroblast progeny, the extremely short ganglion mother cell (GMC) cell cycle, and the last division of a neuroblast lineage. The combination of this cell culture system and genetic tools of Drosophila will provide a powerful experimental model for the analysis of cell cycle and asymmetric cell division of neural progenitor cells. 相似文献
1000.
The processing of stem cell lines for application in human therapy requires a physical environment in which air quality (i.e., the number of airborne particles) is controlled to minimize risk of contamination. The processing facility should be constructed and operated to minimise the introduction, generation and retention of particles and microorganisms. A formal program of environmental monitoring should be maintained in each stem cell bank to specify and assess key factors and their influence on the microbiological quality of the process and product. This program should assure the manipulation of cells involved in the derivation of stem cell lines and their culture under established limits for airborne particles and for microbial contamination of the air and surfaces. Environmental monitoring should also address the regulatory requirements in the countries in which the cells will be used. The monitoring programme will depend on local conditions in each processing centre or cell bank. Each centre will need to evaluate its specific needs and establish appropriate monitoring procedures which should not become intrusive to the extent that they might compromise the quality of the cell banks or products. 相似文献