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921.
S.K. Das M. Masuda M. Hatashita A. Sakurai M. Sakakibara 《Letters in applied microbiology》2008,47(6):534-538
Aims: To obtain a higher cordycepin production using Cordyceps militaris mutant obtained by a new mutagenesis technique called ‘ion beam’. Methods and Results: Successful irradiation of C. militaris NBRC 9787 by a proton beam with high energy was performed, and 30 classes of 8‐azaadenine‐ and 28 classes of 8‐azaaguanine‐resistant mutants were obtained on mutant screening, of which seven classes were selected as promising preliminary mutants having an antibacterial ability as an index of cordycepin production. In a surface liquid culture technique, some of the 8‐azaadenine‐resistant mutants gave a better performance for the cordycepin productivity; in contrast, among the 8‐azaaguanine‐resistant mutants, it was shown that mutant no. G81‐3 was much better than the control in the metabolic rate of glucose and the cordycepin productivity. In primary optimization using the enriched medium, the cordycepin production was 3·1 and 1·8 g l?1 on 21‐day culture for mutant no. G81‐3 and the control, respectively. The cordycepin production obtained by the mutant was 72% more than the control. Conclusions: The mutant obtained by proton beam irradiation had higher productivity of cordycepin than that of the control. Significance and Impact of the Study: The mutant obtained by irradiation had a superior production performance of cordycepin, and therefore, it could be used in the realm of applied industrial biotechnology for the large‐scale production of cordycepin. 相似文献
922.
Aim To evaluate the relative effectiveness of the lower and upper sections, respectively, of the Amazon River as a barrier to bird distribution, and to evaluate ecological and taxonomic factors affecting the efficacy of the river barrier. Location Amazon River of South America between its confluence with the Napo River in the west and its delta in the east. Methods Using published distribution maps for 448 species of passerine birds occurring along the Amazon River, we evaluated whether each was distributed along one bank only (river presumed to be a barrier) or both banks (no barrier) to test the predictions that the river was more effective as a dispersal barrier: (1) along the lower, wider portion of the river than the upper, narrower portion; (2) for species inhabiting forests than open country; (3) for species inhabiting forest understorey than forest canopy; (4) for species restricted to terra firme (never inundated upland forest) than those not restricted to terra firme and (5) for certain taxonomic groups. Results Our analyses demonstrated that the Amazon River was most effective as a dispersal barrier along its lower portion and for species restricted to forests and terra firme. However, the river was not significantly more of a barrier for species inhabiting forest understorey than forest canopy. The river was most significant as a barrier to dispersal for the antbirds (Thamnophilidae) and was less significant as a barrier to species belonging to several large families including woodcreepers (Dendrocolaptidae), ovenbirds (Furnariidae), flycatchers (Tyrannidae), cotingids (Cotingidae), tanagers (Thraupidae), seed‐eating finches (Emberizidae) and blackbirds (Icteridae). Main conclusions The robust widths of Amazonian rivers are widely considered to represent impediments to dispersal and gene flow for many taxa of birds and other animals, and may have represented agents of vicariance in the diversification of species. Our study reaffirms the effectiveness of the lower Amazon River as a current barrier to bird dispersal for forest birds and provides new insights into the effects of habitat and taxonomy on the efficacy of the river barrier. Although supportive of several predictions of the river hypothesis of biological diversification, our study is limited in addressing the historical impact of river barriers as agents of vicariance in the process of diversification. 相似文献
923.
924.
Using a patch-clamp technique, we studied the biophysical properties of large-conductance channels in the nuclear envelope
of rat cerebellar Purkinje neurons. Our experiments showed that channels with identical conductance, selectivity, and kinetics
are expressed in the external and internal nuclear membranes of these cells. These channels connect the perinuclear space
with the cyto-and nucleoplasm; they are not channels of the complex of the nuclear pores for passive diffusion of ions and
small molecules, as was believed earlier [17]. We hypothesize that large-conductance cationic channels in the membranes of
the nuclear envelope are identical to ion channels of the endoplasmic reticulum and are necessary for functioning of the intermembrane
space of the envelope as a calcium store.
Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 113–118, March–April, 2007. 相似文献
925.
Huxel GR 《Bulletin of mathematical biology》2007,69(6):2093-2104
The structure and dynamics of food webs are largely dependent upon interactions among consumers and their resources. However,
interspecific interactions such as intraguild predation and interference competition can also play a significant role in the
stability of communities. The role of antagonistic/synergistic interactions among predators has been largely ignored in food
web theory. These mechanisms influence predation rates, which is one of the key factors regulating food web structure and
dynamics, thus ignoring them can potentially limit understanding of food webs. Using nonlinear models, it is shown that critical
aspects of multiple predator food web dynamics are antagonistic/synergistic interactions among predators. The influence of
antagonistic/synergistic interactions on coexistence of predators depended largely upon the parameter set used and the degree
of feeding niche differentiation. In all cases when there was no effect of antagonism or synergism (a
ij
=1.00), the predators coexisted. Using the stable parameter set, coexistence occurred across the range of antagonism/synergism
used. However, using the chaotic parameter strong antagonism resulted in the extinction of one or both species, while strong
synergism tended to coexistence. Whereas using the limit cycle parameter set, coexistence was strongly dependent on the degree
of feeding niche overlap. Additionally increasing the degree of feeding specialization of the predators on the two prey species
increased the amount of parameter space in which coexistence of the two predators occurred. Bifurcation analyses supported
the general pattern of increased stability when the predator interaction was synergistic and decreased stability when it was
antagonistic. Thus, synergistic interactions should be more common than antagonistic interactions in ecological systems. 相似文献
926.
Ghanshyam S. Chauhan Kalpana Chauhan Sandeep Chauhan Sunil Kumar Anita Kumari 《Carbohydrate polymers》2007,70(4):415-421
Pine needles and their carboxymethyl forms were functionalized by network formation with 2-acrylamido-2-methylpropanesulphonic acid (AAmPSA) in the presence of N,N-methylene bisacrylamide. N-Tetramethylethylene diamine and ammonium persulfate were used as accelerator-initiator systems to prepare these hydrogels. The hydrogels were characterized by FTIR, SEM, and nitrogen analysis and for water uptake capacities before and after metal ion sorption with a view to evaluating their use in the removal of toxic ionic species from waste water. A detailed study of Cr6+ adsorption was carried out as a function of time, temperature, pH, and ionic strength. The thermodynamic parameters of adsorption such as ΔH0, ΔS0, and ΔG0 have been evaluated to understand the underlying mechanism of adsorption. In order to understand their reusability in possible technological applications, biodegradability of these hydrogels and their precursors was studied. 相似文献
927.
Inhibitory effects of gold(III) ions (Au(III)) on ribonuclease A (RNase A) and deoxyribonuclease I (DNase I) were investigated at neutral pH. RNase A was completely inhibited by 3 molar equivalents of Au(III) ions. DNase I was inhibited by 10 molar equivalents of Au(III) ions. Stoichiometric analyses suggest that Au(III) ions were coordinated to RNase A molecules. The Au(III)-inhibited RNase A and DNase I were renatured to exhibit 80% and 60% of their intrinsic activity, when the bound Au(III) ions were eliminated from the nucleases by addition of thiourea, which forms a strong complex with gold ions. This suggests that RNase A and DNase I were not oxidized to lose their activity, but reversibly complexed with Au(III) ions to lose their activity. Au(III) ions were probably considered to be bound to histidine and methionine residues in the nucleases, resulting in the inhibition of their activity. CD spectra revealed that the Au(III)-induced inhibition caused a conformational change in RNase A molecules and that the addition of thiourea induced refolding of the Au(III)-inhibited RNase A. 相似文献
928.
929.
930.
Zinc in plants 总被引:15,自引:0,他引:15
Zinc (Zn) is an essential component of thousands of proteins in plants, although it is toxic in excess. In this review, the dominant fluxes of Zn in the soil-root-shoot continuum are described, including Zn inputs to soils, the plant availability of soluble Zn(2+) at the root surface, and plant uptake and accumulation of Zn. Knowledge of these fluxes can inform agronomic and genetic strategies to address the widespread problem of Zn-limited crop growth. Substantial within-species genetic variation in Zn composition is being used to alleviate human dietary Zn deficiencies through biofortification. Intriguingly, a meta-analysis of data from an extensive literature survey indicates that a small proportion of the genetic variation in shoot Zn concentration can be attributed to evolutionary processes whose effects manifest above the family level. Remarkable insights into the evolutionary potential of plants to respond to elevated soil Zn have recently been made through detailed anatomical, physiological, chemical, genetic and molecular characterizations of the brassicaceous Zn hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri. 相似文献