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71.
超低能重离子注入作物育种的原初物理机制 总被引:2,自引:0,他引:2
从原子核物理学观点出发,采用理论分析与实验测量并举的方法对超级能(〈200kev)重离子(Z≥6)注入作物(小麦)种子进行诱变育种的原初物理机制进行了研究,结果表明,无论是注入离子本身的射程,还是次级电子,自由基扩散,高温热穗,级联原子和冲击波等次级作用范围都无法触及表皮下面的胚细胞,但注入离子在麦胚内主要元素(C,N,O,S,P,K,Ca)上激发出的特征X-射线,在其强度减弱为原来的10^-3时 相似文献
72.
Effects of heavy metals on pollen tube growth and ultrastructure 总被引:3,自引:0,他引:3
Summary The influence of different concentrations of the heavy metals cadmium (Cd2+), cobalt (Co2+), copper (Cu2+), iron (Fe2+ and Fe3+), mercury (Hg2+), manganese (Mn2+), and zinc (Zn2+), plus aluminium (Al3+) (a toxic metal in polluted areas), on pollen germination and tube growth ofLilium longiflorum was investigated using light microscopy. Effects could be observed with 3 M and 100 M of heavy metal, added as chloride salts to the medium. Cd2+, Cu2+, and Hg2+, showed the greatest toxicity, whereas germination and growth rate was less affected by Mn2+. Affected tubes showed swelling of the tip region. Tubes treated with Cd2+, Co2+, Fe2+, Fe3+, Hg2+, and Mn2+ were also prepared for ultrastructural studies. In all cases, the main effect was abnormal cell wall organization, mostly at the tip, where round, fibrillar aggregates, the shape and size of secretory Golgi vesicles were formed. They built up a loose network which could be up to 10 m thick compared to untreated tubes where the cell wall was composed of thin layers of long fibrils and about 100 nm thick. Cd2+ was the only metal which produced effects at the intracellular level: organelle distribution within the tip region appeared disorganized. A general mechanism of heavy metal action on pollen tube growth is discussed. 相似文献
73.
Acid atmospheric deposition can cause losses of metal nutrients from the organic layer of a soil. The size of these losses
depend on the sizes of the different pools in which the metals are present, as these pools differ in mobility. The metal pools
in an organic soil layer of a Douglas fir forest in the Netherlands subjected to acid deposition were determined by means
of extractions and percolations. Na was mainly dissolved and exchangeably adsorbed, K dissolved, exchangeably adsorbed and
present in the soil microbial biomass, Ca exchangeably adsorbed and present in organic precipitates, Mg exchangeably adsorbed
and present in the soil biomass, and Mn exchangeably adsorbed and present in inorganic precipitates. The main part of the
metals was exchangeably adsorbed. The adsorption affinity increased in the order Na < K < Mg < Mn ≈ Ca. The vertical distribution
of the metals in the organic layer showed that all metals were continuously lost from the organic layer. The differences between
the metals in retention and vertical distribution patterns were in agreement with their differences in deposition rate, pool
distribution, and exchange affinity. Since the metals were mainly exchangeably adsorbed, and the acidifying cations dominated
the atmospheric deposition, acid deposition and cation exchange must be processes that strongly affect the losses of metals
from this organic soil layer. R F Huettl Section editor 相似文献
74.
Mittal Chandra K. Harrell William B. Mehta Chander S. 《Molecular and cellular biochemistry》1995,149(1):263-265
This study was designed to evaluate thein vitro effects of transition heavy metal cations on activity of constitutive isoform of nitric oxide synthase (cNOS) in rat brain. NOS activity was determined in the cytosolic fractions of rat cerebral hemispheres by conversion of3H-L-arginine to3H-L-citrulline. Different concentrations of mercury (Hg2+), nickel (Ni2+), manganese (Mn2+), zinc (Zn2+), cadmium (Cd2+), lead (Pb2+) and calcium (Ca2+) were tested on NOS activity. While all the cations caused inhibition, there were differences in the apparent inhibition constants (Ki) among the cations. With the exception of calcium ion no other cation required preincubation with the enzyme preparation. These results indicate that while calcium ion modulate cNOS activity at regulatory site(s), inhibitory influence of toxic heavy metal cations may be exerted on the catalytic site(s) either by direct binding to it or by interfering with the electron transfer during catalysis. 相似文献
75.
Toxicology of vanadium compounds in diabetic rats: The action of chelating agents on vanadium accumulation 总被引:1,自引:0,他引:1
Jose L. Domingo Mercedes Gomez Domenec J. Sanchez Juan M. Llobet Carl L. Keen 《Molecular and cellular biochemistry》1995,153(1-2):233-240
The possible use of vanadium compounds in the treatment of diabetic patients is now being evaluated. However, previously to establish the optimal maximum dose for diabetes therapy, it should be taken into account that vanadium is a highly toxic element to man and animals. The toxic effects of vanadium are here reviewed. The tissue vanadium accumulation, which would mean an additional risk of toxicity following prolonged vanadium administration is also discussed. Recently, it has been shown that coadministration of vanadate and TIRON, an effective chelator in the treatment of vanadium intoxication, reduced the tissue accumulation of this element, decreasing the possibility of toxic side effects derived from chronic vanadium administration without diminishing the hypoglycemic effect of vanadium. However, previously to assess the effectiveness of this treatment in diabetic patients, a critical reevaluation of the antidiabetic action of vanadium and its potential toxicity is clearly needed. 相似文献
76.
The effects of inorganic mercury (HgII) and methylmercury (MeHg) on the colonization of artificial substrates by periphytic
diatoms were studied using indoor freshwater microcosms. These consisted of a mixed biotope– water column + natural sediment
– with rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea).The periphyton was collected
on glass slides in the water column after 34and 71 days. The two Hg sources were introduced either by daily additions to the
water column, or once at the beginning into the sediment, using two nominal concentrations: water column, 0.5 μgL-1 and 2 μg L-1 for both compounds: sediment, 0.5 mg kg-1 (fw) and 2 mgkg-1 (fw) for MeHg and 1 mg kg-1 (fw) and 10 mgkg-1 (fw) for HgII. Several complementary criteria were used to analyse the structural and functional perturbations induced: cell
density, species richness, diatom size, relative abundance. Exposure to MeHg added to the water column resulted in reduced
cell density and changes in species composition with enhancement of e.g. Fallacia pygmaea or Nitzschia palea; inorganic Hg
had less effect on the population structure. After contamination via the sediment, the effects of the two compounds were less
pronounced than for the water source.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
77.
Effects of cadmium,copper, and zinc on growth and thiol content of aquatic hyphomycetes 总被引:3,自引:1,他引:2
The effects of cadmium, copper, and zinc on the growth of ten strains ofaquatic hyphomycetes were investigated. On a solid medium, Cd and Cu reducedradial growth of most strains by 50% at concentrations between150–400 µM; in a liquid medium, the strains were more sensitive.The inhibitory effects of zinc were much less severe. Two isolates(Articulospora tetracladia and Tetracladium marchalianum) from a copper-minestream were more resistant against copper than conspecific strains from anon-polluted stream. Heliscus lugdunensis and Varicosporium elodeaeresponded to Cd exposure, but not to Cu or Zn exposure, by increasedsynthesis of SH-containing compounds. Glutathione levels showed a unimodalresponse to increasing Cd and Zn exposure. With copper, glutathionedecreased at intermediate levels of contamination. In the presence of Cd, H. lugdunensis synthesized several unknown sulfur-rich substances that wereabsent or produced at reduced rates in control cultures. 相似文献
78.
Offshore fluxes of Cu, Zn, Cd, Pb and Hg were calculated based onresidual flow patterns and salinity gradients along the Belgian
coast. Theresidual flow lines along the Belgian coast are more or less parallel to thecoast except in the area where the north-easterly
flowing watermass comingfrom the Channel encounters the south-westerly-oriented Scheldt outflow,forming a residual hydrodynamical
front. From the steady-state salinitypattern, diffusion coefficients perpendicular to the residual flow werededuced; they
ranged from 21 to 108 m2 s-1.
Offshore fluxes of dissolved and particulate trace metals based on diffusiveand mixing processes are calculated. The steady
state profiles of dissolvedmetals show a dilution effect in the coastal waters, reaching an almostconstant concentration in
the marine watermass in the 1981–1983dataset. The ratios of the Scheldt input of trace metals to the totaldissolved offshore
flux vary from 38 to 55% (1981–1983),depending on the kind of metal, and from 55 to 91% (1995–1996).The ratio of the Scheldt
input to the dissolved metal flow parallel to thecoast, is in both periods (1981–1983 and 1995–1996), smallerthan 1%. The
steady-state concentration profiles of particular metalsversus salinity are fairly constant in the coastal-estuarine and marinewatermasses,
but decrease very abruptly from the first to the secondwatermass. Assuming a conservative behaviour of the particular metals,offshore
fluxes and the resulting concentration increases agree fairly wellwith the observed values. The ratios of the Scheldt input
to the particulatetrace metal offshore flux vary between 30 to 46% (1981–1983)and 13 to 37% (1995–1996). The contribution
of the Scheldtestuary to the flows parallel to the coast ranges from 1.6 to 2.9%(1981–1983) and from 0.6 to 1.6% (1995).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
79.
The Sea of Marmara, an intercontinental basin with shallow and narrowstraits, connects the Black and Mediterranean Seas. Data
obtained during1991–1996 have permitted the determination of the elementalcomposition of seston in the euphotic zone and the
N:P ratio of thesubhalocline waters of the Marmara Sea. Since primary production is alwayslimited to the less saline upper
layer (15–20 m), of the Marmara Sea,the subhalocline waters of Mediteranean origin are always rich in nutrients(NO3 + NO2 = 8–10 μm, PO4 = 0.8–1.2 μm) but depleted in dissolvedoxygen (30–50 μm) throughout the basin, yielding an -O_2 : N : P ratio of 178 : 9 : 1. Pollution of the surfacewaters since the 60s has modified the subhalocline nutrient chemistryslightly.
In the euphotic zone, the N : P ratio of the seston changes from5.9 to 9.5 between the less and more productive periods. Though
the biologyof the Marmara has changed significantly during the previous two decades,the close relationship observed between
the elemental composition of thesurface seston and the NO3 : PO4 ratio of thesubhalocline waters strongly suggests that during the whole year primaryproduction throughout the basin and POM
export to the lower layer remainnitrogen-limited. This suggestion needs to be confirmed by bio-assays,biological studies and
sediment trap data from the upper subhaloclinedepths. Nonetheless, the counterflows in the Marmara basin possessrelatively
low N : P ratios in both dissolved and particulate nutrients andextend as far as the adjacent seas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.
The mangroves of Kerala on the south-west coast of India are fast disappearing due to land reclamation and other anthropogenic
disturbances. There are very few ecosystem level studies made in these much threatened biotopes in Kerala. The present study
involves the measurement of heavy metals in the mangrove flora and sediments of three mangrove habitats along the Kerala coast.
Sampling was carried out for a period of one year at bi-monthly intervals, with concentrations of Fe, Mn, Cu,Zn,Pb and Co
analysed using atomic absorption spectrophotometry. An appreciable variation was observed in metal concentrations indifferent
mangrove species. Cu, Zn and Pb were found to be in higher concentrations in Avicennia officinalis whereas higher levels of
Fe, Mn and Co were observed in the species Barringtonia racemosa. The analysis of heavy metals indicated a high level of metal
pollutants such as Fe, Cu, Zn and Pb in the mangrove habitats of Quilon and Veli compared to the relatively uncontaminated
areas of Kumarakom.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献