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151.
M. Dauwalder S. J. Roux 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(12):67-70
Immunofluorescence techniques have been used to study the distribution of calmodulin in several tissues in etiolated corn (
, var. Bear Hybrid) seedlings. Uniform staining was seen in the background cytoplasm of most cell types. Cell walls and vacuoles were not stained. In coleoptile mesophyll cells the nucleoplasm of most nuclei was stained as was the stroma of most amyloplasts. The lumen border of mature tracheary elements in coleoptiles also stained. In the rootcap the most intensely stained regions were the cytoplasms of columella cells and of the outermost cells enmeshed in the layer of secreted slime. Nuclei in the rootcap cells did not stain distinctly, but those in all cell types of the root meristem did. Also in the root meristem, the cytoplasm of metaxylem elements stained brightly. These results are compared and contrasted with previous data on the localization of calmodulin in pea root apices and epicotyls and discussed in relation to current hypotheses on mechanisms of gravitropism. 相似文献
152.
J-P de Vera G Horneck P Rettberg S Ott 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1236-1243
Complementary to the already well-studied microorganisms, lichens, symbiotic organisms of the mycobiont (fungi) and the photobiont (algae), were used as "model systems" in which to examine the ecological potential to resist to extreme environments of outer space. Ascospores (sexual propagules of the mycobiont) of the lichens Fulgensia bracteata, Xanthoria elegans and Xanthoria parietina were exposed to selected space-simulating conditions (up to 16 h of space vacuum at 10(-3) Pa and UV radiation at 160 nm < or = lambda < or = 400 nm), while embedded in the lichen fruiting bodies. After exposure, the ascospores were discharged and their viability was tested as germination capacity on different culture media including those containing Mars regolith simulant. It was found that (i) the germination rate on media containing Mars regolith simulant was as high as on other mineral-containing media, (ii) if enclosed in the ascocarps, the ascospores survived the vacuum exposure, the UV-irradiation as well as the combined treatment of vacuum and UV to a high degree. In general, 50 % or more viable spores were recovered, with ascospores of X. elegans showing the highest survival. It is suggested that ascospores inside the ascocarps are well protected by the anatomical structure, the gelatinous layer and the pigments (parietin and carotene) against the space parameters tested. 相似文献
153.
P.L Pritchett 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1807-1816
Recent developments regarding collisionless reconnection in current sheets with a finite normal magnetic field component (Bz) are reviewed. In 2-D x, z configurations the ion tearing mode is stabilized by the electron compressibility. When the y dependence is included, cross-field current instabilities can be excited. Of these, the drift kink mode appears to be particularly important. 3-D electromagnetic particle simulations indicate that this mode can act as the precursor to the growth of tearing modes and subsequent reconnection. 相似文献
154.
D O Klymchuk E L Kordyum T V Vorobyova D K Chapman C S Brown 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(10):2283-2288
Changes in the vacuolation in root apex cells of soybean (Glycine max L. [Merr.]) seedlings grown in microgravity were investigated. Spaceflight and ground control seedlings were grown in the absence or presence of KMnO4 (to remove ethylene) for 6 days. After landing, in order to study of cell ultrastructure and subcellular free calcium ion distribution, seedling root apices were fixed in 2.5% (w/v) glutaraldehyde in 0.1 M cacodylate buffer and 2% (w/v) glutaraldehyde, 2.5% (w/v) formaldehyde, 2% (w/v) potassium antimonate K[Sb(OH)6] in 0.1 M K2HPO4 buffer with an osmolarity (calculated theoretically) of 0.45 and 1.26 osmol. The concentrations of ethylene in all spaceflight canisters were significantly higher than in the ground control canisters. Seedling growth was reduced in the spaceflight-exposed plants. Additionally, the spaceflight-exposed plants exhibited progressive vacuolation in the root apex cells, particularly in the columella cells, to a greater degree than the ground controls. Plasmolysis was observed in columella cells of spaceflight roots fixed in solutions with relatively high osmolarity (1.26 osmol). The appearance of plasmolysis permitted the evaluation of the water status of cells. The water potential of the spaceflight cells was higher than the surrounding fixative solution. A decrease in osmotic potential and/or an increase in turgor potential may have induced increases in cell water potential. However, the plasmolysed (i.e. non-turgid) cells implied that increases in water potential were accompanied with a decrease in osmotic potential. In such cells changes in vacuolation may have been involved to maintain turgor pressure or may have been a result of intensification of other vacuolar functions like digestion and storage. 相似文献
155.
Nussinov MD Burdyuzha VV Gleizer SI 《Journal of the British Interplanetary Society》1992,45(6):251-255
An analysis of the experimental data available and of the present theoretical concepts shows that even the initial physicochemical chemical precellular stages of biological evolution are impossible in the interstellar medium, while biomonomers possibly formed on asteroids and comets might have participated after transportation to the Earth in the final stages of the origin of the first precellular biological structures and then in the first living cells. 相似文献
156.
157.
Nussinov MD Lysenko SV Kozlovskii MYu Pogodin YuS 《Journal of the British Interplanetary Society》1992,45(1):13-14
The use of charge-coupled devices is suggested as a means for detecting growth of micro-organism colonies. The accuracy of the method is determined by channel width and the sensitivity by the signal/noise ratio. The method was tested on a dense nutrient medium, which is to be considered more suitable to micro-organisms of the dry Martian soil than the water solution of nutrients employed in the Viking's strategy. 相似文献
158.
L. J. Lanzerotti K. Rinnert G. Dehmel F. O. Gliem E. P. Krider M. A. Uman G. Umlauft J. Bach 《Space Science Reviews》1992,60(1-4):91-109
The Lightning and Radio Emission Detector (LRD) instrument will be carried by the Galileo Probe into Jupiter's atmosphere. The LRD will verify the existence of lightning in the atmosphere and will determine the details of many of its basic characteristics. The instrument, operated in its magnetospheric mode at distances of about 5, 4, 3, and 2 planetary radii from Jupiter's center, will also measure the radio frequency (RF) noise spectrum in Jupiter's magnetosphere. The LRD instrument is composed of a ferritecore radio frequency antenna ( 100 Hz to 100 kHz) and two photodiodes mounted behind individual fisheye lenses. The output of the RF antenna is analyzed both separately and in coincidence with the optical signals from the photodiodes. The RF antenna provides data both in the frequency domain (with three narrow-band channels, primarily for deducing the physical properties of distant lightning) and in the time domain with a priority scheme (primarily for determining from individual RF waveforms the physical properties of closeby-lightning). 相似文献
159.
We show, using the HST — GHRS data on velocity and temperature in the nearby interstellar medium, that the observed 3 – 4 km s–1 relative velocity between the Local Interstellar Cloud (LIC) and the so-called G-cloud located in the Galactic Center hemisphere can be quite naturally explained assuming that the two clouds do interact with each other. In the proposed interpretation the two media are separated by a (quasiperpendicular) MHD shock front propagating from the LIC into the G-cloud. The LIC plasma is then nothing else but the shocked (compression 1.3 – 1.4) gas of the G-cloud. A 1-D single-fluid solution of the Rankine — Hugoniot equations can fit the most probable observed values of the relative velocity (3.75 km/s), LIC (6700 K) and G-cloud (5400 K) kinetic temperatures, if the plasma-beta of the LIC plasma is in the range 1.3 – 1.5 (Table 1). This corresponds to a super — fast magnetosonic motion of the heliosphere through the LIC, independently of LIC density. The LIC magnetic field strength is 1.9 (3.1) G for the LIC electron density ne = 0.04 (0.10) cm–3. In this case the shock is less than 30 000 AU away and moves at about 10 km s–1 relative to the LIC plasma. The Sun is chasing the shock and should catch up with it in about 104 years. If the heliospheric VLP emissions cutoff at 1.8 kHz is indicative of ne (LIC) = 0.04 cm–3 (Gurnett et al., 1993), the (pure plasma) bowshock ahead of the heliopause could be the source of quasi-continuous heliospheric 2-kHz emission band. We believe that with the expected increase in the performance of modern spectroscopic instrumentation the proposed method of magnetic field evaluation may in the future find wider application in the studies of the interstellar medium. 相似文献
160.
P A Craven M J Rycroft 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):45-49
Beyond the magnetic influence of the Earth, the flux of galactic cosmic radiation (GCR) represents a radiological concern for long-term manned space missions. Current concepts of radiation quality and equivalent dose are inadequate for accurately specifying the relative biological "efficiency" of low doses of such heavily ionising radiations, based as they are on the single parameter of Linear Energy Transfer (LET). Such methods take no account of the mechanisms, nor of the highly inhomogeneous spatial structure, of energy deposition in radiation tracks. DNA damage in the cell nucleus, which ultimately leads to the death or transformation of the cell, is usually initiated by electrons liberated from surrounding molecules by the incident projectile ion. The characteristics of these emitted "delta-rays", dependent primarily upon the charge and velocity of the ion, are considered in relation to an idealised representation of the cellular environment. Theoretically calculated delta-ray energy spectra are multiplied by a series of weighting algorithms designed to represent the potential for DNA insult in this environment, both in terms of the quantity and quality of damage. By evaluating the resulting curves, and taking into account the energy spectra of heavy ions in space, a relative measure of the biological relevance of the most abundant GCR species is obtained, behind several shielding configurations. It is hoped that this method of assessing the radiation quality of galactic cosmic rays will be of value when considering the safety of long-term manned space missions. 相似文献