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1.
Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned “natural” instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a “collapse”. We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor. 相似文献
2.
Chemosensory dendritic membranes (olfactory cilia) contain protein kinase activity that is stimulated by cyclic AMP and more efficiently by the nonhydrolyzable GTP analog guanosine-5'-O-(3-thio)triphosphate (GTP gamma S). In control nonsensory (respiratory) cilia, the cyclic AMP-dependent protein kinase is practically GTP gamma S-insensitive. GTP gamma S activation of the olfactory enzyme appears to be mediated by a stimulatory GTP-binding protein (G-protein) and adenylate cyclase previously shown to be enriched in the sensory membranes. Protein kinase C activity cannot be detected in the chemosensory cilia preparation under the conditions tested. Incubation of olfactory cilia with [gamma-32P]ATP leads to the incorporation of [32P]phosphate into many polypeptides, four of which undergo covalent modification in a cyclic nucleotide-dependent manner. The phosphorylation of one polypeptide, pp24, is strongly and specifically enhanced by cyclic AMP at concentrations lower than 1 microM. This phosphoprotein is not present in respiratory cilia, but is seen also in membranes prepared from olfactory neuroepithelium after cilia removal. Cyclic AMP-dependent protein kinase and phosphoprotein pp24 may be candidate components of the molecular machinery that transduces odor signals. 相似文献
3.
Eliahu Heldman Ayala Balan Ora Horowitz Sarit Ben-Zion Michael Torten 《FEBS letters》1985,180(2):243-248
Antiparaoxon immune sera were employed in a new immunoassay based on competition between acetylcholinesterase and antibodies for the binding ofparaoxon. Unlike radioimmunoassay, the new assay described herein can be extended to predict the feasibility of antibodies to confer in vivo protection of acetylcholinesterase against organophosphate poisoning. The toxicity of paraoxon was reduced in mice which were pre-injected with the immune sera. 相似文献
4.
A brief pulse of red light (R) given to darkgrown seedlings ofArabidopsis thaliana (L.) Heyn. potentiates rapid synthesis of chlorophyll upon transfer to continuous white light. The time course for potentiation
of rapid greening shows that a R pulse in the LF (low fluence) range has maximal effect within a few hours, and that there
is a small VLF (very low fluence) component as well. Partial reversal of the effect of R by far-red light (FR) indicates that
the pulse acts through phytochrome. As it does in the wild-type (WT), a pulse of R accelerates greening of long-hypocotyl
(hy) mutants. The extent of induction by the R pulse was about the same in the WT and in allhy mutants studied. Reversibility by FR was greatly decreased in thehy-1 andhy-2 strains. It is possible that these mutants contain a species of phytochrome with defective phototransformation kinetics.
If there is such a defective phytochrome species, it nevertheless appears to be active in the potentiation of rapid greening.
Dedicated to Professor Hans Mohr on the occasion of his 60th birthday 相似文献
5.
6.
Molecular characterization of salt-stress-associated protein in citrus: protein and cDNA sequence homology to mammalian glutathione peroxidases 总被引:16,自引:0,他引:16
Doron Holland Gozal Ben-Hayyim Zehava Faltin Luc Camoin A. Donny Strosberg Yuval Eshdat 《Plant molecular biology》1993,21(5):923-927
A gene encoding for a citrus salt-stress-associated protein (Cit-SAP) was cloned from Citrus sinensis salt-treated cell suspension. The gene, designated csa, was isolated from a cDNA expression library. The partial amino acid sequence of the protein, as well as that deduced from the nucleotide sequence of csa, revealed a considerable homology to mammalian glutathione peroxidase (GP), and to clone 6P229 from tobacco protoplasts. The increased expression of Cit-SAP in NaCl-treated cultured citrus cells and in citrus plants irrigated with saline water, and its similarity to GP, raise the possibility that one of the effects of salt stress in plants may be the increase of the level of free radicals. 相似文献
7.
In a search for genes that are induced in citrus cell suspension in response to salt stress, a cDNA clone with high homology to cotton Lea5 gene was isolated. Data base analysis of the protein deduced from the nucleotide sequence indicates that, like in cotton, the protein from citrus contains regions with significant hydropathic character. The gene, designated C-Lea5, is expressed in citrus leaves as well as cell suspension. The steady-state level of C-Lea5 is increased in cell suspension that is grown in the presence of 0.2 M NaCl. This phenomenon is also observed in leaves of citrus plants irrigated with NaCl and in citrus seedlings which are exposed to drought and heat stress. We suggest that the osmotic stress resulted from elevated level of salt is responsible for the increase in the level of C-Lea5. 相似文献
8.
Lancet Doron; Kauer John S.; Greer Charles A.; Shepherd Gordon M. 《Chemical senses》1981,6(4):343-349
The olfactory epithelium of the salamander and the mouse hasbeen analyzed for patterns of activity elicited by odor stimulation.A high-resolution adaptation of the 2-deoxyglucose (2DG) methodwas used, involving freeze-substitution in anhydrous acetonecombined with nuclear emulsion autoradiography, according toSejnowski et al. (1980). In animals exposed to the odor of amylacetate, the autoradiograms of 2 µg thick sections showedrestricted regions of high [14C]2DG and [3H]2DG uptake. Withinthese regions, there was a characteristic pattern of diffuselocalization in the superficial supranuclear zone; small clumpsor strands of grains in the receptor cell nuclei layer; andthick clumps of grains in the basal cell layer. The relationof these patterns of differential odorinduced activity in thecells of the epithelium is discussed.
* Present address: Department of Membrane Research, The WeizmannInstitute of Science, Rehovot, Israel 相似文献
9.
Lina Abu-Tair Sarit Doron Mahmud Mahamid Johnny Amer Rifaat Safadi 《Mitochondrion》2013,13(5):473-480
We investigated leptin effects on lymphocyte interactions with hepatic-stellate-cells (HSCs). Leptin showed pro-fibrotic effects on HSCs with oxidative status imbalance.In co-cultures, leptin activates HSCs and consequently adhered HCV-lymphocytes more than healthy ones. Leptin also increased healthy and HCV lymphocyte proliferations; increased their reactive-oxygen-species; decreased antioxidants (reduced-glutathione) levels while inhibited apoptosis only of HCV-lymphocytes. The leptin-treated HCV-lymphocytes activated HSCs, increase interleukin-4 while decreased their apoptosis.Leptin-receptor-deficient (db–db)-HSCs did not adhere lymphocytes. db/db-lymphocytes however showed fewer adherences to HSCs when compared to WT-counterparts.This study presents immune and oxidative modulatory effects of leptin on lymphocytes and their consequent interaction with HSCs. 相似文献
10.
Rob J. Van Geest Ingeborg Klaassen Sarit Y. Lesnik-Oberstein H. Stevie Tan Marco Mura Roel Goldschmeding Cornelis J. F. Van Noorden Reinier O. Schlingemann 《Journal of cell communication and signaling》2013,7(1):1-9
In proliferative diabetic retinopathy (PDR), vascular endothelial growth factor (VEGF) and CCN2 (connective tissue growth factor; CTGF) cause blindness by neovascularization and subsequent fibrosis. This angio-fibrotic switch is associated with a shift in the balance between vitreous levels of CCN2 and VEGF in the eye. Here, we investigated the possible involvement of other important mediators of fibrosis, tissue inhibitor of metalloproteinases (TIMP)-1 and transforming growth factor (TGF)-β2, and of the matrix metalloproteinases (MMP)-2 and MMP-9, in the natural course of PDR. TIMP-1, activated TGF-β2, CCN2 and VEGF levels were measured by ELISA in 78 vitreous samples of patients with PDR (n = 28), diabetic patients without PDR (n = 24), and patients with the diabetes-unrelated retinal conditions macular hole (n = 10) or macular pucker (n = 16), and were related to MMP-2 and MMP-9 activity on zymograms and to clinical data, including degree of intra-ocular neovascularization and fibrosis. TIMP-1, CCN2 and VEGF levels, but not activated TGF-β2 levels, were significantly increased in the vitreous of diabetic patients, with the highest levels in PDR patients. CCN2 and the CCN2/VEGF ratio were the strongest predictors of degree of fibrosis. In diabetic patients with or without PDR, activated TGF-β2 levels correlated with TIMP-1 levels, whereas in PDR patients, TIMP-1 levels, MMP-2 and proMMP-9 were associated with degree of neovascularization, like VEGF levels, but not with fibrosis. We confirm here our previous findings that retinal fibrosis in PDR patients is significantly correlated with vitreous CCN2 levels and the CCN2/VEGF ratio. In contrast, TIMP-1, MMP-2 and MMP-9 appear to have a role in the angiogenic phase rather than in the fibrotic phase of PDR. 相似文献