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51.
Clear water associated with biomass and nutrient variation during the growth of a Charophyte stand after a drawdown,in a tropical coastal lagoon 总被引:1,自引:1,他引:0
The community of Charophytes in the Imboassica coastal lagoon in Brazil (22° 24 S and 42° 42 W) sometimes occupies almost the entire benthic region, and presents a large variation in C:N:P ratio. The effect of drawdown on the regeneration and buildup of biomass and on the nutrient concentration of these macroalgae was studied at three different sampling sites. Drawdown results in a high level of mortality in the macroalgae stands and after the water level later rises, the process of oospore germination begins. The drawdowns occurred in November 96 and January 97, and after March 97 we took samples in order to determine biomass values and the concentration of carbon, nitrogen and phosphorus. The results indicate that the fast growth of Charophytes may absorb a great amount of the nutrients entering the lagoon. The biomass reached maximum values of between 400 and 600 g DW m–2, and the C:N:P ratio varied from 51:7:1 to 1603:87:1, indicating that this macroalgae may grow in a wide range of nutrient concentration. The presence of this community in the Imboassica lagoon may act as one of the limiting factors controlling phytoplanktonic primary production, decreasing nutrient availability in the water column (`bottom-up' control) and keeping the water clear after drawdowns. Probably through the habitat structure produced by the great biomass reached, they provide substrate and shelter for the structuring of a community with grazing zooplankton, which acts as a `top-down' controlling mechanism on the phytoplankton. 相似文献
52.
TNF-TNFR2 interactions promote MHC class II-stimulated alloresponses while TNF-TNFR1 interactions promote MHC class I-stimulated alloresponses. The present studies were designed to evaluate whether TNF-TNFR2 interactions were involved in the in vivo generation of CD4(+) T cell-mediated intestinal graft-versus-host disease (GVHD) in the (C57BL/6J (hereafter called B6) --> B6 x B6.C-H-2(bm12) (bm12))F(1) GVHD model. Briefly, 5 x 10(6) splenic CD4(+) T lymphocytes from B6.TNFR2(-/-) or control B6 mice were transferred with 1--2 x 10(6) T cell-depleted B6 bone marrow cells (BMC) to irradiated MHC class II-disparate (bm12 x B6)F(1) mice. Weight loss, intestinal inflammation, and the surface expression of CD45RB (memory marker) on intestinal and splenic lymphocytes were assessed. IL-2 and IFN-alpha mRNA levels in intestinal lymphocytes were assessed by nuclease protection assays. A significant reduction in weight loss and intestinal inflammation was observed in recipients of the TNFR2(-/-)CD4(+) SpC. Similarly, a significant decrease was noted in T cell numbers and in CD45RB(low) (activated/memory) expression on intestinal but not CD4(+) T cells in recipients of TNFR2(-/-)CD4(+) spleen cells. IL-2 and IFN-alpha mRNA levels were reduced in the intestine in the recipients of TNFR2(-/-) splenic CD4(+) T cells. These results indicate that TNF-TNFR2 interactions are important for the development of intestinal inflammation and activation/differentiation of Th1 cytokine responses by intestinal lymphocytes in MHC class II-disparate GVHD while playing an insignificant role in donor T cell activation in the spleen. 相似文献
53.
54.
The capacity for 1-kestose uptake into the vacuole of fructan storing Jerusalem artichoke tubers was investigated. 1-kestose serves both as building block for fructan initiation and as a fructose donor for chain elongation. Tonoplast vesicles were isolated from actively storing tubers, and their vesicles were capable of transporting sucrose in a manner indicative of a sucrose/H(+) antiport. Under similar conditions, 1-kestose was not taken up by vesicles energized by either a pH jump or in the presence of ATP. When added together at 2 mM, sucrose uptake was not affected by the presence of 1-kestose. The data argues against the possible synthesis of 1-kestose in the cytosol and subsequent transport to the vacuole. The data also presents definite evidence for the existence a mechanism for sucrose accumulation in fructan storing vacuoles. 相似文献
55.
Time averaged field measurements produced by a Positron dosimeter worn by study subjects was the primary method of exposure evaluation in two Canadian studies of childhood leukemia and AC magnetic field exposure. Statistically significant but mutually contradictory results obtained in the two studies, done in different locales but under similar study conditions, have not been explained. This report examines operational features of the Positron meter, including an unanticipated sensitivity to wearer motion. If the convalescent cases studied were less active than their healthy controls, as one might expect, then the meter's characteristic responses to motion, particularly as they would affect case-control distributions above and below the different referent group cutpoints used in the two studies, could help to explain both the unexpected inverse risks reported in the larger study and the unusually high risks reported in the smaller study. 相似文献
56.
The incorporation of [1-13C] labelled glucose into hodgsonox, a sesquiterpene epoxide with a unique, doubly allylic ether functionality has been studied in axenic cultures of the liverwort Lepidolaena hodgsoniae. Quantitative 13C NMR spectroscopic analysis showed that the isoprene units are derived exclusively from the methylerythritol phosphate pathway. 相似文献
57.
Donor-site morbidity after free vascularized autogenous fibular transfer: subjective and quantitative analyses 总被引:8,自引:0,他引:8
Bodde EW de Visser E Duysens JE Hartman EH 《Plastic and reconstructive surgery》2003,111(7):2237-2242
The purpose of this study was to determine the subjective and quantitative donor-site morbidity after removal of a free vascularized fibula flap for autoreconstruction. Ten patients and six age-matched, healthy control subjects were included in this study. The postoperative periods ranged from 6 to 87 months. Subjective donor-site morbidity was assessed with a patient questionnaire and the Enneking system. For quantification of donor-site morbidity, gait was evaluated during normal walking, walking under visual and cognitive constraints, and walking at a velocity higher than the preferred one. In general, the patient perception of donor-site morbidity was low. Complaints were frequently mentioned, however, including pain (60 percent), dysesthesia (50 percent), a feeling of ankle instability (30 percent), and inability to run (20 percent). Gait analyses revealed that patients walked at a lower preferred velocity, compared with control subjects. Furthermore, they demonstrated significant increases in the coefficients of variation of stride time during walking under visual and cognitive loads and during walking at a velocity higher than the preferred one, compared with normal walking. These increases were not observed for control subjects. These findings suggest that the reautomatization of gait is affected among patients. This study demonstrates that fibula harvesting is associated with low subjective morbidity but frequent complaints. Walking during complex tasks and at high velocities reveals that restoration of gait is not complete after partial fibulectomy. 相似文献
58.
Proske U Gregory E 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2003,136(4):821-825
In the platypus, electroreceptors are located in rostro-caudal rows in skin of the bill, while mechanoreceptors are uniformly distributed across the bill. The electrosensory area of the cerebral cortex is contained within the tactile somatosensory area, and some cortical cells receive input from both electroreceptors and mechanoreceptors, suggesting a close association between the tactile and electric senses. Platypus can determine the direction of an electric source, perhaps by comparing differences in signal strength across the sheet of electroreceptors as the animal characteristically moves its head from side to side while hunting. The cortical convergence of electrosensory and tactile inputs suggests a mechanism for determining the distance of prey items which, when they move, emit both electrical signals and mechanical pressure pulses. Distance could be computed from the difference in time of arrival of the two signals. Much of the platypus' feeding is done by digging in the bottom of streams with the bill. Perhaps the electroreceptors could also be used to distinguish animate and inanimate objects in this situation where the mechanoreceptors would be continuously stimulated. Much of this is speculation, and there is still much to be learned about electroreception in the platypus and its fellow monotreme, the echidna. 相似文献
59.
Formation and nuclear export of tRNA, rRNA and mRNA is regulated by the ubiquitin ligase Rsp5p 总被引:3,自引:0,他引:3
Neumann S Petfalski E Brügger B Grosshans H Wieland F Tollervey D Hurt E 《EMBO reports》2003,4(12):1156-1162
60.
Citrus juice cells accumulate high levels of citric acid in their vacuoles when compared to other organic ions including malate. Uptake of citrate into tonoplast vesicles from Citrus juice cells was investigated in the presence of malate, and after incubation with antibodies raised against the vacuolar malate-specific channel of Kalancho? diagremontiana leaves. Antibodies against the vacuolar malate channel immunoreacted with a protein of similar size in tonoplast extracts from three Citrus varieties differing in citric acid content. Malate channel antibodies inhibited both delta MicroH(+)-dependent and delta MicroH(+)-independent ATP-dependent citrate transport, indicating common domains in both transport systems and to the malate-specific channel of Kalancho? diagremontiana leaves. Malate strongly inhibited electrogenic citrate transport, whereas ATP-dependent citrate uptake was less affected. Kinetic analysis of citrate transport in the presence of malate confirmed the existence of two citrate transport mechanisms and indicated that both citrate and malate share a common transport channel across the tonoplast of Citrus juice cells. 相似文献