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31.
Particulate organic matter in a mountain stream in the south-western Cape,South Africa 总被引:2,自引:2,他引:0
The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a second-order, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m–2y–1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ m–2y–1). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g m–2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g m–2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46–64% of BOM standing stock, ultra-fine BOM (UBOM) 16–33% and leaf packs 13–24%. The mean annual calorific value of total BOM standing stock was 1709 KJ m–2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size (CBOM 27–100; FBOM 25–27; UBOM 13–19) with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates. 相似文献
32.
In highly eutrophic ponds, buoyancy of the gas-vacuolate blue-green alga Anabaenopsis Elenkinii (Miller) was regulated by complex interactions between chemical and physical parameters, as well as by biological interactions
between various trophic levels. Algal buoyancy and surface bloom formation were enhanced markedly by decreased light intensity,
and to a lesser extent by decreased CO2 availability and increased availability of inorganic nitrogen. In the absence of dense populations of large-bodied Cladocera,
early season blooms of diatoms and green algae reduced light availability in the ponds thus creating conditions favorable
for increased buoyancy and bloom formation by A. Elenkinii. The appearance of blue-green algal blooms could be prevented by a reduced density of planktivorous fish, which allowed development
of dense cladoceran populations. The cladocerans limited the growth of precursory blooms of diatoms and green algae, and given
the resulting clear-water conditions, buoyancy of A. Elenkinii was reduced, and blue-green algal blooms never appeared. 相似文献
33.
Role of the hinge protein in the electron transfer between cardiac cytochrome c1 and c. Equilibrium constants and kinetic probes 总被引:1,自引:0,他引:1
A role of the hinge protein is studied in the electron transfer reaction between cytochromes c1 and c, using highly purified "one-band" cytochrome c1 and "two-band" cytochrome c1. The results show that the hinge protein (Hp), which is essential for a stable ionic strength-sensitive c1-Hp-c complex, seems to play a certain role in electron transfer between cytochromes c1 and c; Keq for electron transfer reaction between cytochromes c1 and c in the presence of the hinge protein is found to be about 40% higher than that in the absence of the hinge protein at low ionic strength, but no difference exists at high ionic strength. We propose a hypothesis that the hinge protein may function as regulator for the electron transfer reaction between cytochromes c1 and c, and this may be at least one of the roles of the hinge protein in mitochondria. 相似文献
34.
The cellular and network effects of acetylcholine (ACh) on the control system for feeding in Limax maximus were measured by intracellular recordings from feeding command-like interneurons and whole nerve recordings from buccal ganglion motor nerve roots that normally innervate the ingestive feeding muscles. The buccal ganglion motor nerve root discharge pattern that causes rhythmic feeding movements, termed the feeding motor program (FMP), was elicited either by attractive taste solutions applied to the lip chemoreceptors or by ACh applied to the cerebral ganglia. The ability of exogenous ACh applied to the cerebral ganglia to trigger FMP was blocked by the cholinergic antagonists curare and atropine. If the strength of the lip-applied taste stimulus was in the range of 1-2 times threshold, cerebral application of the cholinergic antagonists blocked or greatly decreased the ability of lip-applied taste solutions to trigger FMP (5 of 8 trials). The cerebral feeding interneurons, some of which activate FMP when stimulated intracellularly, are excited by small pulses of ACh applied directly to the cell body from an ACh-filled micropipette. A pulse of ACh that activates several of the feeding interneurons simultaneously triggers FMP. The data suggest that under certain stimulus conditions an obligatory set of cholinergic synapses onto the feedininterneurons must be activated for taste inputs to trigger ingestion. The determination of ACh's action within the feeding control system is necessary for understanding how enhanced cholinergic transmission leads to prolonged associative memory retention (Sahley, et al., 1986). 相似文献
35.
Conversion of phosphatidylglycerol to lyso(bis)phosphatidic acid by alveolar macrophages 总被引:1,自引:0,他引:1
We report here studies of the synthesis of lyso(bis)phosphatidic acid [L(b)PA] by normal and BCG-elicited rabbit alveolar macrophages. This study was prompted by our earlier observations that 1) alveolar macrophages did not synthesize L(b)PA de novo despite its abundance in these cells, 2) BCG-elicited cells contained only one-quarter the amount of L(b)PA as normal cells, and 3) the turnover of arachidonate in L(b)PA led to hydroxyeicosatetraenoic acid and leukotriene synthesis. We found that exogenous phosphatidylglycerol (PG) was specifically converted to L(b)PA by both types of cells although BCG-elicited cells had only one-quarter the synthetic capacity of normal cells. Other phospholipids were found to become cell associated but were not significantly metabolized. Both glycerol moieties and the phosphate were incorporated into the product L(b)PA. However, substitution of the ester with an alkyl linkage in position 1 blocked the conversion of PG to L(b)PA. Most of the alkylphosphatidylglycerol was converted to phosphatidylcholine and phosphatidylethanolamine. This result implied that catabolism of the acyl group in position 1 was essential for L(b)PA synthesis. Because alveolar macrophages are present in a surfactant-rich milieu, we suggest that surfactant provides a source of PG for macrophage synthesis of L(b)PA in situ. It is interesting that the surfactants from rabbits challenged with BCG have a significant decrease in PG content. 相似文献
36.
Both phytohaemagglutinin and antibodies to the CD3 molecule induced proliferation and phosphoinositide hydrolysis in human peripheral-blood T lymphocytes, but the magnitude of the inositol phosphate response was small and the rate of accumulation slow [significant increases in Ins(1,4,5)P3 were observed only after 10 min]. Hence this response differs from the well-characterized Ins(1,4,5)P3 responses of many other systems. This slow response, its abrogation in Ca2+-depleted medium, the slow and maintained increase in Ca2+ as measured by Quin-2, and the ability of the Ca2+ ionophore A23187 to stimulate Ins(1,4,5)P3 accumulation all suggest that the increase in Ins(1,4,5)P3 occurs, at least in part, as a result of receptor-mediated Ca2+ influx in mitogen-stimulated T lymphocytes. 相似文献
37.
Solvation effects 总被引:1,自引:0,他引:1
38.
Summary The ultrastructure and density of chloride cells in the gill, opercular epithelium, and opercular skin of the euryhaline self-fertilizing fish Rivulus marmoratus (Cyprinodontidae) were studied with electron and fluorescence microscopy. R. marmoratus raised from birth in 1, 50, 100, and 200% seawater were compared. Chloride cells from fish raised in each of the four salinities exhibited an invaginated pit structure at the apical crypt. Multicellular complexes were present in the 1% seawater group and in those fish raised in higher salinities where elaborate interdigitations were seen between cells. Chloride cells from gills of fish raised in 200% seawater had a significantly higher percentage of their cytoplasmic volume composed of mitochondria than did those from fish raised in 1% seawater (69.9% vs 37.4%). The opercular skin and opercular epithelium had the same density of chloride cells (4.2×104-4.5×104 chloride cells/cm2), and this number did not vary significantly with increased salinity. The opercular skin thus appears far more responsive to environmental salinity than the opercular epithelium. Chloride cells from the opercular epithelium of fish raised in 200% seawater were found to be 39% larger than those from fish raised in 1% seawater, whereas the chloride cells from the opercular skin of the 200% seawater group were 107% larger than those from the 1% seawater group. 相似文献
39.
The availability of light, CO2 and NH4-N interacted to controlbuoyancy and growth of the gas vacuolate blue-green alga, Anabaenaflos-aquae. At high light intensities algal growth rates werehigh; however, the alga was non-buoyant regardless of the availabilityof CO2 or NH4-N. The mechanism for buoyancy loss involved increasedcell turgor pressures at higher light intensities which resultedin collapse of gas vacuoles. At lower light intensities algalgrowth rates and cell turgor pressures were reduced and buoyancywas controlled by the availability of CO2 and inorganic nitrogen.Carbon dioxide limitation increased buoyancy, while reducedinorganic nitrogen availability reduced buoyancy. Mechanismsfor buoyancy regulation at low light intensities involved changesin cellular C/N ratios which appeared to affect the rate ofsynthesis and accumulation of protein-rich gas vacuoles. Algalspecific growth rates were combined with buoyancy data to forma single index (µbloom) to the rate of surface bloom formationof A.flos-aquae as a function of the availability of light,CO2 and NH4-N. The bloom formation index was enhanced with decreasedavailability of light and CO2, and increased availability ofNH4-N. 相似文献
40.
Testing of Arg-8-gonadotropin-releasing hormone-directed antisera by immunological and immunocytochemical methods for use in comparative studies 总被引:1,自引:0,他引:1
Three polyclonal antisera raised in rabbits against the mammalian molecular form of gonadotropin-releasing hormone (GnRH) were tested in enzyme-linked immunosorbent assays for crossreactivity with naturally occurring GnRHs and with GnRH analogues. Antisera were then tested immunocytochemically in order (i) to identify amino acids essential for the binding of each antiserum, and (ii) to evaluate the specificity of the immunocytochemical reaction in brain sections from various species of cyclostomes, amphibians, reptiles, and birds. Antiserum GnRH 80/1, recognizing mainly a discontinuous determinant including the NH2- and COOH-termini, crossreacts with GnRHs the molecular bending of which enables the spatial approach of both terminal amino acid residues. Antiserum GnRH 80/2, by requiring the COOH-terminus for binding and not tolerating substitutions by aromatic amino acids in the middle region of the molecule, recognizes chicken I GnRH, however, not the salmon form. The use of this antiserum is appropriate in species synthesizing the mammalian and/or the chicken I form of GnRH. GnRH antiserum 81/1 is specific mostly for mammalian GnRH. The results obtained by ELISAs are confirmed by immunocytochemical studies. A comparison between the results obtained in ELISA and in immunocytochemistry involving mammalian-, chicken I-, chicken II-, salmon-, and lamprey-directed GnRH antisera resulted in the following conclusions: (1) An antiserum recognizing the discontinuous antigen determinant including both NH2- and COOH-termini may be reactive in most vertebrate brain sections thus being appropriate for phylogenetically directed immunocytochemical studies. (2) Moreover, this discontinuous determinant seems to be immunocytochemically reactive in all parts of the neurons in the GnRH system, whereas, in some species, determinants located in the middle region of the molecule(s) tend to become reactive only during the axonal transport. (3) A crossreaction between tissue-bound antigen and antibodies recognizing the above cited discontinuous determinant indicates an appropriate bending of the molecule even in case of severe molecular differences, e.g., in lamprey form of GnRH. (4) It follows that in phylogenetic studies, an immunologically well characterized antiserum can be substituted for a species-directed antiserum. 相似文献