共查询到20条相似文献,搜索用时 112 毫秒
1.
The number of metabolically active bacteria was measured with nalidixic acid over two annual cycles at three depths in the epilimnion of hypertrophic Hartbeespoort Dam, South Africa. Concurrent measurements were made of water temperature, DOC, phytoplankton production of dissolved (EDOC) and particulate organic carbon, chlorophyll a and the uptake of glucose (Vmax). The objective was to determine the dominant factors correlated to the number of metabolically active bacteria and the relationship between active bacterial numbers and heterotrophic activity.The number of active bacteria was usually highest at the surface and ranged between 0.70 and 6.82 x 106 cells ml–1. The dominant factors correlated to the number of bacteria at the surface were water temperature (r = 0.65, n = 54, p<0.001), primary production (r = 0.53, n = 51, p<0.001) and EDOC (r = 0.37, n = 45, p = 0.005). Surface Vmax for glucose ranged between 0.11 and 4.0 µgC 1–1 h–1 and was positively correlated to the number of active bacteria (r = 0.61, n = 53, p<0.001). The specific activity index (10–12 µgC cell–1 h–1) varied between 80 and 2290 at the surface and was most strongly correlated to EDOC (r = 0.70, n = 48, p<0.001). Relationships between active bacterial numbers, water temperature, phytoplankton activity and glucose uptake were also found at two additional depths within the epilimnion. These data suggest that bacterial populations in nutrient enriched lakes contain a large number of metabolically active cells with high individual activity as a result of enhanced phytoplankton growth. 相似文献
2.
Density and distribution of bacterioplankton and planktonic ciliates in the Bering Sea and North Pacific 总被引:3,自引:0,他引:3
The total number of planktonic bacteria in the upper mixed layerof the Bering Sea during the late spring-early summer periodranged between 1 and {small tilde}4 x 106 ml1 (biomass1040mg C m3). In the northern Pacific, along 47526N,the corresponding characteristics of the bacterioplankton densityin the upper mixed water layer were: total number 12x 106 cells ml1 and biomass 1546mg C m3Below the thermocline at 50100 m, the density of bacterioplanktonrapidly decreased. At 300 m depth, it stabilized at 0.10.2x 106 cells ml1. The integrated biomass of bacterioplanktonin the open Bering Sea ranged between 1.2 and 3.6 g C m2(wet biomass 618 g m2) Its production per dayvaried from 2 to 23 mg C m3 days1 in the upper0100 m. The numerical abundance of planktonic ciliatesin this layer was estimated to be from 3 to l0 x 103 cells l1,and in the northern Pacific from 0.4 to 4.5 x 103 l2.Their populations were dominated by naked forms of Strombidium,Strombilidium and Tontonia. In some shelf areas, up to 40% ofthe total ciliate population was represented by the symbioticciliate Mesodinium rubrum. The data on the integrated biomassof basic groups of planktonic microheterotrophs are also presented,and their importance in the trophic relationships in pelagiccommunities of subarctic seas is discussed. 相似文献
3.
Pantoja Silvio; Gonzalez Humberto; Bernal Patricio A. 《Journal of plankton research》1989,11(3):599-604
Bacterial biomass (BB, acridine orange) and bacterial secondaryproduction (BSP, [3H]thymidine incubations) were measured forthe first time in Concepción Bay (37°35'S, 73°01'W).BB ranged from 1.8x106 to 22.5x106 cells ml1 (the lattervalue observed near to an industrial effluent), BSP from 0.27x106to 2.5x106 cell ml1 day1 and heterotrophic turnoverrates between 0.15 and 1.0 doublings day1. 相似文献
4.
Potential effects of abiotic factors on the abundance of autotrophic picoplankton in four boreal lakes 总被引:2,自引:0,他引:2
The seasonality of autotrophic picoplankton (APP) in four boreallakes of varying trophic state and light availability was studied.Red-fluorescing cyanobacteria (CyAPP) dominated the APP in threelakes, but in the fourth, most humic lake, Valkea Kotinen, eukaryoticpicoalgal cells (EuAPP) predominated. The most productive, leasthumic, and stratified lake (Ormajärvi) was the only onein which low numbers of orange-fluorescing cyanobacteria werepresent in winter (7 x 102 cells ml-1) and early spring (1 x102 cells ml-1) under the ice cover. The numbers of CyAPP didnot correspond to the trophic status of the lakes. The highestaverage and maximal numbers of CyAPP were recorded in shallowand moderately productive Jylisjärvi (6.2 x 105 cells ml-1)while the lowest number (8 x 104 cells ml-1) was recorded inthe deepest lake, Pääjärvi, with fairly similarwater quality. Light availability and water temperature seemedto be more important abiotic factors in regulating CyAPP andEuAPP density than nutrient concentrations. In the deepest lakes,light and temperature correlated very strongly with densityof CyAPP in spring, while in the shallowest lake this correlationonly occurred in autumn. Although light and temperature wereoccasionally significantly correlated with EuAPP cell density,no common trend throughout all the seasons (as seen for prokaryoticAPP) was found. 相似文献
5.
The population abundances and rates of biomass production ofheterotrophic nanoplankton (HNAN) in Georgia coastal waterswere evaluated by epifluorescence microscopy. HNAN populations(mostly non-pigmented microflagellates <10 µm in diameter)ranged from 0.3 x 103 cells ml1 in shelf waters 15 kmoffshore to 6.3 x 103 cells ml1 in waters 0.25 km fromthe coast. There was a strong correlation (r = 0.83) betweenHNAN and free bacterioplankton population abundances, but noapparent relation (r = 0.38) between HNAN and phototrophic nanopLankton(PNAN) abundances. HNAN biomass production in estuarine andnearshore shelf waters, as estimated from increases in HNANpopulations during laboratory incubations of natural water samples,ranged from 0.10 to 0.79 mg C m3 h3, with populationgeneration times of 9.7 to 26.5 h. There was a significant linearrelation (r = 0.95) between HNAN biomass and HNAN productivity.We calculated that HNAN may graze at least 30% to 50% of dailybacterioplankton production in Georgia coastal waters. 相似文献
6.
Grazing on bacteria by flagellates and cladocerans in lakes of contrasting food-web structure 总被引:4,自引:0,他引:4
We tested the hypothesis that grazing on bacteria would varybetween lakes with differing plankton community structures.Paul and Tuesday lakes (Gogebic County, MI) are respectivelydominated by piscivorous and planktivorous fish. Consequently,zooplankton in Paul are primarily large daphnids, while zooplanktonin Tuesday are primarily small cladocerans and copepods. Wemeasured flagellate grazing on bacteria using a fluorescentminicell method, while cladoceran grazing was estimated fromthe relationship between body length and filtering rate. Wepredicted that cladoceran grazing on bacteria would be higherin Paul, and flagellate grazing would be higher in Tuesday.Cladoceran grazing on bacteria was important in both lakes contraryto our initial expectation. Large populations of the small cladoceran,Bosmina longirostris, in Tuesday exerted a grazing pressure(0.1835x106 bacteria 11 h1) approximatelyequal to that of the large cladoceran, Daphnia pulex, in Paul(0.3430x106 bacteria 11 h1). Flagellategrazing was higher in Tuesday as predicted (range: Paul, 0.16x106bacteria 11 h1; Tuesday, 0.220x106 bacteria11 h1). However, there was not a simple relationshipbetween total abundance of flagellates and total grazing rates.High community grazing by flagellates occurred when attachedchoanoflagellates were present. These flagellates had higheringestion rates than free forms. We find no clear evidence thatdifferences in food-web structure between the two lakes influencethe process of grazing on bacteria. Instead, our results emphasizethe significance of cladocerans and attached flagellates asconsumers of bacteria in freshwater ecosystems. 相似文献
7.
Abundance, morphology and distribution of planktonic virus-like particles in two high-mountain lakes 总被引:5,自引:0,他引:5
Pina Sonia; Creus Andreu; Gonzaalez Nuria; Gironees Rosina; Felip Marisol; Sommaruga Ruben 《Journal of plankton research》1998,20(12):2413-2421
Direct counts of virus-like particles (VLP) by transmissionelectron microscopy revealed abundances of up to 3 x 107 ml1in the plankton of two remote high-mountain lakes in the Alpsand the Pyrenees. Most VLP were icosahedric without a tail,and with diameters between 40 and 90 nm, but very large oneswith diameters of up to 325 run were also observed. VLP outnumberedbacteria by a factor of 4.242.8 and bacterial cells wereinfected with large numbers (>50) of viral particles. Thisstudy constitutes the first report on aquatic viruses for alpinelakes and it suggests that they may be an important additionalsource of bacterial mortality in these systems. 相似文献
8.
A dual radioactive-labelled bacteria technique using Vibrio(DRLV), developed for laboratory studies on bacterivory, hasbeen refined for use at the concentrations of prey and predatorstypcially found at sea. Experiments with estuarine water collectedin spring and in autumn showed that bacterivorous nanoflagellates(HNF) (concentration 1.38±0.35x103 HNF ml1) ingested2.7±0.96 DRLV flagellate11 h1 at concentrationsof 0.82.2x106 DRLV ml1 in the presence of 2.04±0.68x106natural bacteria ml1. The method was also applied tosamples collected in October in the Celtic Sea, when on average1 ml of water from the surface layer contained 1.41±0.16x106natural bacteria, 14.6x103 cyanobacteria, 530±170 HNF,7.3±3.0x103 phototrophic nanoflagellates (1.54µm), 49.0±26.5 phototrophic dinoflagellates, 36.3±12.6heterotrophic dinoflagellates and 21.3±9.5 Leucocryptosmarina. Under these conditions the grazing rate in most samplesdid not exceed the coefficient of variation of the method (2%),although we estimate the grazing rate was -1.6 DRLV HNF1h1 and on one occasion a rate of 2.45 was recorded. Thegross growth efficiency for protein of -30% displayed by naturalHNF means that they could release about 相似文献
9.
Paoli A.; Karuza A.; de Vittor C.; del Negro P.; Umani S. Fonda 《Journal of plankton research》2006,28(3):325-335
Nowadays, it is recognized that only a fraction of aquatic bacteriaare actively growing, but there is little information aboutthe factors constraining their metabolism. Marine bacterioplanktoncan rapidly modify their metabolic activity level in responseto environmental changes. In this study, we focused on the dailychanges in abundance and activity of active bacterial fractionover a 20-day period preceded by intense rainfalls which slightlymodified water column conditions. Cells capable of reducingthe membrane-penetrable dye 5-cyano-2,3-ditolyl tetrazoliumchloride (CTC), estimated by epifluorescence microscopy, areconsidered very active (CTC+ bacteria). Total bacterial abundance(TBA) ranged from 0.8 to 2.4 x 109 cells L1, whereasCTC+ bacteria were more variable (1.69.2 x 107 cellsL1), accounting for 1.24.4% of TBA. Bacterialactivity (BA) quantified as the incorporation of [3H]-leucinevaried by more than one order of magnitude over the period (25.0662.5pmol L1 h1). BA was strongly related to CTC+ bacteria,suggesting that they were mainly responsible for the bacterialcommunity metabolism. Nevertheless, cell-specific activity,scaled to only CTC+ cells, was very high, suggesting that afraction of cells not detectably CTC+ may be able to assimilate[3H]-leucine. The correlation between salinity and TBA, CTC+bacteria and BA supported the hypothesis of the active roleof freshwater input in enhancing cell activity. Our resultssuggest that freshwater inputs rather than phytoplanktonic bloomsare able to induce shifts in bacterial metabolism over a timescale of days in the area studied. 相似文献
10.
Chloroplast DNA in Expanding Spinach Leaves 总被引:2,自引:0,他引:2
The proportion of chloroplast DNA in total DNA from spinachleaves has been measured using the second order reassociationkinetics of a 3H-labelled chloroplast DNA probe in total DNAextracts. There was no significant difference between the proportionof chloroplast DNA in the basal and distal halves of 2 cm leavesand in the distal halves of 5, 8, and 10 cm leaves. The meanof all the observations was 21.1 ± 0.7%. There was littlechange in the average total DNA content of cells from any ofthe leaves but cells from larger leaves contained 130170chloroplasts while cells from the basal half of 2 cm leavescontained about 20 chloroplasts which were smaller than thosefrom the larger leaves. Consequently the average number of copiesof the plastome per chloroplast in large leaves was about 30(5 x 1015 g DNA) and in the smaller chloroplasts in thebase of 2 cm leaves was 200 (32 x 1015 g DNA). Stainingwith the DNA fluorochrome 4, 6-diamidino-2 phenyl indole (DAPI)showed 1015 plastid nucleoid areas in chloroplasts oflarger leaves, suggesting there are 23 copies of theplastome per plastid nucleoid. 相似文献
11.
The standard synthetic culture medium (Stuart and Street, 1969)has been modified by adjustment of its initial pH to 6.4 andby the addition of gibberellic acid (0.25 mg/l) and of a mixtureof 15 L-amino acids formulated from an analysis of the conditionedmedium. The minimum effective density for the growth of sycamorecell suspensions in the standard medium is 915 x 103cells ml1, for the modified synthetic medium it is 2.0x 103 cells ml1, and for conditioned medium 1.01.25x 103 cells ml1. Using either conditioned medium (Stuart and Street, 1969) orthe modified synthetic medium it is demonstrated that the growthof cultures initiated at low density is enhanced by a volatilefactor released from actively growing cell suspensions. In presenceof conditioned medium and this volatile factor cultures canbe established from stationary-phase cells at a density of 6x 102 cells ml1. The volatile factor can be absorbedin 40 per cent w/v KOH but attempts to replace the factor byair containing carbon dioxide at concentrations up to 5 percent have so far been unsuccessful. 相似文献
12.
Differential filtration was used to apportion [32p]orthophosphate(P1) uptake to predominantly bacterial (<3 µm) or algal(>3 µm) components of Lake Kinneret microplankton.Bacteria generally showed preferential 32Pi uptake in comparisonwith algae. Nevertheless, in most cases, the relative proportionof 32P counts retained on 3 µm filters was greater thanthe proportion of 14C counts from heterotrophic bacterial incorporationof [14Clglucose, indicating that algae were competing for Piwith bacteria with some measure of success. Most time courseexperiments did not show any consistent transfer of 32P frombacteria to algae. The addition of a bacterial inhibitor (garamycin)caused a relative increase in the proportion of algal to bacterial32Pi uptake. Added organic P substrates lowered the amount of32Pi uptake and appeared to be preferentially utilized by bacteria.Apparent residence times for Pi in Lake Kinneret ranged from0.4 h (prior to overturn) to 17.4 h during bomothermy. Despitelow ambient Pi concentrations, P limitation in Lake Kinneretis not as extreme as in many other aquatic environments. 相似文献
13.
Abundance, size distribution and bacterial colonization of transparent exopolymeric particles (TEP) during spring in the Kattegat 总被引:3,自引:0,他引:3
The abundance, size distribution and bacterial colonizationof transparent exopolymeric particles (TEP) were monitored inthe Kattegat (Denmark) at weekly intervals throughout the spring(February-May) encompassing the spring diatom bloom. These recentlydiscovered particles are believed to be formed from colloidalorganic material exuded by phytoplankton and bacteria, and mayhave significant implications for pelagic flux processes. Duringthis study, the number concentration of TEP (>1 µm)ranged from 3 x 103 to 6 x 104 ml1 and the volume concentrationbetween 0.3 and 9.0 p.p.m.; they were most abundant in the surfacewaters subsequent to the spring phytoplankton bloom. The rangeof TEP (encased) volume concentration was similar to that ofthe phytoplankton, although at times TEP volume concentrationexceeded that of the phytoplankton by two orders of magnitude.The TEP size distribution followed a power law, with the abundanceof particles scaling with particle diameter(ß+1).The seasonal average estimate of ß (2.3) was not significantlydifferent from three, consistent with TEP being formed by shearcoagulation from smaller particles. However, date-specific estimatesof ß differed significantly from three, probably becauseTEP are fractal. All TEP were colonized by bacteria, and bacteriawere both attached to the surface of and embedded in TEP. Yetthe number of attached bacteria per TEP was related neitherto the surface area nor the volume, but rather scaled with TEPsize raised to an exponent of 相似文献
14.
Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer 总被引:5,自引:0,他引:5
Nagata Toshi; Takai Kenji; Kawanobe Kyoko; Kim Dong-Sup; Nakazato Ryoji; Guselnikova Nina; Bondarenko Nina; Mologawaya Oliga; Kostrnova Tatyana; Drucker Valentine; Satoh Yasuhiro; Watanabe Yasunori 《Journal of plankton research》1994,16(8):945-959
Autotrophic picoplankton were highly abundant during the thermalstratification period in late July in the pelagic area (waterdepth 5001300 m) of southern Lake Baikal; maximum numberswere 2 x 106 cells ml1 in the euphotic zone ({small tilde}15m). Unicellular cyanobacteria generally dominated the picoplanktoncommunity, although unidentified picoplankton that fluorescedred under blue excitation were also abundant (maximum numbers4 x 105 cells ml1) and contributed up to {small tilde}40%of the total autotrophic picoplankton on occasions. Carbon andnitrogen biomasses of autotrophic picoplankton estimated byconversion from biovolumes were 1484 µg C l1and 3.621 µg N l1. These were comparableto or exceeded the biomass of heterotrophic bacteria. Autotropicpicoplankton and bacteria accounted for as much as 33% of paniculateorganic carbon and 81% of nitrogen in the euphotic zone. Measurementsof the photosynthetic uptake of [l4C]bicarbonate and the growthof picoplankton in diluted or size-fractionated waters revealedthat 80% of total primary production was due to picoplankton,and that much of this production was consumed by grazers inthe <20 µ.m cell-size category. These results suggestthat picoplankton-protozoan trophic coupling is important inthe pelagic food web and biogeochemical cycling of Lake Baikalduring summer. 相似文献
15.
Abstract
In natural bacterioplankton assemblages, only a fraction of the total cell count is active, and, therefore, rates of bacterial
production should be more strongly correlated to the number of active cells than to the total number of bacteria. However,
this hypothesis has seldom been tested. Herein we explore the relationship between rates of bacterial production (measured
as leucine uptake) and the number of active bacteria in 14 lakes in southern Québec. Active bacteria are defined as those
cells capable of reducing the tetrazolium salt CTC to its fluorescent formazan; these cells were enumerated using flow cytometry.
Bacterial production varied two orders of magnitude in the lakes studied, as did the number of active bacteria, whereas the
total number of bacteria varied by only sixfold. The number and proportion of active bacteria were similar among lake strata,
but rates of bacterial production were highest in the epilimnion and lowest in the hypolimnion. As expected, bacterial production
was better correlated to the number of active cells, and bacterial growth rates calculated for active cells ranged from 0.7
to 1.8 day−1, on average threefold higher than those calculated on the basis of total bacterial abundance. Growth rates scaled to active
cells were, on average, similar among lake strata and did not show any pattern along a gradient of increasing chlorophyll
concentration, so there was no systematic change of bacterial growth rates with lake productivity. In contrast, growth rates
scaled to the entire bacterial assemblage were positively correlated to chlorophyll, were tenfold more variable among lakes
than growth rates of active cells, and showed larger differences among lake strata. Scaling bacterial production to either
the total number or the number of active cells thus results in very different patterns in bacterial growth rates among aquatic
systems.
Received: 12 July 1996; Accepted: 24 September 1996 相似文献
16.
We examined the generation time and the house renewal rate ofOikopleura dioica under various conditions. Animals were fedtwo flagellates, Isochrysis galbana and Tetraselmis sp., withconcurrent determination of the carbon contents of body andhouse to estimate house production. The generation time was6 days at 15°C, 4 days at 20°C and 3 days at 25°Cat both 25 and 30 p.s.u. with a food concentration of 4 x 104cells ml1. The carbon content of newly secreted housesranged from 0.5 to 0.8 µg, corresponding to 15.3 ±4.8% of body carbon. The house renewal rates increased withincreasing temperature and decreasing salinity. Food concentrationsranging from 100 to 16 x 104 cells ml1, body size andlight condition had no effect on house renewal rate. Cloggingof the inlet filter by adding the large diatom Ditylum sol causedan increase in house renewal rates. The total number and carboncontent of houses during an animal's lifetime ranged from 46to 53 houses and from 6.5 to 10.4 µg, respectively. Sincedaily house production calculated for the O. dioica populationcorresponded to 130290% of its biomass and daily discardedhouse materials corresponded to 4901100% of the biomass,this organism must play an important role as a producer of macroscopicaggregates. 相似文献
17.
Large Fraction of Dead and Inactive Bacteria in Coastal Marine Sediments: Comparison of Protocols for Determination and Ecological Significance 总被引:9,自引:4,他引:5 下载免费PDF全文
It is now universally recognized that only a portion of aquatic bacteria is actively growing, but quantitative information on the fraction of living versus dormant or dead bacteria in marine sediments is completely lacking. We compared different protocols for the determination of the dead, dormant, and active bacterial fractions in two different marine sediments and at different depths into the sediment core. Bacterial counts ranged between (1.5 ± 0.2) × 108 cells g−1 and (53.1 ± 16.0) × 108 cells g−1 in sandy and muddy sediments, respectively. Bacteria displaying intact membrane (live bacterial cells) accounted for 26 to 30% of total bacterial counts, while dead cells represented the most abundant fraction (70 to 74%). Among living bacterial cells, nucleoid-containing cells represented only 4% of total bacterial counts, indicating that only a very limited fraction of bacterial assemblage was actively growing. Nucleoid-containing cells increased with increasing sediment organic content. The number of bacteria responsive to antibiotic treatment (direct viable count; range, 0.3 to 4.8% of the total bacterial number) was significantly lower than nucleoid-containing cell counts. An experiment of nutrient enrichment to stimulate a response of the dormant bacterial fraction determined a significant increase of nucleoid-containing cells. After nutrient enrichment, a large fraction of dormant bacteria (6 to 11% of the total bacterial number) was “reactivated.” Bacterial turnover rates estimated ranged from 0.01 to 0.1 day−1 but were 50 to 80 times higher when only the fraction of active bacteria was considered (on average 3.2 day−1). Our results suggest that the fraction of active bacteria in marine sediments is controlled by nutrient supply and availability and that their turnover rates are at least 1 order of magnitude higher than previously reported. 相似文献
18.
A strain of Coleps hirtus (Ciliophora, Prorodontida) was isolatedfrom the epilimnion of monomictic Lake Kinneret. Growth of thisciliate was tested in response to 12 species of planktonic algaeand seven species of cultured bacteria from lake isolates whichwere offered as food. Eight species of algae (one Cryptophyceaeand seven Chlorophyceae) and four bacteria supported good toexcellent growth of C.hirtus. Growth rates (µ) and doublingtimes (DT) ranged from 0.008 to 0.029 h1 and from 23.9to 90.8 h respectively. C.hirtus was able to grow on bacteriaat concentration levels as low as 28 x 105 cells ml1.No correlation was observed between growth rate of C.hirtusand cell volume of the prey.
aPresent address: Istituto di Ecologia, Universita di Parma,43100 Parma, Italy 相似文献
19.
Association with resource-rich particles may benefit a numberof planktonic species in oligotrophic, open-ocean regimes. Thisstudy examined communities of microbes and zooplankton associatedwith colonies of the cyanobacterium Trichodesmium spp. in theSargasso Sea. Trichodesmium colonies and seawater controls werecollected near Bermuda using SCUBA during September 1995, andJune, July and August 1996. Organisms associated with the coloniesand those in the surrounding seawater were enumerated usinglight and fluorescence microscopy. We found that 85% of theTrichodesmiumpuff and tuft colonies examined harbored associated organisms.Associated organisms included bacteria (rod and coccoid), fungi,pennate diatoms, centric diatoms, heterotrophic and autotrophicdinoflagellates, chrysophytes, hypotrich ciliates, amoebae,hydroids, juveniles and nauplii of harpacticoid copepods, andjuvenile decapods. The most common associates (in addition tobacteria) were dinoflagellates (present in 74% of the coloniesexamined), amoebae (50%), ciliates (24%), and diatoms (24%).Numbers of bacteria per colony volume averaged 8.2x108 bacteriaml-1 (range = 8.1x107 3.5 x109 bacteria ml-1), and thedensity of associated microzooplankton and metazoans averaged6.8x104 organisms ml-1 (range = 0 3.6 x106 organismsml-1). Associates of Trichodesmium colonies were enriched bytwo to five orders of magnitude over plankton in the surroundingwater. This unique habitat allows for the association of primarilybenthic ciliate, diatom and copepod species and could contributesignificantly to plankton heterogeneity in the open-ocean. Thedistribution of associated organisms was affected by samplecharacteristics such as colony morphology, mucoid matrix structureand colony integrity. The influence of these factors indicatesthat succession or competition between heterotrophic microorganismsultimately determines Trichodesmium microcommunity structure.Similar processes could regulate microbial and metazoan communitiesassociated with other resource-rich microenvironments, suchas marine snow particles. 相似文献
20.
[2-14C]-uridine is rapidly taken up by sycamore cells in suspensionculture. A proportion of the radioactivity enters RNA withoutmeasurable delay, whilst the remainder equilibrates with a largepool of phosphorylated compounds, the major radioactive componentof which is 5'-UMP. Both the uracil and cytosine residues ofRNA receive label from [14C]-uridine and, when the cells aresupplied with high concentrations of uridine, these bases arederived almost exclusively from the nucleoside. [14C]-uridine is incorporated into RNA at all stages of thegrowth cycle of batch cultures; its continuing incorporation,when the total RNA content of the cells is rapidly decreasing,indicates a high rate of turnover of the total RNA. Long-termlabelling experiments also indicate turnover of RNA during thephase of active cell division and suggest that a large proportionof the degradation products are not re-utilized for RNA synthesis. Sycamore cells degrade [2-14C]-uridine with release of 14CO2.The proportion degraded increases from 25 per cent at an externaluridine concentration of 106M to 75 per cent at 103M. Despite this, nucleic acids are the only macromolecules thatreceive a significant amount of radioactivity from [2-14]C-uridine. 相似文献