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1.
Operational and constructional details are given of a relativelysimple and inexpensive chemostat designed for the continuousculture of plant cells in suspension. This apparatus permitscontrol of the growth rate of sycamore, Acer pseudoplatanusL. cells in steady-state conditions. By alteration of the rateof input of medium different steady-state growth rates wereobtained over a wide range (mean doubling times from 182 h to36 h). In order to establish a growth-limiting nutrient thetime course of nutrient uptake in batch culture was measured.In batch culture the maximum growth obtained was proportionalto the initial concentration of phosphate when this was belowa concentration of 17 µg P per ml (as phosphate). It isalso shown in chemostat culture that the steady-state cell densityis proportional to the phosphate concentration in the mediumwhen this is below 17 µg P per ml (as phosphate). Phosphatewas therefore established to be the growth rate-limiting nutrientin chemostat culture at a concentration of 85 µgP per ml (as phosphate). 相似文献
2.
Quantitative Aspects of Leaf Acid Phosphatase Activity and the Phosphorus Status of Tomato Plants 总被引:1,自引:0,他引:1
The relation between tomato leaf acid phosphatase activity andleaf tissue P content has been examined, and a study made ofthe effects of leaf development, variation in nitrogen supply,and variation in the growing medium on this relationship. Tomatoplants were grown in sand and given various concentrations ofphosphate. Plants were also grown for an initial period in peatcontaining an adequate level of phosphate, then transferredto peat to which was added 0 or 2.3 kg superphosphate m3and supplied with either 50 of 300 µg N ml1. Expressed on a unit tissue f. wt basis, acid phosphatase activityin the control plants in sand (given 41 µg P mlminus;1)was highest in extracts from the expanding leaves and decreasedwith leaf maturity. However, when given a reduced supply ofphosphate, the enzyme activity in the more mature leaves wasequal to, or greater than, that in the expanding leaves. Thephosphatase activity increased first in the young, fully-expandedleaves and in the mature leaves (with 4.1 µg P ml1),but did not increase in the expanding leaves until the supplywas restricted to 2.1 µg P ml1. On closer examination,the increase in enzyme activity appeared to be associated withthe P level in the leaf tissues, the activity increasing whenthe level fell below about 0.25 per cent (g P per 100 g drywt tissue). The same relation was found with the plants grownin peat, and was independent of the concentration of nitrogensupplied to the plants. The fully expanded leaves showed the best enzyme response whenthe phosphate supply was restricted and the activity reflectedclosely the local levels of tissue P. The assay of the enzymein unpurified leaf extracts is simple and rapid, and could beused in a test to detect P-deficiency in tomato plants. Lycopersicon esculentum L, tomato, acid phosphatase activity, phosphorus status 相似文献
3.
Genetic studies of nicotine addiction in mice have utilizedthe oral self-administration model. However, it is unclear ifstrain differences in nicotine consumption are influenced byvariation in bitter taste sensitivity. We measured both nicotineconsumption and nicotine brief-access licking behavior in severalcommonly used inbred strains of mice that were previously shownto differ in nicotine consumption. A/J (A), C57BL/6J (B6), andDBA/2J (D2) mice were given a 2-bottle choice test with a singleconcentration of nicotine (75 µg/ml; nicotine vs. water).Mice of these strains were also tested with a range of nicotineconcentrations (5–400 µg/ml) using a brief-accesstest, which measures orosensory response and minimizes postingestiveeffects. Although B6 mice consumed more 75-µg/ml nicotinethan A or D2 mice in the 2-bottle test, these strains did notdiffer in level of aversion to nicotine when tested with thebrief-access procedure. Strain differences in orosensory responseto nicotine were not found; yet, differences emerged duringthe 2-bottle tests. This study provides evidence that variationin intake level of nicotine is likely not due to differencesin taste or trigeminal sensitivity but likely due to postingestivefactors. 相似文献
4.
Ten species of Aspergillus isolated from soil samples collected from different locations in the Indian Himalayan region have been studied for their
growth requirements and tricalcium phosphate solubilization at different temperatures. The Aspergillus species could grow at low temperature and tolerated a wide range of pH. Phosphate solubilization by various Aspergillus species ranged between 374 μg/ml (A. candidus) to 1394 μg/ml (A. niger) at 28°C, 33 μg/ml (A. fumigatus) to 2354 μg/ml (A. niger) at 21°C, 93 μg/ml (A. fumigatus) to 1452 μg/ml (A. niger) at 14°C, and 21 μg/ml (A. wentii) to 83 μg/ml (A. niger) at 9°C. At 21 and 28°C, phosphate solubilization showed a decrease within 4 weeks of incubation, whereas at 9°C and 14°C,
it continued further up to 6 weeks of incubation. In general, phosphate solubilization by different Aspergillus species was recorded at a maximum of 28°C or 21°C; biomass production was favored at 21°C or 14°C. Conversely, A. nidulans and A. sydowii exhibited maximum phosphate solubilization at 14°C and produced maximum biomass at 21°C. Data suggest that suboptimal conditions
(higher or lower temperature) for fungal growth and biomass production were optimal for the production of metabolites involved
in phosphate solubilization. Significant negative correlations were obtained between pH and phosphate solubilization for eight
species at 28°C, for seven at 21°C, and for nine at 14°C. Extracellular phosphatase activity was exhibited only in case of
A. niger, whreas intracellular phosphatase activity was detected in all species, the maximum being in A. niger. Statistically significant positive or negative correlations were obtained between phosphate solubilization and other parameters
in most cases at different temperatures. 相似文献
5.
Seasonal uptake and regeneration of inorganic nitrogen and phosphorus in a large oligotrophic lake: size-fractionation and antibiotic treatment 总被引:3,自引:0,他引:3
Uptake and regeneration of inorganic N and P in oligotrophicFlathead Lake (Montana) were measured with 15N and 32P incorporationand dilution experiments, six times over a seasonal cycle. Theannual mean molar N P uptake ratio at ambient concentrationswas 13 9 (range = 4 834.2); uptake of nitrate, ammoniumand phosphate were always below saturation indicating both Nand P deficiency Organisms >280 µm were responsiblefor 060% of ammonium and 040% of phosphate regeneration,40100% of the ammonium and 3498% of phosphateregeneration occurred in the <3 µm fraction The <3µm fraction accounted for 770% of the ammoniumand 664% of the phosphate uptake. Results from antibiotictreatments indicated that both prokaryotic and eukaryotic ammoniumuptake was important, and that eukaryotes accounted for 5398%of the ammonium regeneration. During thermal stratification,heterotrophic ammonium and phosphate regeneration by organisms>3 µm supplied much of the inorganic N and P in theepilimnion. Estimated rates of allochthonous and diffusive (i.enew) ammonium, nitrate and phosphate input were<5% of biotic regeneration. These results suggests that (i)both N and P dynamics should be considered when examining nutrientregulation of primary productivity of oligotrophic lakes, (ii)bacteria probably compete with phytoplankton for both ammoniumand phosphate, (iii) biotic regeneration is the main sourceof nutrients to the epilimnion during stratification, and (iv)crustacean zooplankton were relatively unimportant sources ofregenerated ammonium and phosphate. 相似文献
6.
The African chironomid Polypedilum vanderplanki exhibits anhydrobiosis,i.e., the larvae can survive complete desiccation. Recoveryrate and trehalose content were investigated in larvae desiccatedslowly or at a rate more than 3 times faster. Upon slow desiccation(evaporation rate 0.22 ml day1) larvae synthesized 38µg trehalose/individual before complete desiccation, andall of them recovered after rehydration, whereas larvae thatwere dehydrated quickly (evaporation rate 0.75 ml day1)accumulated only 6.8 µg trehalose/individual and noneof them revived after rehydration. In the pools that are theirnatural habitat P. vanderplanki larvae make tubes by incorporatingdetritus or soil with their sticky saliva. This tubular structureis a physical barrier not only to protect the larva from naturalenemies but also induces successful anhydrobiosis by reducingthe dehydration rate. When larvae were dehydrated with 100 µldistilled water (DW) in soil tubes, they accumulated 37 µgtrehalose/individual and more than half of them could reviveafter rehydration, whereas larvae without tubes accumulatedlower level of trehalose and none recovered after rehydration. 相似文献
7.
《Saudi Journal of Biological Sciences》2021,28(12):7257-7268
IntroductionPiper crocatum Ruiz & Pav (P. crocatum) has been reported to accelerate the diabetic wound healing process empirically. Some studies showed the benefits of P. crocatum in treating various diseases but its mechanisms in diabetic wound healing have never been reported. In the present study we investigated the diabetic wound healing activity of the active fraction of P. crocatum on wounded hyperglycemia fibroblasts (wHFs).MethodsBioassay-guided fractionation was performed to get the most active fraction. The selected active fraction was applied to wHFs within 72 h incubation. Mimicking a diabetic condition was done using basal glucose media containing an additional 17 mMol/L D-glucose. A wound was simulated via the scratch assay. The collagen deposition was measured using Picro-Sirius Red and wound closure was measured using scratch wound assay. Underlying mechanisms through p53, αSMA, SOD1 and E-cadherin were measured using western blotting.ResultsWe reported that FIV is the most active fraction of P. crocatum. We confirmed that FIV\(7.81 µg/ml, 15.62 µg/ml, 31.25 µg/ml, 62.5 µg/ml, and 125 µg/ml) induced the collagen deposition and wound closure of wHFs. Furthermore, FIV treatment (7.81 µg/ml, 15.62 µg/ml, 31.25 µg/ml) down-regulated the protein expression level of p53 and up-regulated the protein expression levels of αSMA, E-cadherin, and SOD1.Discussion/conclusionsOur findings suggest that ameliorating collagen deposition and wound closure through protein regulation of p53, αSMA, E-cadherin, and SOD1 are some of the mechanisms by which FIV of P. crocatum is involved in diabetic wound healing therapy. 相似文献
8.
When seedlings of lettuce and turnip were grown in nutrientsolutions containing different concentrations of linuron, theconcentration in the shoot at the time when toxicity symptomsappeared was related to the solution concentration. With lettuce,for example, symptoms were recorded after 7 d at 0.15 µg/mland the shoot concentration was 2.7 µg/g fresh wt. At0.06 µg/ml, symptoms appeared after 10 d and the shootconcentration was then 1.1 µg/g fresh wt. If grown fordifferent periods in solutions containing linuron and then transferredto fresh nutrient solutions containing no herbicide, turnipor lettuce seedlings which had accumulated 0.70.8 µglinuron/g fresh wt developed toxicity symptoms 4 to 6 d later.Seedlings were also treated with linuron after they had grownfor different periods in control nutrient solutions. The shootconcentrations attained before toxicity symptoms appeared werehigher in those seedlings which were larger when herbicide treatmentbegan. These results show that the herbicide concentration insolution, time of exposure, and age of seedling are interrelatedin determining linuron phytotoxicity. 相似文献
9.
Wada Kojiro; Marumo Shingo; Ikekawa Nobuo; Morisaki Masuo; Mori Kenji 《Plant & cell physiology》1981,22(2):323-325
Brassinolide, a new plant growth-promoting steroid lactone,and its synthetic analog, homobrassinolide, showed strong activityin stimulating the lamina inclination of rice plants at verylow concentrations of 0.0005 and 0.005 µg/ml, respectively,whereas IAA showed only a weak effect on the lamina inclinationat 50 µg/ml. Thus, the lamina inclination test is usefulas a highly sensitive bioassay for brassinolide and relatedcompounds. (Received November 26, 1980; Accepted December 22, 1980) 相似文献
10.
In vitro activity of a new triazole antifungal agent,Sch 56592, against clinical isolates of filamentous fungi 总被引:6,自引:0,他引:6
Sch 56592 is a new triazole derivative that possesses potent, broad-spectrum antifungal activity. We evaluated the in vitroactivity
of Sch 56592 compared with that of itraconazole, amphotericin B and 5-fluorocytosine against 51 clinical isolates of filamentous
fungi, including Aspergillus flavus(10), A. fumigatus(12), Fusariumspp. (13), Rhizopus spp. (6), Pseudallescheria boydii(5),
and one isolate each of Acremoniumspp., A. niger, A. terreus, Paecilomycesspp., and Trichodermaspp. In vitrosusceptibility
testing was performed using the microdilution broth method outlined in the NCCLS 27-A document. Sch 56592 was highly active
against A. flavus(MIC90, 0.25 μg/ml), A. fumigatus(MIC90, 0.12 μg/ml), P. boydii(MIC50, 1 μ/ml) and Rhizopusspp (M1C50, 1 μg/ml). By comparison with itraconazole, Sch 56592 was four- to eight-fold more active against isolates of Aspergillusand
both compounds showed equipotent in vitroactivity against P. boydiiand Rhizopusspp. Sch 56592 was four- to 16-fold more active
than amphotericin B against Aspergillusspp. and P. boydiiand both antifungal drugs displayed similar activity against Rhizopusspp.
Overall, Sch 56592 showed good in vitroactivity against all isolates tested (MIC, ≤ 2 μg/ml) except isolates of Fusarium(MIC
range, 1–>4 μg/ml). On the basis of these data Sch 56592 has promising activity against Aspergillus spp. and other species
of filamentous fungi that are likely to be encountered clinically. Additional in vitroand in vivostudies are warranted.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
Phosphorus utilization by Asterionella formosa Hass 总被引:6,自引:0,他引:6
Observations have been made on the relationship in Lake Windermerebetween the growth of Asterionella formosa and the concentrationof dissolved phosphate. Asterionellaformosa has also been grownin culture and the amount of phosphorus required by this organismhas been determined. These experiments have shown that: (1) Asterionella can take up and store in reserve phosphorusfrom concentrations below those found in phosphorus-poor lakes(i.e. below 1 µg.P/l.). (2) Growth can continue in phosphorus-deficient media by makinguse of such reserves, cell phosphorus being steadily reduced. (3) The limiting requirement per cell of phosphorus is veryminuteabout 006µg P/106 cells/1, so thatinitial concentrations as low as rog.P/l. can theoreticallyproduce a population of some i6 x io6 cells/l. before limitationby phosphorus deficiency. This has been realized in culture.The behaviour of Asterionella formosa growing in nature hasbeen found to conform with that found in culture. It is concludedfrom such observations that phosphorus deficiency is unlikelyto provide a limit to growth of Asterionella in Windermere,despite the very low initial concentration of dissolved phosphate.Further experiments have shown that Asterionella cells low inphosphorus can rapidly take up added phosphate from lake waterbut not from distilled water. Some factors which affect therate of phosphate uptake of depleted cells are investigated,and attempts have ben made to throw some light on the natureof the apparent difference between lake water on the one handand distilled water and a number of artificial lake waters onthe other. No conclusion is reached on the reason why Asterionellacells behave differently in lake water and in artificial media. 相似文献
12.
13.
The increase of -amylase activity in embryoless rice endosperminduced by the addition of gibberellin A3 was examined undervarious conditions with an aim to establish a bioassay methodfor gibberellins. Sterilized embryoless rice endosperms were incubated in a testtube containing 0.21.0 ml of test solution for 4 daysat 30. -Amylase activity in the endosperm was determined bymeasuring digestion of added starch. The increase of amylaseactivity during the incubation was not affected by the additionof various vitamins, amino acids, organic acids, protease, sucrose,indoleacetic acid or kinetin. Helminthosporol, helminthosporicacid and sclerin (110 µg/ml) had weak promotingeffects. Under appropriate conditions, 105 µg/mlof gibberellin A3 could be detected. In double logarithmic plot,the increase in the enzyme activity was proportional to thegibberellin A3 concentration in the range from 105 to102 µg/ml. (Received April 13, 1966; ) 相似文献
14.
Various mechanicalstimuli increase the intracellular Ca2+ concentration([Ca2+]i) in vascular smooth muscle cells(VSMC). A part of the increase in [Ca2+]i isdue to the release of Ca2+ from intracellular stores. Wehave investigated the effect of mechanical stimulation produced bycyclical stretch on the release of Ca2+ from theintracellular stores. Permeabilized VSMC loaded with 45Ca2+ were subjected to 7.5% average (15%maximal) cyclical stretch. This resulted in an increase in45Ca2+ rate constant by 0.126 ± 0.0035. Inhibition of inositol 1,4,5-trisphosphate (IP3),ryanodine, and nicotinic acid adenine dinucleotide phosphate channels(NAADP) with 50 µg/ml heparin, 50 µM ruthenium red, and 25 µMthio-NADP, respectively, did not block the increase in45Ca2+ efflux in response to cyclical stretch.However, 10 µM lanthanum, 10 µM gadolinium, and 10 µMcytochalasin D but not 10 µM nocodazole inhibited the increase in45Ca2+ efflux. This supports the existence of anovel stretch-sensitive intracellular Ca2+ store in VSMCthat is distinct from the IP3-, ryanodine-, and NAADP-sensitive stores. 相似文献
15.
Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (45µm diameter) alone or in combination with Peridinium trochoideum(1618 µm diameter) at concentrations of 0.150.70mm3 x 11. Grazing rates (ml x zooid1 x 24 h 1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC1x 24 h1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (106 µm3x zooid1 x 24 h1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC1 x 24 h1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m3) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day.
1Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5 相似文献
16.
Dillon PF Root-Bernstein RS Lieder CM 《American journal of physiology. Cell physiology》2006,291(5):C977-C984
Ascorbate has previously been shown to enhance both 1- and 2-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to 1- and 2-adrenergic receptors. Physiological concentrations of ascorbate (50 µM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 µM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 µM histamine (5500 µM ascorbate) and 0.3 µM histamine (15500 µM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37°C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 µg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 µM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min·µg protein1·ml1, compared with rates for transfected ANG II membrane (0.055 min·µg protein1·ml1), untransfected membrane (0.052 min·µg protein1·ml1), creatine kinase (0.0082 min·µg protein1·ml1), keyhole limpet hemocyanin (0.00092 min·µg protein1·ml1), and osmotically lysed aortic rings (0.00057 min·µg wet weight1·ml1). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state. molecular complementarity; vitamin C; seven-transmembrane-spanning membrane receptors 相似文献
17.
Sialyl-Tn-KLH, glycoconjugate analysis and stability by high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) 总被引:1,自引:1,他引:0
The quantitation of sialyl-Tn (STn) conjugated to keyhole limpethaemocyanin (KLH) can be determined by quantitating the amountof N-acetylneuraminic acid (NANA) released by acid or enzymaticdigestion. An optimal 0.1 N H2SO4 acid hydrolysis at 80°Cresults in quantitative release of NANA with minimal loss. Arapid isocratic method for the quantitation and separation ofNANA is described using high-pH anion-exchange chromatographyand pulsed amperometric detection (PAD). Multiple injectionof NANA standard and/or samples containing protein led to adecrease in the PAD response which was corrected by additionof internal standard, -2-keto-3-deoxyoctonate (KDO). The ratioof NANA/KDO peak area or peak height gives a linear responsewith increasing amount of NANA in the range 2.520 µg/ml(r2 = 0.99). The limit of quantitation (LOQ) for NANA usingthis isocratic method is 1.9 µg/ml ({small tilde}160 pmol/25µl injection). Based on the multiple determination theglycoconjugate, STn-KLH, showed a NANA content of 2.9% (w/w).Acid hydrolysis and the sialidase treatment of STn-KLH bothyielded a similar NANA content. The carrier protein, KLH, showedthe absence of NANA. The stability of glycoconjugate STn-KLHwas monitored by a gradient method which separated possibledegradation products STn-crotyl, NANA and GalNAc. Subjectingthe glycoconjugate STn-KLH to various stress conditions of temperature,pH and oxidation does not result in any release of sialic acid,GalNac and STn-crotyl group. high-pH anion-exchange chromatography mono-saccharide analysis pulsed amperometric detection sialyl-Tn stability of glycoconjugate 相似文献
18.
The role of phosphorus on planktonic production of the Gironde plume waters in the Bay of Biscay 总被引:8,自引:0,他引:8
More and more studies emphasize the status of phosphorus (P)as the principal limiting nutrient of phytoplankton growth,especially in coastal waters under the influence of freshwaterdischarges. The purpose of the present paper is to investigatethe role of P on planktonic production in the waters influencedby the Gironde discharges; the Gironde being one of the twolargest rivers on the French Atlantic coast. The survey is basedon several cruises made in 1998 and 1999. Two different patternswere observed for waters with salinity below and above 34.5.For waters with salinity < 34.5, P was found to be the firstlimiting nutrient of winter and spring phytoplankton blooms,based on undetectable phosphate (< 20 nM), high NO3 : PO4ratios, typically > 100 : 1, short phosphate turnover time(1 to 2 h), high alkaline phosphatase activities (mean of 176nM h-1 in late May 1999) and ultimately great increases of chlorophylla (Chl a) and primary production in phosphate-enriched samplesrelative to controls. This limitation could be partly explainedby the Gironde nutrient supplies, which were phosphate deficientcompared with the mineral nitrogen(Nmin : PO4 was > 40 withina salinity range 1633). In summer, corresponding to theperiod of low influence of Gironde supplies (low runoff anda spreading effect of the plume), phytoplankton growth wouldbe controlled by both P and nitrogen (N), according to low nitrateand the major effect of combined P+N (NH4) enrichment on Chla and primary production compared with the addition of N orP singly. In early October, after the first autumn gales, themixed layer was enriched with a sufficient supply of nutrientsto support exponential phytoplankton growth for 4 days in enclosures.The pattern was different for waters at the limit of the Girondeplume and Atlantic oceanic waters (within salinity range 34.535.4).P would not be the single limiting nutrient of winter bloomsand spring phytoplankton growth since low phosphate, and alsolow nitrate and silicate, availability were recorded and phosphateaddition alone had no effect on phytoplankton biomass and productionin bioassays. The early P limitation of winter blooms had consequencesfor the phytoplankton community structure in the Gironde plumewaters (salinity < 34.5). Whereas major cells of these bloomswere greater than 20 µm in size, phytoplankton growthin spring and autumn was dominated by 320 µm (e.g.53% of Chl a in late April 1999) and < 3 µm cells (e.g.29% of Chl a). The decreasing size of phytoplankton cells isemphasized by the severe competition between bacteria and algaefor phosphate, since bacteria dominated phosphate uptake inspring (e.g. 87% in late April, 77% in late May). Bacteria tendedto have greater affinity for phosphate and seemed also to beP limited at certain times in spring, according to results fromphosphate enrichment bioassays in late May 1999. The alternativemethod for phytoplankton to obtain P would be the use of thedissolved organic phosphorus pool by alkaline phosphatase activity.According to the movement of 33P after initial labelling ofmicrobial populations and a subsequent cold chase, the majortransfer of P occurred from the bacterial to the dissolved fraction.We hypothesize that algae obtain part of its dissolved organicphosphorus from bacteria-originated organic phosphorus compounds. 相似文献
19.
Previously it was demonstrated that bacteria are capable of transforming soluble uranyl ion, U(VI), to insoluble uraninite,
U(IV); however, the rate for this transformation has not been determined. We report the kinetic coefficients for Desulfovibrio desulfuricans DSM 1924 grown in a continuous-flow chemostat where pyruvate was the electron donor and sulfate was the electron acceptor.
The medium was supplemented with 1 mM uranyl nitrate, and the chemostat flow rate ranged from 1.12 ml/h to 4.75 ml/h with
incubation at 28°C. The maximum rate of pyruvate utilization (k) was determined to be 4.7 days-1, while the half-velocity constant (K
s) was 127 mg/l. The yield coefficient (Y) of cells per mole of pyruvate oxidized was calculated to be 0.021 g, while the endogenous decay coefficient (k
d) was determined to be 0.072 days-1. More than 90% of U(VI) was transformed to U(VI) in the chemostat under the conditions employed.
Received: 7 September 1995/Received last revision: 10 January 1996/Accepted: 5 February 1996 相似文献
20.
Charan Nirmal B.; Carvalho Paula; Johnson Shane R.; Thompson William H.; Lakshminarayan S. 《Journal of applied physiology》1998,85(2):432-436
We studiedthe effects of aerosolized as well as intravenous infusion ofacetylcholine on bronchial blood flow in six anesthetized sheep.Intravenous infusion of acetylcholine, at a dose of 2 µg/kg, increased bronchial blood flow from 45 ± 15 (SE) to 74 ± 30 ml/min, and vascular conductance increased by 76 ± 22%. In contrast, aerosolized acetylcholine at doses of 2 and 20 µg/kg decreased bronchial vascular conductance by ~10%. At anaerosolized dose of 200 µg/kg, the bronchial vascular conductanceincreased by ~15%, and there was no further increase in conductancewhen the aerosolized dose was increased to 2,000 µg/kg. Pretreatmentof animals with a nitric oxide synthase inhibitor,N-nitro-L-argininemethyl ester hydrochloride, partially blocked the vasodilatory effectsof intravenous acetylcholine and completely blocked the vasodilatoryeffects of high-dose aerosolized acetylcholine. These data suggest thataerosolized acetylcholine does not readily penetrate the vascular wallof bronchial circulatory system and, therefore, has minimalvasodilatory effects on the bronchial vasculature. 相似文献