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1.
Greenhouse-grown cut flower roses are often irrigated with moderately saline irrigation water. The salt/ballast ions are either present initially in poor quality raw water or reclaimed municipal water, or accumulated in greenhouse irrigation water that is captured and reused. Such ions can inhibit root absorption of essential nutrients. The objective of this work was to quantify the influence of NaCl concentration on the uptake of nitrate and potassium by roses and develop a predictive model of uptake inhibition based on NaCl, NO3 ?, and K+ concentration. One year-old rose plants (Rosa spp. ‘Kardinal’ on ‘Natal Briar’ rootstock) were moved into growth chambers where nitrogen and potassium depletion were monitored during 6 days. Eight different initial NaCl treatments varying from zero to 65 mol m?3 were used and within these there were two initial NO3 ? and K+ concentrations: high concentration (HC, 7.0 mol m?3 and 2.6 mol m?3 NO3 ? and K+ respectively) or low concentration (LC, 3.5 mol m?3 and 1.3 mol m?3 NO3 ? and K+ respectively). Plant NO3 ? uptake was negatively affected by NaCl concentration. NO3 ? maximum influx (Imax) declined from 5.1 µmol to 2.5 µmol per gram of plant dry weight per hour as NaCl concentration increased from zero to 65 mol m?3. A modified Michaelis–Menten (M–M) equation taking into account inhibition by NaCl provided the best fit for NO3 ? uptake in response to varying NaCl concentration. K+ uptake was unaffected by NaCl concentration. A M–M equation that did not include inhibition was suitable for describing K+ uptake at varying NaCl concentration. The resulting empirical models could assist with decision making, such as: adjustment of NO3 ? fertilization based on NaCl concentration, necessity of water desalinization, or determination of the desired leaching fraction. 相似文献
2.
Inorganic Carbon Limitation and Chemical Composition of Two Freshwater Green Microalgae 总被引:5,自引:1,他引:4
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Two freshwater chlorophytes, Chlorella vulgaris and Scenedesmus obliquus, were grown in inorganic carbon-limited continuous cultures in which HCO3− was the sole source of inorganic carbon. The response of the steady-state growth rate to the external total inorganic carbon concentration was reasonably well described by the Monod equation; however, the response to the internal nutrient concentration was only moderately well represented by the Droop equation when the internal carbon concentration was defined on a cellular basis. The Droop equation was totally inapplicable when total biomass (dry weight) was used to define internal carbon because the ratio of carbon to dry weight did not vary over the entire growth rate spectrum. In batch cultures, maximum growth rates were achieved at the CO2 levels present in atmospheric air and at HCO3− concentrations of 3 mM. No growth was observed at 100% CO2. Both nitrogen uptake and chlorophyll synthesis were tightly coupled to carbon assimilation, as indicated by the constant C/N and C/chlorophyll ratios found at all growth rates. The main influence of inorganic carbon limitation appears to be not on the chemical structure of the biomass, but rather on cell size; higher steady-state growth rates lead to bigger cells. 相似文献
3.
The effect of hydrogen peroxide (10?9–10?1 M) on the mycelial growth of the fungi Alternaria alternata, Cladosporium cladosporioides, Mucor hiemalis, and Paecilomyces lilacinus has been studied. The growth of fungi isolated from habitats with a background level of radioactive contamination was stopped by H2O2 concentrations equal to 10?3 and 10?2 M, whereas the growth of fungi that were isolated from habitats with high levels of radioactive contamination was only arrested by 10?1 M H2O2. The response of the different fungi to hydrogen peroxide was of three types: (1) a constant growth rate of fungal hyphae at H2O2 concentrations between 10?9 and 10?4 M and a decrease in this rate at 10?3 M H2O2, (2) a gradual decrease in the growth rate as the H2O2 concentration was increased, and (3) an increase in the growth rate as the H2O2 concentration was increased from 10?6 to 10?5 M. The melanin-containing species A. alternata and C. cladosporioides exhibited all three types of growth response to hydrogen peroxide, whereas the light-pigmented species M. hiemalis and P. lilacinus showed only the first type of growth response. A concentration of hydrogen peroxide equal to 10?1 M was found to be lethal to all of the fungi studied. The most resistant to hydrogen peroxide was found to be the strain A. alternata 56, isolated from the exclusion zone of the Chernobyl Nuclear Power Plant. 相似文献
4.
Two unicellular cyanobacteria Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942 showed contrasting responses to chromate stress with EC50 of 12 ± 2 and 150 ± 15 μM potassium dichromate respectively. There was no depletion of chromate in growth medium in both the cases. Using labeled chromate, very low accumulation (<1 nmol/108 cells) was observed in Synechocystis after incubation for 24 h in light. No accumulation of chromate could be observed in Synechococcus under these conditions. Chromate oxyanion is known to enter the cells using sulfate uptake channels. Therefore, inhibition of sulfate uptake caused by chromate was monitored using 35S labeled sulfate. IC50 values of chromate for 35sulfate uptake were higher in Synechococcus as compared to Synechocystis. The results suggested that the sulfate transporters in Synechococcus have lower affinity to chromate than those from Synechocystis possibly due to differences in affinity of sulfate receptors for chromate. Bioinformatic analyses revealed presence of sulfate and chromate transporters with considerable similarity; however, minor differences in these may play a role in their differential response to chromate. In both cases the IC50 values decreased when sulfate concentration was reduced in the medium indicating competitive inhibition of sulfate uptake by chromate. Interestingly, Synechococcus showed stimulation of growth at concentrations of chromate less than 100 μM, which affected its cell size without disturbing the ultrastructure and thylakoid organization. In Synechocystis, growth with 12 μM potassium dichromate damaged the ultrastructure and thylakoid organization with slight elongation of the cells. The results suggested that Synechococcus possesses efficient strategies to prevent entry and to remove chromate from the cell as compared to Synechocystis. This is the first time a differential response of Synechococcus 7942 and Synechocystis 6803 to chromate is reported. The contrasting characteristics observed in the two cyanobacteria will be useful in understanding the basis of resistance or susceptibility to chromate. 相似文献
5.
The influence of IAA in two concentrations (10−8M and 10−5M) on relations between growth, water absorption and cation uptake and accumulation was tested.IAA in a higher concentration retarded growth remarkably. First of all, potassium uptake and water absorption were significantly
decreased while the uptake of divalent cations was affected later and less remarkably. 10−8 M IAA accelerated the growth rate slightly together with acceleration of water absorption and cation uptake.
Presented at the International Symposium “Plant Growth Regulators” held on June 18 – 22, 1984 at Liblice, Czechoslovakia. 相似文献
6.
《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1986,889(2):225-235
Insulin (0.1 μM) and 1 μM epinephrine each increased the uptake and phosphorylation of 2-deoxyglucose by the perfused rat heart by increasing the apparent Vmax without altering the Km. Isoproterenol (10 μM), 50 μM methoxamine and 10 mM CaCl2 also increased uptake. Lowering of the perfusate Ca2+ concentration from 1.27 to 0.1 mM Ca2+, addition of the Ca2+ channel blocker nifedipine (1 μM) or addition of 1.7 mM EGTA decreased the basal rate of uptake of 2-deoxyglucose and prevented the stimulation due to 1 μM epinephrine. Stimulation of 2-deoxyglucose uptake by 0.1 μM insulin was only partly inhibited by Ca2+ omission, nifedipine or 1 mM EGTA. Half-maximal stimulation of 2-deoxyglucose uptake by insulin occurred at 2 nM and 0.4 nM for medium containing 1.27 and 0.1 mM Ca2+, respectively. Maximal concentrations of insulin (0.1 μM) and epinephrine (1 μM) were additive for glucose uptake and lactate output but were not additive for uptake of 2-deoxyglucose. Half-maximal stimulation of 2-deoxyglucose uptake by epinephrine occurred at 0.2 μM but maximal concentrations of epinephrine (e.g., 1 μM) gave lower rates of 2-deoxyglucose uptake than that attained by maximal concentrations of insulin. The addition of insulin increased uptake of 2-deoxyglucose at all concentrations of epinephrine but epinephrine only increased uptake at sub-maximal concentrations of insulin. The role of Ca2+ in signal reversal was also studied. Removal of 1 μM epinephrine after a 10 min exposure period resulted in a rapid return of contractility to basal values but the rate of 2-deoxyglucose uptake increased further and remained elevated at 20 min unless the Ca2+ concentration was lowered to 0.1 mM or nifedipine (1 μM) was added. Similarly, removal of 0.1 μM insulin after a 10 min exposure period did not affect the rate of 2-deoxyglucose uptake, which did not return to basal values within 20 min unless the concentration of Ca2+ was decreased to 0.1 mM. Insulin-mediated increase in 2-deoxyglucose uptake at 0.1 mM Ca2+ reversed upon hormone removal. It is concluded that catecholamines mediate a Ca2+-dependent increase in 2-deoxyglucose transport from either α or β receptors. Insulin has both a Ca2+-dependent and a Ca2+-independent component. Reversal studies suggest an additional role for Ca2+ in maintaining the activated transport state when activated by either epinephrine or insulin. 相似文献
7.
Free ribulose bisphosphate (RuBP4?) rather than its magnesium complex (RuBP-Mg2?) was the apparent substrate for spinach ribulose bisphosphate carboxylase/oxygenase. The apparent Km for total RuBP (pH 8.0 at 30° C) increased with increasing Mg2+ concentrations from 11.6 μM at 13.33 mM Mg2+ to 32.6 μM at 40.33 mM Mg2+. Similarly the apparent Km for RuBP-Mg2? complex increased with increasing Mg2+ from 9.4 μM at 13.33 mM Mg2+ to 29.7 μM at 40.33 mM Mg2+. However, the Km values for uncomplexed RuBP4? were independent of the (saturating) concentration of Mg2+ (Km=2.2 μM). The Vmax did not vary with the changing concentrations of Mg2+. In contrast, the Km for total RuBP remained constant with varying Mg2+ concentrations (Km=59.5 μM) for the enzyme from R. rubrum. The apparent Km for the RuBP-Mg2? complex decreased with increasing Mg2+ concentrations from 16.0 μM at 7.5 mM Mg2+ to 5.9 μM at 27.5 mM Mg2+. The initial velocity for the C. vinosum enzyme was also found to be independent of the (saturating) concentration of Mg2+ when total RuBP was varied in the assay. Thus the response to total RuBP by these two bacterial enzymes, which markedly differ in structure, was closely similar. 相似文献
8.
Uptake rates of nitrate and phosphate were measured for four species and one variety of Porphyra from Long Island Sound (USA) at two temperatures and two nutrient medium concentrations at increasing intervals over a 24- or 48-h period. Maximum uptake rates found were: V30 μM0-1 h=73.8 μmol NO3 g−1 DW h−1 and V3 μM0-1 h=16.7 μmol PO4 g−1 DW h−1, in the two thinnest Porphyra. We found that the nitrate uptake rates were significantly greater at 30 μM than 3 μM NO3 concentration, and that the uptake rates decreased with time of exposure. Temperature (5, 15, and 25 °C) did not have as strong an effect on nitrate uptake rates as did nutrient concentration. Q10 values and uptake rates at four different nitrate concentrations indicated that nutrient uptake at 5 °C was initially an active process. After 24 h, the processes involved appeared passive as Q10 values were between 1.0 and 1.3 and nitrate uptake curves were linear. Nitrate uptake rates correlated positively with the surface area/volume (SA/V) ratio. No coherent trends were found for uptake of phosphate, except that the uptake rates were significantly higher in 30 μM NO3 medium as opposed to 3 μM NO3. We did not find any significant difference in uptake rate and pattern between the summer species Porphyra purpurea (Roth.) C. Agardh, the eurythermic Porphyra suborbiculata Kjellm., the winter species Porphyra rosengurttii J. Coll and J. Cox, and the two varieties of Porphyra leucosticta Thur. Le Jol. (both winter species). 相似文献
9.
In potassium-limited chemostat cultures of Paracoccus denitrificans the maximum specific growth rate (µmax) was found to depend on the input potassium concentration: At 0.21mM µmax was 0.10–0.11 h-1; at 0.44 mM 0.15–0.16 h-1 and at 0.66 mM 0.20–0.21 h-1. The plots of the specific rates of oxygen-, succinate-and potassium consumption against gave straight lines. The intracellular potassium concentration was a linear function of and varied from 1% (0.13 M) at a value of 0.034 h-1 to 2.2% (0.29 M) at =0.26 h-1; the potassium concentration gradient and the potassium concentration in the culture fluid in the steady state were dependent on the input potassium concentration. The potassium concentration gradient varied from 8,900-1,200. At all values 20–25% of the total energy production was used for potassium transport. 350,100 and 30 ATP molecules were calculated to be required to maintain one potassium ion intracellular during 1 h at values of 0.034, 0.197 and 0.257 h-1 respectively. It is concluded that the amount of circulation of potassium is dependent on the potassium concentration gradient or on the potassium concentration in the culture in the steady state. The dependency of µmax on the input potassium concentration was explained by the assumption that at low input potassium concentrations the net uptake of potassium (influx-efflux) is not rapidly enough to maintain the high potassium gradient in the existing cells and to establish it in the newly formed cells. At high values and at high input potassium concentrations µmax is limited by the specific rate of oxygen consumption, which was found to be 11–12 mmol O2 g dry weight-1 h-1 at µmax for potassium-, succinate-and sulphate-limited chemostat cultures. 相似文献
10.
A. M. Zyakun V. V. Kochetkov B. P. Baskunov V. N. Zakharchenko V. P. Peshenko K. S. Laurinavichius T. O. Anokhina T. V. Siunova O. I. Sizova A. M. Boronin 《Microbiology》2013,82(3):280-289
By the example of glucose uptake by the soil bacteria Pseudomonas aureofaciens BS1393(pBS216) and Rhodococcus sp. 3–30 immobilized on a solid-phase surface (quartz sand), their growth parameters were determined: growth rate (doubling time), total CO2 production, CO2 production per cell, lag period with respect to substrate uptake, respiratory quotient. The growth of P. aureofaciens and Rhodococcus sp. on glucose revealed (1) differences of the lag period with respect to substrate (lag time of ~4 h for P. aureofaciens and ~26 h for Rhodococcus sp.); (2) differences between the maximal rates of CO2 production (~50 μg C-CO2 g?1 sand h?1 for P. aureofaciens and ~8.5 μg C-CO2 g?1 sand h?1 for Rhodococcus sp.); (3) differences in CO2 production per cell (~1.94 × 10?9 μM CO2/CFU for P. aureofaciens and more than ~3.4 × 10?9 μM CO2/CFU for Rhodococcus sp.). The kinetics of the metabolic CO2 isotopic composition was shown to be determined by the difference in the carbon isotopic characteristics of products in the cell. Upon introduction of glucose into the medium (the preparatory stage of the metabolism), the uptake of intracellular 13C-depleted products (lipids) is noted; at the stage of the maximal cell growth rate, introduced glucose is mainly metabolized; and at the final stage, upon exhaustion of substrate, the “stored” products—the lipid fraction—get involved in the metabolism. At the maximal rate of glucose uptake, the CO2 carbon isotopic fractionation coefficient relative to organic products of microbial biosynthesis was determined to be α = 1.009 ± 0.002. 相似文献
11.
Free ribulose hisphosphate (RuBP4?) rather than its magnesium complex (RuBP-Mg2?) was the apparent substrate for spinach ribulose bisphosphate carboxylase/oxygenase. The apparent Km for total RuBP (pH 8.0 at 30° C) increased with increasing Mg2+ concentrations from 11.6 μM at 13.33 mM Mg2+ to 32.6 μM at 40.33 mM Mg2+. Similarly the apparent Km for RuBP-Mg2? complex increased with increasing Mg2+ from 9.4 μM at 13.33 mM Mg2+ to 29.7 μM at 40.33 mM Mg2+. However, the Km values for uncomplexed RuBP4? were independent of the (saturating) concentration of Mg2+ (Km=2.2 μM). The Vmax did not vary with the changing concentrations of Mg2+. In contrast, the Km for total RuBP remained constant with varying Mg2+ concentrations (Km=59.5 μM) for the enzyme from R. rubrum. The apparent Km for the RuBP-Mg2? complex decreased with increasing Mg2+ concentrations from 16.0 μM at 7.5 mM Mg2+ to 5.9 μM at 27.5 mM Mg2+. The initial velocity for the C. vinosum enzyme was also found to be independent of the (saturating) concentration of Mg2+ when total RuBP was varied in the assay. Thus the response to total RuBP by these two bacterial enzymes, which markedly differ in structure, was closely similar. 相似文献
12.
Uptake of phosphate ions by 1 mm segments of isolated maize root cortex layers was studied. Cortex segments (from roots of 8 days old maize plants) absorb phosphate ions from 1 mM KH2PO4 in 0.2 mM CaSCO4 at the average rate of 34.3 ±3.2 μg Pi g?1 (fr. m.) h?1,i.e. 0.35± 0.02 μmol Pi g?1 (fr. m.) h?1. Phosphate uptake considerably increases after a certain period of “augmentation”,i.e. washing in aerated 0.2 mM CaSO4. This increase is completely blocked by the presence of 10 μg ml?1 cycloheximide. The relation of uptake rate to phosphate concentration in the medium was shown to have 3 phases in the concentration range of 0.02 - 40 mM. Transition points were found between 0.8–1 mM and 10–20 mM. Following Km and Vmax values were found: Km[mM] : 0.37 - 3.82 - 27.67 Vmax[μg Pi g?1 (fr. m.) h?1] : 3.33 - 39.40 - 66.67 We have found no sharp pH optimum for phosphate uptake. It proceeds at almost constant rate till pH 6.0 and then the uptake rate drops with increasing pH. At low phosphate concentrations (1 mM) the lowest uptake rate was found at 5 and 13 °C, while the uptake is higher at 5 °C than at 13 °C at phosphate concentrations higher than 1 mM. At these concentrations uptake rate at 35 °C is lower than at 25 °C. Phosphate uptake considerably decreased in anaerobic conditions. DNP and iodoacetate (0.1 mM) completely blocked phosphate uptake from 1 mM KH2PO4, while uptake from 5 and 10 mM KH2PO4 was left unaffected by these substances. The inhibitors of active - SH groups NEM and PCMB inhibited phosphate uptake: 10?3 M NEM by 81.6%, 104 M NEM by 42% and 10?4 M PCMB by 42%. 相似文献
13.
Atriplex halimus subsp. schweinfurthii is a newly found cadmium (Cd)-hyperaccumulator, but there have been no detailed studies on its physiological responses when Cd is hyperaccumulated. A. halimus was grown in hydroponic conditions to investigate the effect of cadmium chloride (CdCl2) on growth, water status, leaf chlorophyll concentration, proline and Cd accumulation. Treatments were prepared by adding 0, 50, 100, 200 and 400 μM CdCl2 to the nutrient medium. Plant growth was significantly affected at high-Cd treatments. Increased CdCl2 decreased chlorophyll concentration, transpiration and root hydraulic conductivity (L0). Hence water flux had only a little effect on the uptake of Cd in A. halimus seedlings. In contrast, proline content increased with increasing CdCl2 concentration. Plants accumulated substantial amount of Cd in different plant parts (shoot and root). Most of the Cd taken up was retained in roots (606.51 μg g−1DW after 15 d at 400 μM CdCl2). The addition of Cd in the culture medium affected calcium (Ca) and potassium (K) nutrition in both shoot and root. A. halimus provides a new plant resource for exploring the mechanism of Cd hyperaccumulation and has potential for use in the phytostabilization of Cd-contaminated salt soils. 相似文献
14.
Noradrenaline, a Transmitter Candidate in the Retina 总被引:5,自引:3,他引:2
N. N. Osborne 《Journal of neurochemistry》1981,36(1):17-27
The occurrence, metabolism, uptake, and release of noradrenaline were studied in the bovine retina with the following results. (1) Small amounts of noradrenaline occur in the retina and are restricted to the area corresponding to the inner nuclear and plexiform layers. (2) Retinal tissue can metabolise [14C]dopamine to form quantities of [14C]noradrenaline. (3) [14C]Noradrenaline can also be partly metabolised to form [14C]normetanephrine. (4) When bovine retinas were incubated with 5 × 10-7 M-[3H]noradrenaline for 20 min and processed for autoradiography, most of the label was associated with apparent nerve processes in the inner plexiform layer. Biochemical analysis showed that more than 95% of the label was noradrenaline. (5) [14C]Noradrenaline uptake saturated with increasing noradrenaline concentrations and followed Michaelis-Menten kinetics. This uptake could be accounted for by two processes, a high-affinity system with a Km1 of 5 × 10-8 M and a Vmax1 of 0.193 pmol/mg/10 min and a low-affinity system with a Km2 of 6.3 × 10-5 M and a Vmax2 of 0.109 nmol/mg/10 min. (6) Noradrenaline uptake was strongly dependent on temperature and sodium, less dependent on potassium, and independent of calcium and magnesium ions. (7) Centrally acting drugs, such as desipramine, imipramine, desmethylimipramine, and amitriptyline, inhibited noradrenaline uptake by more than 55% at the concentration of 5 × 10-5 M. These drugs at the same concentration diminished dopamine uptake by less than 30%. (8) Noradrenaline uptake is stereospecific, the (-) isomer having a greater affinity for the uptake sites than the (+) isomer. (9) [14C]Noradrenaline in the retina could be released by increasing the external potassium concentration. This release was calcium-dependent and was blocked by 20 mM-cobalt chloride. The present studies could be interpreted as supporting the idea that noradrenaline acts as a transmitter in the retina. 相似文献
15.
The effects of ouabain on the growth of murine lymphoblasts in vitro have been studied. Exposure of cells to ouabain (0.1 mM) initially inhibited 86Rb+ uptake rate, reduced the intracellular potassium concentration, and decreased population growth rates. Continued exposure to the same ouabain concentration resulted in an increase of 86Rb+ uptake rate, intracellular potassium content and population growth rates to control values (adaptation). When treated cells were resuspended in medium free of ouabain after 12 to 15 hours of ouabain treatment, 86Rb+ uptake rates and intracellular potassium levels exceeded those of untreated cells. Adaptation was inhibited by cycloheximide (3 μg/ml) and by actinomycin D (0.05 μg/ml). Kinetic analysis of transport suggested that while the total capacity of the Na+, K+ transport system increased, the affinity for both the cation (86Rb+) and ouabain decreased. 相似文献
16.
After propagation of Rhizopus javanicus in defined media containing glucose, urea, and mineral salts in deionized distilled water, the ability of the nonliving biomass to sequester cupric ion was assayed. Growth, uptake capacity (saturation uptake at >1 mM Cu2+ concentration in solution), and biosorptive yield (biomass concentration × uptake capacity) were increased by augmentation of the growth medium with mineral salts once growth was under way. In the stationary phase, the uptake capacity of mycelia, which were normally a poor biosorbent, was improved within 4 h of trace metal addition to the growth medium. Growth of the culture was inhibited by excessive concentrations (0.04 to 40 μM) of metals in the medium in the following order: Cu > Co ≥ Ni > Mn > Mo; zinc was not inhibitory at 40 μM, and chromium was stimulatory at 0.53 μM but slightly inhibitory at higher levels. Iron and potassium phosphate stimulated growth at levels of 0.53 and 40 mM, respectively. When R. javanicus was propagated in a medium with a high salt concentration, exponential growth (0.23 h−1) to a biomass concentration of >3 g/liter and a biosorptive yield of >500 μmol/liter was achieved. It is evident that the powerful biosorbent characteristics of Rhizopus biomass led to depletion of available trace minerals in suspension culture, which in turn limited growth. 相似文献
17.
《Journal of experimental marine biology and ecology》1982,62(3):211-224
NO−3 uptake rates were measured in situ for seven types of tissue of adult sporophytes of Macrocystis pyrifera (L.) C. Agardh. Uptake by mature blades of canopy fronds followed saturation kinetics. At near-saturation concentrations, mean rates of uptake by different tissues ranged from 0.1 to 2.1 μg-at.· g wet wt−1 · h−1 (7–68 ng-at. · cm−2· h−1). Different tissues incubated under similar environmental conditions took up NO−3 at different rates, indicating physiological differences. Uptake rates showed no apparent relation to tissue age or nutritional history, but were influenced by certain environmental factors: uptake was 44–48% slower in dark than at ambient mid-day light levels, and dark uptake was 40% slower by blades incubated at 12m depth than by blades incubated at the surface. These physiological and environmental differences resulted in generally rapid uptake by tissues located at or just below the surface and slower uptake by tissues deeper in the water column.Daily NO−3 uptake by M. pyrifera populations was predicted using a model based on in situ NO−3 uptake rates. According to predictions of the model, NO−3 concentrations of 1–2 μM throughout the water column are required to support kelp growth at the 4% · day−1 (wet wt) rate typical of inshore populations. Vertical stratification, with high NO−3 concentrations only at near-bottom depths, would result in severe nitrogen-limitation of growth. Seasonal changes in frond size distribution do not greatly affect nitrogen-limited growth rate. The model was also used to evaluate potential fertilizing methods and problems in management of offshore kelp farms. 相似文献
18.
Uncoupling of Methanogenesis from Growth of Methanosarcina barkeri by Phosphate Limitation 总被引:1,自引:0,他引:1
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David B. Archer 《Applied microbiology》1985,50(5):1233-1237
Production of methane by Methanosarcina barkeri from H2-CO2 was studied in fed-batch culture under phosphate-limiting conditions. A transition in the kinetics of methanogenesis from an exponentially increasing rate to a constant rate was due to depletion of phosphate from the medium. The period of exponentially increasing rate of methanogenesis was extended by increasing the initial concentration of phosphate in the medium. Addition of phosphate during the constant period changed the kinetics to an exponentially increasing rate of methanogenesis, indicating the reversibility of phosphate depletion. The relation between methanogenesis and growth of M. barkeri was investigated by measuring the incorporation of phosphorus, supplied as KH232PO4, in the medium. At a low (1 μM) initial concentration of phosphate in the medium and during the constant period of methanogenesis, there was no net cell growth. At a higher (10 μM) initial concentration of phosphate, cell growth proceeded linearly with time after phosphate had been removed from the medium by uptake into cells. 相似文献
19.
《Comparative biochemistry and physiology. C: Comparative pharmacology》1981,68(2):215-221
1. Lineweaver-Burk plots revealed the presence of two uptake mechanisms for serotonin, dopamine and norepinephrine. The high affinity uptake processes were found to have Km1 values of 0.281, 2.68 and 3.17 × 10−6 M and Vmax1 values of 0.154, 1.048 and 0.165 nmol/g/min for serotonin, dopamine and norepinerphine, respectively.2. At low biogenic amine concentrations uptake1 contributes more than uptake2 to the total amount of amine accumulated, as determined by the Michaelis-Menten equation, whereas at higher concentrations the reverse is true.3. 3-Chlorimiprimine was the most potent and select agent found for inhibiting serotonin uptake (ID50 value 0.5 × 10−6 M). The same is true of benztropine for inhibiting dopamine uptake (ID50 value 0.2 × 10−6 M).4. DALA (D-ala2-met-enkephalinamide) and morphine were found to be inhibitors of monoamine uptake within the concentration range 100–140 μM.5. The high affinity uptake mechanisms were found to be highly sensitive to Na+ omissions from the incubation medium.6. The monoamines were found to affect each other's uptake. These results suggest the existence of intraganglionic regulatory mechanisms involving neurotransmitter interrelationships. 相似文献
20.
Effects of N source and media-N and P levels were examined on growth, N uptake, and N2 fixation ofAzolla pinnata withAnabaena azollae association (azolla) at two inoculum-P concentrations. Each expeiment was conducted for 7 days in a growth chamber using azolla at a predetermined inoculum-P concentration and the growth media containing a combination of four levels of P (0, 15, 75, and 200 M) and three levels (0, 1, and 5 mM) of either15N-enriched NH
4
+
as ammonium sulfate or15N-enriched NO
3
–
as potassium nitrate. Nitrogen uptake and N2 fixation were measured by15N isotopic dilution method. Tissue P and N, N uptake, and N2-fixation increased with increasing P concentration in the media regardless of the inoculum-P level of azolla. Increasing P concentration in the media increased growth of azolla at low inoculum P, but the effect on high inoculum-P azolla was either small or absen. High inoculum-P concentration resulted in increased growth, tissue-N and P concentrations, N uptake, and N2 fixation by azolla. Ammonium in the growth media caused larger increase in tissue-N and greater repression of N2 fixation than equimolar concentration of NO
3
–
. In the presence of NH
4
+
or NO
3
–
, in the growth media, N uptake by azolla exceeded the corresponding decrease in N2 fixation, resulting in an overall increase in tissue-N concentration. Phosphorus in the media tended to negate the inhibitory effect of NH
4
+
or NO
3
–
on N2 fixation. A multiple regression model showed that the effect of tissue-N on N2 fixation was negative while that of tissue-P was positive. Therefore, a relative change in tissue-N and P appeared to regulate N2 fixation. Tissue-N and P had similar effects on relative growth rate of azolla also. Inoculum-P level of azolla was important in determining the response to media-P.This research was supported by a grant from USAID under Indo-US Science and Technology Initiative. 相似文献