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1.
Synthesis of stress proteins after heat shock and different periods of UV-B radiation were investigated with marine diatom species from the North Sea Ditylum brightwellii, Lithodesmium variabile, Odontella sinensis, Thalassiosira rotula and the Antarctic diatom Odontella weissfloggii from the Weddell Sea. Algae were grown in an artifical sea-water medium under controlled laboratory conditions: light/dark regime of 12:12 h (7.2 W m?2), normal air (0.035 vol.% CO2) and 18° or 4 °C. All the tested diatom species can produce heat shock proteins (HSPS) of the 70 kDa family by in vivo labelling with [35S]-methionine. The same results were obtained for Odontella sinensis, Ditylum brightwellii and Odontella weissflogii by estimation of the in vitro translation products with poly-A-mRNA isolated from these organisms. However, Odontella weissflogii, a species relatively insensitive to UV-B irradiance, did not synthesize UV-induced HSPS, whereas the UV-sensitive diatom Odontella sinensis, as well as Lithodesmium variabile, produced all the observed HSPS after UV-B exposure. In addition, a protein of 43 kDa was found after UV-B irradiance of the temperate Odontella sinensis. The temperate marine diatom Thalassiosira rotula synthesized 70 kDa and 5 7 kDa proteins after a heat shock and a UV-B exposure of 2 h, but a 40 kDa protein could not be detected, whereas a 60 kDa protein was found after 2 h UV-B exposure. The results are discussed in view of a possible adaptation of O. weissflogii to an enhanced UV dose. 相似文献
2.
P. J. APARICIO F. G. WITT J. M. RAMÍREZ M. A. QUIÑONES T. BALANDÍN 《Plant, cell & environment》1994,17(12):1323-1330
In M. braunii, the uptake of NO3− and NO2− is blue-light-dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO2-free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO3− and NO2− reductases were active, the pH increased to values of around 10, since the NH4+ generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H2SO4 of NO3− or NO2− uptake and reduction showed that two protons were consumed for every one NH4+ released. The uptake of Cl− was also triggered by blue light with a similar 10 s time response. However, the Cl− -dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl−) taken up by the cells were released to the medium. When the cells lacked NO3− and NO2− reductases, the shape of the alkalinization traces in the presence of NO3− and NO2− was similar to that in the presence of Cl−, suggesting that NO3− or NO2− was also released to the medium. Both the NO3− and Cl−-dependent rates of alkalinization were independent of mono- and divalent cations. 相似文献
3.
Segregation of nitrogen use between ammonium and nitrate of ectomycorrhizas and beech trees
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Martin Leberecht Michael Dannenmann Javier Tejedor Judy Simon Heinz Rennenberg Andrea Polle 《Plant, cell & environment》2016,39(12):2691-2700
Here, we characterized nitrogen (N) uptake of beech (Fagus sylvatica) and their associated ectomycorrhizal (EM) communities from NH4+ and NO3?. We hypothesized that a proportional fraction of ectomycorrhizal N uptake is transferred to the host, thereby resulting in the same uptake patterns of plants and their associated mycorrhizal communities. 15N uptake was studied under various field conditions after short‐term and long‐term exposure to a pulse of equimolar NH4+ and NO3? concentrations, where one compound was replaced by 15N. In native EM assemblages, long‐term and short‐term 15N uptake from NH4+ was higher than that from NO3?, regardless of season, water availability and site exposure, whereas in beech long‐term 15N uptake from NO3? was higher than that from NH4+. The transfer rates from the EM to beech were lower for 15N from NH4+ than from NO3?. 15N content in EM was correlated with 15N uptake of the host for 15NH4+, but not for 15NO3?‐derived N. These findings suggest stronger control of the EM assemblage on N provision to the host from NH4+ than from NO3?. Different host and EM accumulation patterns for inorganic N will result in complementary resource use, which might be advantageous in forest ecosystems with limited N availability. 相似文献
4.
Effects of ambient solar UV radiation in the field and of artifical UV irradiation under controlled laboratory conditions were studied with natural phytoplankton populations from Helgoland, German Bight, North Sea. The pattern of pigments varied after UV-A or UV-B plus a low dose of UV-A radiation: UV-A usually induced a stimulation of pigment biosynthesis; whereas UV-B plus UV-A led to a reduction of the contents of chlorophyll a, diadinoxanthin, fucoxanthin, peridinin and an unknown carotenoid; content of diatoxanthin was significantly enhanced. The damaging effect on nitrogen assimilation by UV was more pronounced after artificial UV-B plus UV-A irradiance compared to the influence of ambient solar UV under field conditions. The uptake of inorganic nitrogen was dependent on the dose and exposure time of UV radiation as well as on the species composition. The uptake of 15N-nitrate by natural phytoplankton collected in spring was more sensitive to UV irradiation than the assimilation of 15N-ammonium. UV-A radiation with a small part of shorter wavelengths at 315 nm (Philips-lamps in conjunction with the cut-off filter WG 320) caused a reduction of up to 12% whereas a stimulation of the 15NH4+ uptake was observed after exposure to UV-A without any UV-B (Philips lamps TL 60W/09N). Pattern of 15N-incorporation into free amino acids and pool sizes varied in dependence on the applied nitrogen compound and on the irradiation conditions. The impact of UV radiation on the pattern of 15N-Iabelled free amino acids and the pool sizes was different. 15N enrichment into all the tested amino acids was reduced after 5 h UV-B plus UV-A exposure and after application of 15NH4+. A depression of the glutamate and glutamine pools was observed after addition of 15N-nitrate alone. Pools of all main amino acids from phytoplankton in summer 1993/94 were inhibited by UV irradiance. Results are discussed with reference to the UV target (e.g. enzymes, pigments) and the adaptation to the environmental conditions. 相似文献
5.
The relative influence of the photoperiod and of periodic ammonium pulses in entraining the cell division cycle in nitrogen-limited cyclostat cultures differs dramatically in Hymenomonas carterae Braarud and Fagerl, Amphidinium carteri Hulburt and Thalassiosira weissflogii Grun. We examined how each species processes an NH4+ pulse at various times during the cell cycle and the L/D cycle. Rates of NH4+ uptake and changes in cellular concentrations of NH4+, free amino acids, and protein were examined after the addition of an NH4+ pulse. Depletion of NH4+ from the medium occurred earlier when the pulse was given at the beginning of the light period than at the beginning of the dark period in H. carterae and A. carteri. Depletion took longer in the T. weissflogii cultures and the kinetics were similar during both stages of the photocycle in this species. Similarly, the temporal phasing and maximum pool sizes varied with timing of the NH4+ pulse in H. carterae and A. carteri but complete assimilation was relatively rapid. More persistent pools of NH4+ and free amino acids accumulated in T. weissflogii, and the patterns of assimilation varied little as a function of the timing of the pulse with respect to the photocycle. Although nitrogen metabolism occurred rapidly in nitrogen-limited H. carterae and A. carteri, the entrainment of the cell division cycle by the photoperiod resulted in a large degree of uncoupling between completion of nitrogen assimilation and cell division. It is hypothesized that the strong entrainment of the cell division cycle of T. weissflogii by NH4+ pulses results from a relatively slow rate of nitrogen metabolism. 相似文献
6.
Gert Arnold 《Plant and Soil》1992,142(1):41-51
Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH4/NO3 uptake ratio and proton efflux. N was supplied in three NH4-N/NO3-N ratios, 3:1, 1:1 and 1:3, either as 15NH4+14NO3 or as 14NH4+15NO3. Total N and 15N acquisition of different plant parts were measured. Averaged over the whole tree, the NH4/NO3 uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively.
The excess cation-over-anion uptake value (Ca-Aa) appeared to be linearly related to the natural logarithm of the NH4/NO3 uptake ratio. Further, this uptake ratio was related to the NH4/NO3 ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern
as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause
soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers. 相似文献
7.
Miguel A. Quiñones Aurora Galván Emilio Fernández & Pedro J. Aparicio 《Plant, cell & environment》1999,22(9):1169-1175
The blue-light requirement for the biosynthesis of nitrite reductase and an NO2– transport system was studied in Chlamydomonas reinhardtii mutant S10. The only oxidized nitrogen species that could be taken up by this mutant was NO2–, due to the presence of NO2– transport systems and the absence of high-affinity NO3– transporters. NH4+-grown cells required illumination with blue light to recover the ability to take up NO2– when resuspended in an NO2–-containing NH4+-deprived medium. This blue-light- dependent recovery, which took 1 h, could be suppressed by cycloheximide, indicating that protein biosynthesis was involved. The biosynthesis of nitrite reductase took place in cell suspensions irradiated with red light, even in the absence of NO2–, thus suggesting that the process requiring blue light was the biosynthesis of an NO2– transport system. Nitrite reductase-containing cells (pre-irradiated with red light) took 1 h to start consuming NO2– when they were additionally irradiated with blue light in the presence of this anion, and this process was also cycloheximide-sensitive. The NO2– transport system operated either under red plus blue light or red light only. Thus, in C. reinhardtii mutant S10 cells, blue light was only required for the biosynthesis of an NO2– transport system and not for its activity. 相似文献
8.
B. J. Atwell 《Plant and Soil》1992,139(2):247-251
Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing NO3
-, NH4
+ or NH4NO3 with a total nitrogen concentration of 2.8 M m-3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO3
-, NH4
+ or NH4NO3. However, when NO3
- was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied with 15NH4NO3 or NH4
15NO3 for 30 h, NH4
+ uptake was generally twice as fast as NO3
- uptake, even for plants grown in the presence of NO3
-. Low rates of NO3
- uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO3
-. It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH4
+ and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH4
+ was the sole nitrogen source. 相似文献
9.
The complex interplay between photosynthesis and the uptake of nitrogen was investigated in samples from five lakes of different size and trophic state. When enriched with 15NH4+, the photosynthetic rate was often reduced for 4–5 h in samples believed to be nitrogen deficient. This implies that energy was reallocated from photosynthesis to the uptake and assimilation of N. Stimulation in C uptake at low levels of NH4+ enrichment was followed by a progressive decline with further NH4+ enrichment. On other occasions when ambient NH4+ was undetectable, nutrient regeneration by zooplankton supplied a significant fraction of the required nitrogen. At these times and when the plankton had sufficient available N, there usually was no change in photosynthetic rate with either NH4+ or NO3?enrichment. Typically, little NO3? was taken up and no photosynthetic response was observed. On two occasions, however, the uptake of NO3? was significant due to high NO3? and low NH4+ levels early in the season. At one of these times there was a reduction in photosynthesis with NO3? enrichment. A further complication was observed when photosynthesis decreased with NH4+ enrichment but increased with NO3? enrichment despite negligible NO3? uptake. These observations illustrate that the complex metabolism of these two nitrogen sources is not fully understood. At optimum light intensity, C:N uptake ratios, even under NH4+ enrichment, are only sufficient to maintain the cellular C:N ratio unless much of the fixed C is respired or excreted. Three observations suggest that photosynthesis and N uptake are not coupled, (i) Photoinhibition of C uptake, but not N uptake was observed when low light adapted populations are exposed to high light conditions, (ii) The light intensity for maximum N uptake was slightly less than that for carbon. (iii) Dark N uptake was always near 50% of the maximum rate in the light whereas the C uptake was near 2% of Popt. Certainly, there is an interconnection because dark C uptake was enhanced by NH4+ enrichment. 相似文献
10.
Jerry A. Topinka Bigelow 《Journal of phycology》1978,14(3):241-247
Ammoniun, nitrate and nitrite update by Fucus spiralis L. from the Massachusetts coast was examined. Uptake of all appeared to follow saturation type nutrient uptake kinetics, with uptake often restricted at ambient nutrient concentrations. Although only relatively large difference in K8 values could be easily distinguished, K8 values for NO3? and NH4+ were generally similar and low compared with NO2?. There was also some suggestion that K8 was reduced at lower temperatures. At 15 C. Vmax for light and dark uptake for both NH4+ and NO3?, and light uptake of N02? were similar, suggesting comparable potential use at higher concentrations. Ammonium and NO3?uptake decreased at lower temperatures giving Qro values of 1.8 and 1.6, respectively, between 5 and 15°C. Nitrate and NH4+ were taken up together and high levels of NH4+ did not inhibit NO3? uptake. Light did not affect uptake of either but did stimulate NO2? uptake. Ammonium and NO3? uptake were highest in apical frond and whole young plants, and lowest in slower growing, older frond and stipe. On a relative basis. NO3?, NH4+ and NO2? were estimated to have contributed ca. 59, 39 and 2% respectively, to the yearly N uptake by apical frond. During winter, NO3? would provide ca. twice the N to F. spiralis as would, NH4+. From summer to early fall, when NO3? levels are lower, NO3? and NH4+ would be used in comparable amounts. 相似文献
11.
Release and uptake of NO was measured in a slightly alkaline (pH 7.8) and an acidic (pH 4.7) cambisol. In the alkaline soil under aerobic conditions, NO release was stimulated by ammonium and inhibited by nitrapyrin. Nitrate accumulated simultaneously and was also inhibited by nitrapyrin.15NO was released after fertilization with15NH4NO3 but not with NH4
15NO3. The results indicate that in aerobic alkaline cambisol NO was mainly produced during nitrification of ammonium. The results were different under anaerobic conditions and also in the acidic cambisol. There, NO release was stimulated by nitrate and not by ammonium, and was inhibited by chlorate and not by nitrapyrin indicating that NO production was exclusively due to reduction of nitrate. The results were confirmed by15NO being released mainly from NH4
15NO3 rather than from15NH4NO3. The observed patterns of NO release were explained by the NO production processes being stimulated by either ammonium or nitrate in the two different soils, whereas the NO consumption processes being only stimulated by nitrate. NO release was larger than N2O release, but both were small compared to changes in concentrations of soil ammonium or nitrate.(*request for offprints) 相似文献
12.
In Vivo Blue-Light Activation of Chlamydomonas reinhardii Nitrate Reductase 总被引:29,自引:14,他引:15
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Chlamydomonas reinhardii cells, growing photoautotrophically under air, excreted to the culture medium much higher amounts of NO2− and NH4+ under blue than under red light. Under similar conditions, but with NO2− as the only nitrogen source, the cells consumed NO2− and excreted NH4+ at similar rates under blue and red light. In the presence of NO3− and air with 2% CO2 (v/v), no excretion of NO2− and NH4+ occurred and, moreover, if the bubbling air of the cells that were currently excreting NO2− and NH4+ was enriched with 2% CO2 (v/v), the previously excreted reduced nitrogen ions were rapidly reassimilated. The levels of total nitrate reductase and active nitrate reductase increased several times in the blue-light-irradiated cells growing on NO3− under air. When tungstate replaced molybdate in the medium (conditions that do not allow the formation of functional nitrate reductase), blue light activated most of the preformed inactive enzyme of the cells. Furthermore, nitrate reductase extracted from the cells in its inactive form was readily activated in vitro by blue light. It appears that under high irradiance (90 w m−2) and low CO2 tensions, cells growing on NO3− or NO2− may not have sufficient carbon skeletons to incorporate all the photogenerated NH4+. Because these cells should have high levels of reducing power, they might use NO3− or, in its absence, NO2− as terminal electron acceptors. The excretion of the products of NO2− and NH4+ to the medium may provide a mechanism to control reductant level in the cells. Blue light is suggested as an important regulatory factor of this photorespiratory consumption of NO3− and possibly of the whole nitrogen metabolism in green algae. 相似文献
13.
Characterization of ammonium and nitrate uptake and assimilation in roots of tea plants 总被引:3,自引:0,他引:3
Y. Y. Yang X. H. Li R. G. Ratcliffe J. Y. Ruan 《Russian Journal of Plant Physiology》2013,60(1):91-99
It has been pointed out that tea (Camellia sinensis (L.) O. Kuntze) prefers ammonium (NH 4 + ) over nitrate (NO 3 ? ) as an inorganic nitrogen (N) source. 15N studies were conducted using hydroponically grown tea plants to clarify the characteristics of uptake and assimilation of NH 4 + and NO 3 ? by tea roots. The total 15N was detected, and kinetic parameters were calculated after feeding 15NH 4 + or 15NO 3 ? to tea plants. The process of N assimilation was studied by monitoring the dynamic 15N abundance in the free amino acids of tea plant roots by GC-MS. Tea plants supplied with 15NH 4 + absorbed significantly more 15N than those supplied with 15NO 3 ? . The kinetics of 15NH 4 + and 15NO 3 ? influx into tea plants followed a classic biphasic pattern, demonstrating the action of a high affinity transport system (HATS) and a low affinity transport system (LATS). The V max value for NH 4 + uptake was 54.5 nmol/(g dry wt min), which was higher than that observed for NO 3 ? (39.3 nmol/(g dry wt min)). KM estimates were approximately 0.06 mM for NH 4 + and 0.16 mM for NO 3 ? , indicating a higher rate of NH 4 + absorption by tea plant roots. Tea plants fed with 15NH 4 + accumulated larger amounts of assimilated N, especially glutamine (Gln), compared with those fed with 15NO 3 ? . Gln, Glu, theanine (Thea), Ser, and Asp were the main free amino acids that were labeled with 15N under both conditions. The rate of N assimilation into Thea in the roots of NO 3 ? -supplied tea plants was quicker than in NH 4 + -supplied tea plants. NO 3 ? uptake by roots, rather than reduction or transport within the plant, seems to be the main factor limiting the growth of tea plants supplied with NO 3 ? as the sole N source. The NH 4 + absorbed by tea plants directly, as well as that produced by NO 3 ? reduction, was assimilated through the glutamine synthetase-glutamine oxoglutarate aminotransferase pathway in tea plant roots. The 15N labeling experiments showed that there was no direct relationship between the Thea synthesis and the preference of tea plants for NH 4 + . 相似文献
14.
Effect of oxygen deficiency on nitrogen assimilation and amino acid metabolism of soybean root segments 总被引:1,自引:0,他引:1
Plants submitted to O2 deficiency present a series of biochemical modifications, affecting overall root metabolism. Here, the effect of hypoxia on the metabolic fate of 15N derived from 15NO3 ?, 15NO2 ? and 15NH4 + in isolated soybean root segments was followed by gas chromatography–mass spectrometry, to provide a detailed analysis of nitrogen assimilation and amino acid biosynthesis under hypoxia. O2 deficiency decreased the uptake of the nitrogen sources from the solution, as ratified by the lower 15NO3 ? and 15NH4 + enrichment in the root segments. Moreover, analysis of endogenous NO2 ? and 15NH4 + levels suggested a slower metabolism of these ions under hypoxia. Accordingly, regardless of the nitrogen source, hypoxia reduced total 15N incorporation into amino acids. Analysis of 15N enrichment patterns and amino acid levels suggest a redirecting of amino acid metabolism to alanine and γ-aminobutyric acid synthesis under hypoxia and a differential sensitivity of individual amino acid pathways to this stress. Moreover, the role of glutamine synthetase in nitrogen assimilation both under normoxia and hypoxia was ratified. In comparison with 15NH4 +, 15NO2 ? assimilation into amino acids was more strongly affected by hypoxia and NO2 ? accumulated in root segments during this stress, indicating that nitrite reductase may be an additional limiting step. NO2 ? accumulation was associated with a higher nitric oxide emission. 15NO3 ? led to much lower 15N incorporation in both O2 conditions, probably due to the limited nitrate reductase activity of the root segments. Overall, the present work shows that profound alterations of root nitrogen metabolism occur during hypoxic stress. 相似文献
15.
The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH4NO3 and pre-treated by extending the 11 h photosynthetically significant light period either by 1 h (short-day or SD plants) or 7 h (long-day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, 15N-labelled NH4+ or NH4++ NO3? was supplied over a 20-day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO3? reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO3? uptake restarting 1 or 2 days earlier than NH4+ uptake, even when NH4+ was the only form of N supply. LD timothy plants supplied solely with NH4+ were slowest to resume uptake of mineral N. Supplying NO3? in addition to NH4+ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short-term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink-driven rates of N remobilization and their interactions with mineral N uptake following defoliation. 相似文献
16.
Tomato growth was examined in solution culture under constant pH and low levels of NH4+ or NO3?. There were five nitrogen treatments: 20 mmoles m?3 NH4+, 50 mmoles m?3 NO3?, 100 mmoles m?3 NH4+ 200 mmoles m?3 NO3?, and 20 mmoles m?3 NH4++ 50 mmoles m?3 NO3?. The lower concentrations (20 mmoles m?3 NH4+ and 50 mmoles m?3 NO3?) were near the apparent Km for net NH4+ and NO3? uptake; the higher concentrations (100 mmoles m?3 NH4+ and 200 mmoles m?3 NO3?) were near levels at which the net uptake of NH4+ or NO3? saturate. Although organic nitrogen contents for the higher NO3? and the NH4++ NO3? treatments were 22.2–30.3% greater than those for the lower NO3? treatment, relative growth rates were initially only 10–15% faster. After 24 d, relative growth rates were similar among those treatments. These results indicate that growth may be only slightly nitrogen limited when NH4+ or NO3? concentrations are held constant over the root surface at near the apparent Km concentration. Relative growth rates for the two NH4+ treatments were much higher than have been previously reported for tomatoes growing with NH4+ as the sole nitrogen source. Initial growth rates under NH4+ nutrition did not differ significantly (P≥ 0.05) from those under NO3? or under combined NH4++ NO3?. Growth rates slowed after 10–15 d for the NH4+ treatments, whereas they remained more constant for the NO3? and mixed NH4++ NO3? treatments over the entire observation period of 24–33 d. The decline in growth rate under NH4+ nutrition may have resulted from a reduction in Ca2+, K+, and/or Mg2+ absorption. 相似文献
17.
The uptake of nitrate, nitrite and ammonium by Codium fragile subsp. tomentosoides (van Goor) Silva was measured at different combinations of temperature (6–30 C) and irradiance (0–140 μEin.m-2. s-1). Uptake of all three forms of N was greater at 12–24 C than at 6 and 30 C. Although uptake was stimulated by light, saturation occurred at relatively low irradiance (7–28 μEin m-2 s-1, depending on the N source and temperature). The Michaelis-Menten uptake constants (Vmax K)varied with temperature. Vmax was greatest at intermediate temperatures and K was lowest at lower temperatures. The Vmaxfor NH4+ was higher and the K, for NH4+was lower than those for NO3-- and NO2--. Codium was capable of simultaneously taking up all three forms of inorganic N although the presence of NH4+ reduced the uptake of both NO3-- and NO2--. The results of this study indicate that part of the ecological success of Codium in a N-limited environment may be due to its N uptake capabilities. 相似文献
18.
NH4+ and NO3? uptake were measured by continuous sampling with an autoanalyzer. For Hypnea musciformis (Wulfen) Lamouroux, NO3?up take followed saturable kinetics (K2=4.9 μg-at N t?1, Vmax= 2.85 μg- at N, g(wet)?1. h?1. The ammonium uptake data fit a trucatd hyperbola, i.e., saturation was not reach at the concentrations used. NO3? uptake was reduced one-half in the presence of NH4+, but presence of NO3? had no effect on NH4+ uptake. Darkness reduced both NO3? and NH4+ uptake by one-third to one-half. For Macrocystis pyrufera (L) C. Agardh, NO3? uptake followed saturable kinetices: K2=13.1 μg-at N. l?1. Vmax=3.05 μg-at N. g(wet)?1. h?1.NH4+ uptake showed saturable kinetics at concentration below 22 μg-at N l -1 (K2=5.3 μg-at N.1–1, Vmax= 2.38 μg-at N G (wet)?1.h?1: at higher concentration uptake increased lincarly with concentrations. NO3?and NH4+ were taken up simulataneously: presence of one form did not affect uptake of the other. 相似文献
19.
Louise M. Nelson 《Plant and Soil》1987,98(2):275-284
Summary This study was conducted to determine the effect of short term application of NH4NO3 on nodule function and to determine whether the rhizobial isolate used was a significant factor in this effect. Pea plants
were inoculated with 10 differentRhizobium leguminosarum isolates and grown for 3 weeks in N-free medium before addition of 0, 1, 2 or 5 mM NH4NO3 for 2 to 7 days. Acetylene reduction and leghemoglobin content decreased with increasing exposure time to NH4NO3 and with increasing concentration of NH4NO3. NH
4
+
and NO
3
−
depletion from the nutrient medium were assayed in plants exposed to 5 mM NH4NO3 and mean uptake rates were similar for each ion. There were significant differences among isolates in the rate of decrease
of C2H2 reduction with increasing NH4NO3 concentration (C2H2 reduction responsiveness to NH4NO3) 4 and 7 days after addition of NH4NO3 but no differences after 2 days of exposure to NH4NO3. There were significant differences among isolates in NH
4
+
depletion from the nutrient medium but these differences were not correlated with the differences observed in C2H2 reduction. Ranking of the isolates for C2H2 reduction responsiveness to NH4NO3 applied to plants with nodules was different from that obtained when NH4NO3 was applied at seeding. Isolates with varying sensitivity to NH4NO3 may be useful tools for determining the mechanisms responsible for inhibition of symbiotic N2 fixation by combined nitrogen.
NRCC paper no. 25863. 相似文献
20.
《Plant and Soil》2000,220(1-2):175-187
Several studies have previously shown that shoot removal of forage species, either by cutting or herbivore grazing, results
in a large decline in N uptake (60%) and/or N2 fixation (80%). The source of N used for initial shoot growth following defoliation relies mainly on mobilisation of N reserves
from tissues remaining after defoliation. To date, most studies investigating N-mobilisation have been conducted, with isolated
plants grown in controlled conditions. The objectives of this study were for Lolium perenne L., grown in a dense canopy in field conditions, to determine: 1) the contribution of N-mobilisation, NH4
+ uptake and NO3
- uptake to growing shoots after defoliation, and 2) the contribution of the high (HATS) and low (LATS) affinity transport
systems to the total plant uptake of NH4
+ and NO3
-. During the first seven days following defoliation, decreases in biomass and N-content of roots (34% and 47%, respectively)
and to a lesser extent stubble (18% and 43%, respectively) were observed, concomitant with mobilisation of N to shoots. The
proportion and origin of N used by shoots (derived from reserves or uptake) was similar to data reported for isolated plants.
Both HATS and LATS contributed to the total root uptake of NH4
+ and NO3
-. The Vmax of both the NH4
+ and NO3
- HATS increased as a function of time after defoliation, and both HATS systems were saturated by substrate concentrations
in the soil at all times. The capacity of the LATS was reduced as soil NO3
- and NH4
+ concentrations decreased following defoliation. Data from 15N uptake by field-grown plants, and uptake rates of NH4
+ and NO3
- estimated by excised root bioassays, were significantly correlated, though uptake was over-estimated by the later method.
The results are discussed in terms of putative mechanisms for regulating N uptake following severe defoliation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献