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1.
It has been hypothesized that under NO(3)(-) nutrition a high apoplastic pH in leaves depresses Fe(3+) reductase activity and thus the subsequent Fe(2+) transport across the plasmalemma, inducing Fe chlorosis. The apoplastic pH in young green leaves of sunflower (Helianthus annuus L.) was measured by fluorescence ratio after xylem sap infiltration. It was shown that NO(3)(-) nutrition significantly increased apoplastic pH at distinct interveinal sites (pH >/= 6.3) and was confined to about 10% of the whole interveinal leaf apoplast. These apoplastic pH increases presumably derive from NO(3)(-)/proton cotransport and are supposed to be related to growing cells of a young leaf; they were not found in the case of sole NH(4)(+) or NH(4)NO(3) nutrition. Complementary to pH measurements, the formation of Fe(2+)-ferrozine from Fe(3+)-citrate was monitored in the xylem apoplast of intact leaves in the presence of buffers at different xylem apoplastic pH by means of image analysis. This analysis revealed that Fe(3+) reduction increased with decreasing apoplastic pH, with the highest rates at around pH 5. 0. In analogy to the monitoring of Fe(3+) reduction in the leaf xylem, we suggest that under alkaline nutritional conditions at interveinal microsites of increased apoplastic pH, Fe(3+) reduction is depressed, inducing leaf chlorosis. The apoplastic pH in the xylem vessels remained low in the still-green veins of leaves with intercostal chlorosis. 相似文献
2.
The mechanism of iron (Fe) uptake from the leaf apoplast into leaf mesophyll cells was studied to evaluate the putative Fe
inactivation as a possible cause of Fe deficiency chlorosis. For this purpose, sunflower (Helianthus annuus L.) and faba bean
plants (Vicia faba L.) were precultured with varied Fe and bicarbonate (HCO
3
-
) supply in nutrient solution. After 2–3 weeks preculture, Fe III reduction and 59Fe uptake by leaf discs were measured in solutions with Fe supplied as citrate or synthetic chelates in darkness. The data
clearly indicate that Fe III reduction is a prerequisite for Fe uptake into leaf cells and that the Fe nutritional status of plants does not affect either
process. In addition, varied supply of Fe and HCO
3
-
to the root medium during preculture had no effect on pH of the xylem sap and leaf apoplastic fluid. A varied pH of the incubation
solution had no significant effect on Fe III reduction and Fe uptake by leaf discs in the physiologically relevant pH range of 5.0–6.0 as measured in the apoplastic leaf
fluid. It is concluded that Fe inactivation in the leaf apoplast is not a primary cause of Fe deficiency chlorosis induced
by bicarbonate.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
A recent study (D. C. Cooper, F. W. Picardal, A. Schimmelmann, and A. J. Coby, Appl. Environ. Microbiol. 69:3517-3525, 2003) has shown that NO 3− and NO 2− (NO x−) reduction by Shewanella putrefaciens 200 is inhibited in the presence of goethite. The hypothetical mechanism offered to explain this finding involved the formation of a Fe(III) (hydr)oxide coating on the cell via the surface-catalyzed, abiotic reaction between Fe 2+ and NO 2−. This coating could then inhibit reduction of NO x− by physically blocking transport into the cell. Although the data in the previous study were consistent with such an explanation, the hypothesis was largely speculative. In the current work, this hypothesis was tested and its environmental significance explored through a number of experiments. The inhibition of ~3 mM NO 3− reduction was observed during reduction of a variety of Fe(III) (hydr)oxides, including goethite, hematite, and an iron-bearing, natural sediment. Inhibition of oxygen and fumarate reduction was observed following treatment of cells with Fe 2+ and NO 2−, demonstrating that utilization of other soluble electron acceptors could also be inhibited. Previous adsorption of Fe 2+ onto Paracoccus denitrificans inhibited NO x− reduction, showing that Fe(II) can reduce rates of soluble electron acceptor utilization by non-iron-reducing bacteria. NO 2− was chemically reduced to N 2O by goethite or cell-sorbed Fe 2+, but not at appreciable rates by aqueous Fe 2+. Transmission and scanning electron microscopy showed an electron-dense, Fe-enriched coating on cells treated with Fe 2+ and NO 2−. The formation and effects of such coatings underscore the complexity of the biogeochemical reactions that occur in the subsurface. 相似文献
4.
The article describes factors and processes which lead to Fe chlorosis (lime chlorosis) in plants grown on calcareous soils. Such soils may contain high HCO 3
- concentrations in their soil solution, they are characterized by a high pH, and they rather tend to accumulate nitrate than ammonium because due to the high pH level ammonium nitrogen is rapidly nitrified and/or even may escape in form of volatile NH 3. Hence in these soils plant roots may be exposed to high nitrate and high bicarbonate concentrations. Both anion species are involved in the induction of Fe chlorosis.Physiological processes involved in Fe chlorosis occur in the roots and in the leaves. Even on calcareous soils and even in plants with chlorosis the Fe concentration in the roots is several times higher than the Fe concentration in the leaves. This shows that the Fe availability in the soil is not the critical process leading to chlorosis but rather the Fe uptake from the root apoplast into the cytosol of root cells. This situation applies to dicots as well as to monocots. Iron transport across the plasmamembrane is initiated by Fe III reduction brought about by a plasmalemma located Fe III reductase. Its activity is pH dependent and at alkaline pH supposed to be much depressed. Bicarbonate present in the root apoplast will neutralize the protons pumped out of the cytosol and together with nitrate which is taken up by a H +/nitrate cotransport high pH levels are provided which hamper or even block the Fe III reduction.Frequently chlorotic leaves have higher Fe concentrations than green ones which phenomenon shows that chlorosis on calcareous soils is not only related to Fe uptake by roots and Fe translocation from the roots to the upper plant parts but also dependent on the efficiency of Fe in the leaves. It is hypothesized that also in the leaves Fe III reduction and Fe uptake from the apoplast into the cytosol is affected by nitrate and bicarbonate in an analogous way as this is the case in the roots. This assumption was confirmed by the highly significant negative correlation between the leaf apoplast pH and the degree of iron chlorosis measured as leaf chlorophyll concentration. Depressing leaf apoplast pH by simply spraying chlorotic leaves with an acid led to a regreening of the leaves. 相似文献
5.
The K +-sensitive fluorescent dye benzofuran isophthalate (PBFI) and the pH-sensitive fluorescein isothiocyanate dextran (FITC-Dextran)
were used to investigate the influence of light/dark transitions on apoplastic pH and K + concentration in intact leaves of Vicia faba L. with fluorescence ratio imaging microscopy. Illumination by red light led to an acidification in the leaf apoplast due
to light-induced H + extrusion. Similar apoplastic pH responses were found on adaxial and abaxial sides of leaves after light/dark transition.
Stomatal opening resulted only in a slight pH decrease (0.2 units) in the leaf apoplast. Gradients of apoplastic pH exist
in the leaf apoplast, being about 0.5–1.0 units lower in the center of the xylem veins as compared with surrounding cells.
The apoplastic K + concentration in intact leaves declined during the light period. A steeper light-induced decrease in apoplastic K +, possibly caused by higher apoplastic K +, was found on the abaxial side of leaves concentration. Simultaneous measurements of apoplastic pH and K + demonstrated that a light-induced decline in apoplastic K + concentration indicative of net K + uptake into leaf cells occurs independent of apoplastic pH changes. It is suggested that the driving force that is generated
by H + extrusion into the leaf apoplast due to H +-ATPase activity is sufficient for passive K + influx into the leaf cells.
Received: 7 March 2000 / Accepted: 12 May 2000 相似文献
6.
The regulation of NO 3− assimilation by xylem flux of NO 3− was studied in illuminated excised leaves of soybean ( Glycine max L. Merr. cv Kingsoy). The supply of exogenous NO 3− at various concentrations via the transpiration stream indicated that the xylem flux of NO 3− was generally rate-limiting for NO 3− reduction. However, NO 3− assimilation rate was maintained within narrow limits as compared with the variations of the xylem flux of NO 3−. This was due to considerable remobilization and assimilation of previously stored endogenous NO 3− at low exogenous NO 3− delivery, and limitation of NO 3− reduction at high xylem flux of NO 3−, leading to a significant accumulation of exogenous NO 3−. The supply of 15NO 3− to the leaves via the xylem confirmed the labile nature of the NO 3− storage pool, since its half-time for exchange was close to 10 hours under steady state conditions. When the xylem flux of 15NO 3− increased, the proportion of the available NO 3− which was reduced decreased similarly from nearly 100% to less than 50% for both endogenous 14NO 3− and exogenous 15NO 3−. This supports the hypothesis that the assimilatory system does not distinguish between endogenous and exogenous NO 3− and that the limitation of NO 3− reduction affected equally the utilization of NO 3− from both sources. It is proposed that, in the soybean leaf, the NO 3− storage pool is particularly involved in the short-term control of NO 3− reduction. The dynamics of this pool results in a buffering of NO 3− reduction against the variations of the exogenous NO 3− delivery. 相似文献
7.
We examined nitrate-dependent Fe 2+ oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of “ Candidatus Brocadia sinica” anaerobically oxidized Fe 2+ and reduced NO 3− to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein −1 min −1, respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of “ Ca. Brocadia sinica” (10 to 75 nmol NH 4+ mg protein −1 min −1). A 15N tracer experiment demonstrated that coupling of nitrate-dependent Fe 2+ oxidation and the anammox reaction was responsible for producing nitrogen gas from NO 3− by “ Ca. Brocadia sinica.” The activities of nitrate-dependent Fe 2+ oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO 3− ± SD of “ Ca. Brocadia sinica” was determined to be 51 ± 21 μM. Nitrate-dependent Fe 2+ oxidation was further demonstrated by another anammox bacterium, “ Candidatus Scalindua sp.,” whose rates of Fe 2+ oxidation and NO 3− reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein −1 min −1, respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe 2+ oxidation and the anammox reaction decreased the molar ratios of consumed NO 2− to consumed NH 4+ (ΔNO 2−/ΔNH 4+) and produced NO 3− to consumed NH 4+ (ΔNO 3−/ΔNH 4+). These reactions are preferable to the application of anammox processes for wastewater treatment. 相似文献
8.
The redox cycle of 2,5-dimethoxybenzoquinone (2,5-DMBQ) is proposed as a source of reducing equivalent for the regeneration of Fe 2+ and H 2O 2 in brown rot fungal decay of wood. Oxalate has also been proposed to be the physiological iron reductant. We characterized the effect of pH and oxalate on the 2,5-DMBQ-driven Fenton chemistry and on Fe 3+ reduction and oxidation. Hydroxyl radical formation was assessed by lipid peroxidation. We found that hydroquinone (2,5-DMHQ) is very stable in the absence of iron at pH 2 to 4, the pH of degraded wood. 2,5-DMHQ readily reduces Fe 3+ at a rate constant of 4.5 × 10 3 M −1s −1 at pH 4.0. Fe 2+ is also very stable at a low pH. H 2O 2 generation results from the autoxidation of the semiquinone radical and was observed only when 2,5-DMHQ was incubated with Fe 3+. Consistent with this conclusion, lipid peroxidation occurred only in incubation mixtures containing both 2,5-DMHQ and Fe 3+. Catalase and hydroxyl radical scavengers were effective inhibitors of lipid peroxidation, whereas superoxide dismutase caused no inhibition. At a low concentration of oxalate (50 μM), ferric ion reduction and lipid peroxidation are enhanced. Thus, the enhancement of both ferric ion reduction and lipid peroxidation may be due to oxalate increasing the solubility of the ferric ion. Increasing the oxalate concentration such that the oxalate/ferric ion ratio favored formation of the 2:1 and 3:1 complexes resulted in inhibition of iron reduction and lipid peroxidation. Our results confirm that hydroxyl radical formation occurs via the 2,5-DMBQ redox cycle. 相似文献
9.
The present lab-scale research reveals the potential of implementation of an oxygen-limited autotrophic nitrification-denitrification (OLAND) system with normal nitrifying sludge as the biocatalyst for the removal of nitrogen from nitrogen-rich wastewater in one step. In a sequential batch reactor, synthetic wastewater containing 1 g of NH 4+-N liter −1 and minerals was treated. Oxygen supply to the reactor was double-controlled with a pH controller and a timer. At a volumetric loading rate ( Bv) of 0.13 g of NH 4+-N liter −1 day −1, about 22% of the fed NH 4+-N was converted to NO 2−-N or NO 3−-N, 38% remained as NH 4+-N, and the other 40% was removed mainly as N 2. The specific removal rate of nitrogen was on the order of 50 mg of N liter −1 day −1, corresponding to 16 mg of N g of volatile suspended solids −1 day −1. The microorganisms which catalyzed the OLAND process are assumed to be normal nitrifiers dominated by ammonium oxidizers. The loss of nitrogen in the OLAND system is presumed to occur via the oxidation of NH 4+ to N 2 with NO 2− as the electron acceptor. Hydroxylamine stimulated the removal of NH 4+ and NO 2−. Hydroxylamine oxidoreductase (HAO) or an HAO-related enzyme might be responsible for the loss of nitrogen. 相似文献
10.
Many reports have shown that plant growth and yield is superior on mixtures of NO 3− and NH 4+ compared with provision of either N source alone. Despite its clear practical importance, the nature of this N-source synergism at the cellular level is poorly understood. In the present study we have used the technique of compartmental analysis by efflux and the radiotracer 13N to measure cellular turnover kinetics, patterns of flux partitioning, and cytosolic pool sizes of both NO 3− and NH 4+ in seedling roots of rice ( Oryza sativa L. cv IR72), supplied simultaneously with the two N sources. We show that plasma membrane fluxes for NH 4+, cytosolic NH 4+ accumulation, and NH 4+ metabolism are enhanced by the presence of NO 3−, whereas NO 3− fluxes, accumulation, and metabolism are strongly repressed by NH 4+. However, net N acquisition and N translocation to the shoot with dual N-source provision are substantially larger than when NO 3− or NH 4+ is provided alone at identical N concentrations. 相似文献
11.
The role of NO 3− and NO 2− in the induction of nitrite reductase (NiR) activity in detached leaves of 8-day-old barley ( Hordeum vulgare L.) seedlings was investigated. Barley leaves contained 6 to 8 micromoles NO 2−/gram fresh weight × hour of endogenous NiR activity when grown in N-free solutions. Supply of both NO 2− and NO 3− induced the enzyme activity above the endogenous levels (5 and 10 times, respectively at 10 millimolar NO 2− and NO 3− over a 24 hour period). In NO 3−-supplied leaves, NiR induction occurred at an ambient NO 3− concentration of as low as 0.05 millimolar; however, no NiR induction was found in leaves supplied with NO 2− until the ambient NO 2− concentration was 0.5 millimolar. Nitrate accumulated in NO 2−-fed leaves. The amount of NO 3− accumulating in NO 2−-fed leaves induced similar levels of NiR as did equivalent amounts of NO 3− accumulating in NO 3−-fed leaves. Induction of NiR in NO 2−-fed leaves was not seen until NO 3− was detectable (30 nanomoles/gram fresh weight) in the leaves. The internal concentrations of NO 3−, irrespective of N source, were highly correlated with the levels of NiR induced. When the reduction of NO 3− to NO 2− was inhibited by WO 42−, the induction of NiR was inhibited only partially. The results indicate that in barley leaves NiR is induced by NO 3− directly, i.e. without being reduced to NO 2−, and that absorbed NO 2− induces the enzyme activity indirectly after being oxidized to NO 3− within the leaf. 相似文献
12.
The product of pxcA (formerly known as cotA) is involved in light-induced Na +-dependent proton extrusion. In the presence of 2,5-dimethyl- p-benzoquinone, net proton extrusion by Synechocystis sp. strain PCC6803 ceased after 1 min of illumination and a postillumination influx of protons was observed, suggesting that the PxcA-dependent, light-dependent proton extrusion equilibrates with a light-independent influx of protons. A photosystem I (PS I) deletion mutant extruded a large number of protons in the light. Thus, PS II-dependent electron transfer and proton translocation are major factors in light-driven proton extrusion, presumably mediated by ATP synthesis. Inhibition of CO 2 fixation by glyceraldehyde in a cytochrome c oxidase (COX) deletion mutant strongly inhibited the proton extrusion. Leakage of PS II-generated electrons to oxygen via COX appears to be required for proton extrusion when CO 2 fixation is inhibited. At pH 8.0, NO 3− uptake activity was very low in the pxcA mutant at low [Na +] (~100 μM). At pH 6.5, the pxcA strain did not take up CO 2 or NO 3− at low [Na +] and showed very low CO 2 uptake activity even at 15 mM Na +. A possible role of PxcA-dependent proton exchange in charge and pH homeostasis during uptake of CO 2, HCO 3−, and NO 3− is discussed. 相似文献
13.
An NADPH-dependent NO 2−-reducing system was reconstituted in vitro using ferredoxin (Fd) NADP + oxidoreductase (FNR), Fd, and nitrite reductase (NiR) from the green alga Chlamydomonas reinhardtii. NO 2− reduction was dependent on all protein components and was operated under either aerobic or anaerobic conditions. NO 2− reduction by this in vitro pathway was inhibited up to 63% by 1 mm NADP +. NADP + did not affect either methyl viologen-NiR or Fd-NiR activity, indicating that inhibition was mediated through FNR. When NADPH was replaced with a glucose-6-phosphate dehydrogenase (G6PDH)-dependent NADPH-generating system, rates of NO 2− reduction reached approximately 10 times that of the NADPH-dependent system. G6PDH could be replaced by either 6-phosphogluconate dehydrogenase or isocitrate dehydrogenase, indicating that G6PDH functioned to: (a) regenerate NADPH to support NO 2− reduction and (b) consume NADP +, releasing FNR from NADP + inhibition. These results demonstrate the ability of FNR to facilitate the transfer of reducing power from NADPH to Fd in the direction opposite to that which occurs in photosynthesis. The rate of G6PDH-dependent NO 2− reduction observed in vitro is capable of accounting for the observed rates of dark NO 3− assimilation by C. reinhardtii. 相似文献
14.
Young bean plants ( Phaseolus vulgaris L. var Saxa) were fed with 3.5 or 10 millimolar N in either the form of NO 3− or NH 4+, after being grown on N-free nutrient solution for 8 days. The pH of the nutrient solutions was either 6 or 4. The cell sap pH and the extractable activities of phosphoenolpyruvate carboxylase and of pyruvate kinase from roots and primary leaves were measured over several days. The extractable activity of phosphoenolpyruvate carboxylase (based on soluble protein) from primary leaves increased with NO3− nutrition, whereas with NH4+ nutrition and on N-free nutrient solution the activity remained at a low level. Phosphoenopyruvate carboxylase activity from the roots of NH4+-fed plants at pH 4 was finally somewhat higher than from the roots of plants grown on NO3− at the same pH. There was no difference in activity from the root between the N treatments when pH in the nutrient solutions was 6. The extractable activity of pyruvate kinase from roots and primary leaves seemed not to be influenced by the N nutrition of the plants. The results are discussed in relation to the physiological function of both enzymes with special regard to the postulated functions of phosphoenolpyruvate carboxylase in C3 plants as an anaplerotic enzyme and as part of a cellular pH stat. 相似文献
15.
The effect of water stress on patterns of nitrate reductase activity in the leaves and nodules and on nitrogen fixation were investigated in Medicago sativa L. plants watered 1 week before drought with or without NO 3−. Nitrogen fixation was decreased by water stress and also inhibited strongly by the presence of NO 3−. During drought, leaf nitrate reductase activity (NRA) decreased significantly particularly in plants watered with NO 3−, while with rewatering, leaf NRA recovery was quite important especially in the NO 3−-watered plants. As water stress progressed, the nodular NRA increased both in plants watered with NO 3− and in those without NO 3− contrary to the behavior of the leaves. Beyond −15.10 5 pascal, nodular NRA began to decrease in plants watered with NO 3−. This phenomenon was not observed in nodules of plants given water only. 相似文献
16.
Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco ( Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PK c−). PK c− plants cultivated under a low light intensity (100 μmol m −2 s −1) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PK c (PK c+). PK c− and PK c+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed 14CO 2 during photosynthesis. However, during growth under low light the nighttime, export of previously fixed 14CO 2 by fully expanded PK c− leaves was 40% lower, whereas concurrent respiratory 14CO 2 evolution was 40% higher than that of PK c+ leaves. This provides a rationale for the reduced root growth of the PK c− plants grown at low irradiance. Leaf photosynthetic and export characteristics in PK c− and PK c+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PK c in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low. 相似文献
17.
Salt tolerant spinach ( Spinacia oleracea) and salt sensitive pea ( Pisum sativum) plants were exposed to mild salinity under identical growth conditions. In order to compare the ability of the two species for extra- and intracellular solute compartmentation in leaves, various solutes were determined in intercellular washing fluids and in aqueously isolated intact chloroplasts. In pea plants exposed to 100 millimolar NaCl for 14 days, apoplastic salt concentrations in leaflets increased continuously with time up to 204 (Cl −) and 87 millimolar (Na +), whereas the two ions reached a steady concentration of only 13 and 7 millimolar, respectively, in spinach leaves. In isolated intact chloroplasts from both species, sodium concentrations were not much different, but chloride concentrations were significantly higher in pea than in spinach. Together with data from whole leaf extracts, these measurements permitted an estimation of apoplastic, cytoplasmic, and vacuolar solute concentrations. Sodium and chloride concentration gradients across the tonoplast were rather similar in both species, but spinach was able to maintain much steeper sodium gradients across the plasmamembrane compared with peas. Between day 12 and day 17, concentrations of other inorganic ions in the pea leaf apoplast increased abruptly, indicating the onset of cell disintegration. It is concluded that the differential salt sensitivity of pea and spinach cannot be traced back to a single plant performance. Major differences appear to be the inability of pea to control salt accumulation in the shoot, to maintain steep ion gradients across the leaf cell plasmalemma, and to synthesize compatible solutes. Perhaps less important is a lower selectivity of pea for K +/Na + and NO 3−/Cl − uptake by roots. 相似文献
18.
The growth rate of Chromohalobacter salexigens DSM 3043 can be stimulated in media containing 0.3 M NaCl by a 0.7 M concentration of other salts of Na +, K +, Rb +, or NH 4+, Cl −, Br −, NO 3−, or SO 42− ions. To our knowledge, growth rate stimulation by a general high ion concentration has not been reported for any organism previously. 相似文献
19.
Up to 80% of the total nitrate reductase activity (NRA) determined in vivo in different parts of vegetative tobacco plant ( Nicotiana tabacum) was located in the leaves. The NRA reached a peak when a leaf had expanded to 27% of its final weight and 33% of its final area. Thereafter, with advancing expansion and age of the leaf, the activity declined. This pattern of development of NRA during the ontogenesis of leaves was not influenced by raising the supply of NO 3− from 3 to 6 milliequivalent per cubic decimeter in the substrate solution. The concentration of NO 3− in leaves, stem and root was inversely related to NRA at both NO 3− levels. Raising the supply of K + from 1 to 6 milliequivalent per cubic decimeter at either concentration of NO 3− slowed down the development of NRA in the initial stages of expansion, but promoted it subsequently. The peak of the activity which developed in a leaf of 62% of its final area was higher at the higher supply of K +. The higher activity was maintained thereafter in the expanding and in matured and older leaves. It was concluded that NRA and the pattern of its development in expanding leaves is related to the availability of metabolites and their incorporation into enzyme proteins. Both these processes are influenced by: (a) the vertical profile of concentration of K + in the shoot and (b) the concentration of K + in a leaf, which depend upon its supply. 相似文献
20.
Nitrate (NO 3−) and ammonium (NH 4+) are the main forms of nitrogen available in the soil for plants. Excessive NH 4+ accumulation in tissues is toxic for plants and exclusive NH 4+-based nutrition enhances this effect. Ammonium toxicity syndrome commonly includes growth impairment, ion imbalance and chlorosis among others. In this work, we observed high intraspecific variability in chlorophyll content in 47 Arabidopsis thaliana natural accessions grown under 1 mM NH 4+ or 1 mM NO 3− as N-source. Interestingly, chlorophyll content increased in every accession upon ammonium nutrition. Moreover, this increase was independent of ammonium tolerance capacity. Thus, chlorosis seems to be an exclusive effect of severe ammonium toxicity while mild ammonium stress induces chlorophyll accumulation. 相似文献
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