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2.
Spatial–temporal variation of the regulation and the kinetics of net nitrate (NO 3
−) uptake rate (NNUR) along the tap root of Citrus aurantium L. were analysed. Suberin incrustation in the peripheral cell layers and plasma membrane (PM) H +-ATPase localisation, anatomical and physiological factors involved in NO 3
− uptake were also investigated. The results clearly indicated a spatially uniform distribution of the regulation process,
accompanied by a temporal heterogeneous pattern of the kinetics of NO 3
− uptake along citrus tap root. In particular, kinetic analysis had a biphasic pattern, saturating (high affinity transport
system) and linear (low affinity transport system), in response to increasing external NO 3
− concentrations in each root region, where 200 μM NO 3
− represented the threshold separating these two systems. Kinetic parameters, K
m and V
max, clearly indicated that apical segments reached the maximum value of induction before basal segments. Hence, the apical root
zones, early exhibiting the maximum of potential capacity to absorb the NO 3
−, could be considered more efficient than basal root segments for acquiring NO 3
− from external solution. Suberin incrustations in the hypodermal cell layer, characterised by uniform fluorescence intensity
among the root segments, could be responsible for the unchanged NNUR, while the PM H +-ATPase could explain the temporal pattern of NNUR. 相似文献
3.
Humic acids (HAs) have a major effect on nutrient uptake, metabolism, growth and development in plants. Here, we evaluated the effect of HA pretreatment applied with a nutrient solution on the uptake kinetics of nitrate nitrogen (N‐NO 3?) and the metabolism of nitrogen (N) in rice under conditions of high and low NO 3? supply. In addition, the kinetic parameters of NO 3? uptake, N metabolites, and nitrate transporters (NRTs) and the plasma membrane (PM) H +‐ATPase gene expression were examined. The plants were grown in a growth chamber with modified Hoagland and Arnon solution until 21 days after germination (DAG), and they were then transferred to a solution without N for 48 h and then to another solution without N and with and without the addition of HAs for another 48 h. After this period of N deprivation, the plants received new nutrient solutions containing 0.2 and 2.0 mM N‐NO 3?. Treatment of rice plants with HA promoted the induction of the genes OsNRT2.1‐2.2/ OsNAR2.1 and some isoforms PM H +‐ATPase in roots. The application of HAs differentially modified the parameters of the uptake kinetics of NO 3? under both concentrations. When grown with 0.2 mM NO 3?, the plants pretreated with HA had lower Km and Cmin values as well as a higher Vmax/ Km ratio. When grown with 2 mM NO 3?, the plants pretreated with HA had a higher Vmax value, a greater root and shoot mass, and a lower root/shoot ratio. The N fractions were also altered by pretreatment with HA, and a greater accumulation of NO 3? and N‐amino was observed in the roots and shoots, respectively, of plants pretreated with HA. The results suggest that pretreatment with HA modifies root morphology and gene expression of PM H +‐ATPases and NO 3? transporters, resulting in a greater efficiency of NO 3? acquisition by high‐ and low‐affinity systems. 相似文献
4.
High salinity and nitrogen (N) deficiency in soil are two key factors limiting crop productivity, and they usually occur simultaneously. Here we firstly found that H +‐PPase is involved in salt‐stimulated NO 3? uptake in the euhalophyte Salicornia europaea. Then, two genes (named SeVP1 and SeVP2) encoding H +‐PPase from S. europaea were characterized. The expression of SeVP1 and SeVP2 was induced by salt stress and N starvation. Both SeVP1 or SeVP2 transgenic Arabidopsis and wheat plants outperformed the wild types (WTs) when high salt and low N occur simultaneously. The transgenic Arabidopsis plants maintained higher K +/Na + ratio in leaves and exhibited increased NO 3? uptake, inorganic pyrophosphate‐dependent vacuolar nitrate efflux and assimilation capacity under this double stresses. Furthermore, they had more soluble sugars in shoots and roots and less starch accumulation in shoots than WT. These performances can be explained by the up‐regulated expression of ion, nitrate and sugar transporter genes in transgenic plants. Taken together, our results suggest that up‐regulation of H +‐PPase favours the transport of photosynthates to root, which could promote root growth and integrate N and carbon metabolism in plant. This work provides potential strategies for improving crop yields challenged by increasing soil salinization and shrinking farmland. 相似文献
5.
Plasma membrane H+-ATPase (PM H+-ATPase, EC 3.6.1.3.) is a proton pump that is necessary to promote cell growth and ion fluxes across the plasma membrane. The main goal of this study was to evaluate the role of PM H+-ATPase isoform OsA7 expression in rice growth and nitrogen (N) accumulation using three genetically engineered lineages with artificial micro RNA (amiRNA) targeting OsA7 (osa7.1, osa7.2, and osa7.3). PM H+-ATPase isoform expression in rice shoots and roots (wild-type) revealed that OsA7 is highly expressed in roots and is the most highly expressed PM H+-ATPase isoform. The three osa7 lineages had lower fresh weight, grain yield, height, and 1000-grain weight compared to control IRS plants. The hydroponic experiment comprised three NO3− levels over 30 days: 0.2 mM NO3−–N, 2.0 mM NO3−–N, and NO3− starvation for 3 days. The three osa7 lineages had lower PM H+-ATPase and V-H+-PPase activity as compared to the IRS plants. The root and shoot fresh weights were lower in osa7 lineages. The root/shoot ratio was lower in the osa7 lineages cultivated without nitrogen for 3 days and with 0.2 mM of NO3−–N as compared to IRS, and did not change in plants cultivated with 2.0 mM NO3−–N. The total N concentration did not change in the three osa7 lineages as compared to IRS. Overall, the results indicate that OsA7 is important for rice growth, grain production, and root growth, but does not affect N accumulation, highlighting the importance of other PM H+-ATPase isoforms in N uptake. 相似文献
6.
Glucose‐6‐phosphate dehydrogenase (G6PDH) is important for the activation of plant resistance to environmental stresses, and ion homeostasis is the physiological foundation for living cells. In this study, we investigated G6PDH roles in modulating ion homeostasis under salt stress in Carex moorcroftii callus. G6PDH activity increased to its maximum in 100 m M NaCl treatment and decreased with further increased NaCl concentrations. K +/Na + ratio in 100 m M NaCl treatment did not exhibit significant difference compared with the control; however, in 300 m M NaCl treatment, it decreased. Low‐concentration NaCl (100 m M) stimulated plasma membrane (PM) H +‐ATPase and NADPH oxidase activities as well as Na +/H + antiporter protein expression, whereas high‐concentration NaCl (300 mM) decreased their activity and expression. When G6PDH activity and expression were reduced by glycerol treatments, PM H +‐ATPase and NADPH oxidase activities, Na +/H + antiporter protein level and K +/Na + ratio dramatically decreased. Simultaneously, NaCl‐induced hydrogen peroxide (H 2O 2) accumulation was abolished. Exogenous application of H 2O 2 increased G6PDH, PM H +‐ATPase and NADPH oxidase activities, Na +/H + antiporter protein expression and K +/Na + ratio in the control and glycerol treatments. Diphenylene iodonium (DPI), the NADPH oxidase inhibitor, which counteracted NaCl‐induced H 2O 2 accumulation, decreased G6PDH, PM H +‐ATPase and NADPH oxidase activities, Na +/H + antiporter protein level and K +/Na + ratio. Western blot result showed that G6PDH expression was stimulated by NaCl and H 2O 2, and blocked by DPI. Taken together, G6PDH is involved in H 2O 2 accumulation under salt stress. H 2O 2, as a signal, upregulated PM H +‐ATPase activity and Na +/H + antiporter protein level, which subsequently resulted in the enhanced K +/Na + ratio. G6PDH played a central role in the process. 相似文献
8.
Ion-selective microelectrodes were used to measure NH 4+, NO 3– and H + fluxes along the primary root of maize seedlings. Plants were exposed to nutrient solutions containing NH 4+, NO 3– or both ions. Nitrogen fluxes along the root varied substantially among the different treatments. Net NH 4+ and NO 3– uptake and H + extrusion were low at the very apex of the root and generally increased in the more basal regions. In the absence of nitrogen or in the presence of NO 3– alone, net H + uptake (and root surface alkalinization) occurred at the root tip (0–1 mm), whereas net H + extrusion occurred in all other regions. In the presence of NH 4+ alone, a dramatic increase in net H + extrusion was detected in all regions except for the region 6–11 mm from the apex. In contrast, when NO 3– alone was supplied, net H + extrusion was depressed at all locations except for the tip (0–1 mm). When both NH 4+ and NO 3– were supplied, NO 3– uptake was suppressed at all locations while net H + extrusion was increased relative to NO 3– alone. The capacities to absorb NH 4+ and NO 3– at the tip were similar, as indicated by flux rates when NH 4+ or NO 3– were supplied as sole sources, but when supplied together, net NO 3– uptake was half that of net NH 4+ uptake, indicating that NH 4+ may satisfy the nitrogen requirements of the poorly vascularized apical tissue in the most energy-efficient way. The high spatial resolution of the measurements enabled us to establish that acidification in the root expansion zone is maintained regardless of nitrogen source. 相似文献
9.
The effect of pH on nitrate and ammonium uptake in the high‐affinity transport system and low‐affinity transport system ranges was compared in two conifers and one crop species. Many conifers grow on acidic soils, thus their preference for ammonium vs nitrate uptake can differ from that of crop plants, and the effect of pH on nitrogen (N) uptake may differ. Proton, ammonium and nitrate net fluxes were measured at seedling root tips and 5, 10, 20 and 30 mm from the tips using a non‐invasive microelectrode ion flux measurement system in solutions of 50 or 1500 µ M NH 4NO 3 at pH 4 and 7. In Glycine max and Pinus contorta, efflux of protons was observed at pH 7 while pH 4 resulted in net proton uptake in some root regions. Pseudotsuga menziesii roots consistently showed proton efflux behind the root tip, and thus appear better adapted to maintain proton efflux in acid soils. P. menziesii's ability to maintain ammonium uptake at low pH may relate to its ability to maintain proton efflux. In all three species, net nitrate uptake was greatest at neutral pH. Net ammonium uptake in G. max and net nitrate uptake in P. menziesii were greatly reduced at pH 4, particularly at high N concentration, thus N concentration should be considered when determining optimum pH for N uptake. In P. menziesii and G. max, net N uptake was greater in 1500 than 50 µ M NH 4NO 3 solution, but flux profiles of all ions varied among species. 相似文献
10.
We report here on an investigation of net nitrate and proton fluxes in root cells of maize ( Zea mays L.) seedlings grown without (noninduced) and with (induced) 0.1 millimolar nitrate. A microelectrode system described previously (IA Newman, LV Kochian, MA Grusak, WJ Lucas [1987] Plant Physiol 84: 1177-1184) was utilized to quantify net ionic fluxes from the measurement of electrochemical potential gradients for NO 3− and H + within the unstirred layer at the root surface. The nitrate-inducibility, pH dependence, and concentration dependence of net NO 3− uptake correlated quite closely with the electrical response of maize roots to nitrate under the same experimental conditions (as described in PR McClure, LV Kochian, RM Spanswick, JE Shaff [1990] Plant Physiol 93: 281-289). Additionally, it was found that potential inhibitors of the plasmalemma H +-ATPase (vandate, diethylstilbestrol), which were shown to abolish the electrical response to NO 3− (in PR McClure, LV Kochian, RM Spanswick, JE Shaff [1990] Plant Physiol 93: 281-289), dramatically inhibited NO 3− absorption. These results strongly indicate that the NO 3− electrical response is due to the operation of a NO 3− transport system in the plasmalemma of maize root cells. Furthermore, the results from the H +-ATPase inhibitor studies indicate that the NO 3− transport system is linked to the H +-ATPase, presumably as a NO 3−/H + symport. This is further supported by the pH response of the NO 3− transport system (inhibition at alkaline pH values) and the change in net H + flux from a moderate efflux in the absence of NO 3−, to zero net H + flux after exposing the maize root to exogenous nitrate. Although these results can be explained by other interpretations, the simplest model that fits both the electrical responses and the NO 3−/H + flux data is a NO 3−/H + symport with a NO 3−:H + flux stoichiometry >1, whose operation results in the stimulation of the H +-ATPase due to the influx of protons through the cotransport system. 相似文献
13.
Previously, we reported that in Citrus plants, nitrate influx through the plasmalemma of roots cells follows a biphasic pattern, suggesting the existence of at least two different uptake systems, a high and low affinity transport system (HATS and LATS, respectively). Here, we describe a novel inducible high affinity transport system (iHATS). This new nitrate transport system has a high capacity to uptake nitrate in two different Citrus rootstocks (Cleopatra mandarin and Troyer citrange). The iHATS was saturable, showing higher affinity than constitutive high affinity transport system (cHATS) to the substrate NO 3−. The V max for this saturable component iHATS was higher than cHATS, reaching similar values in both rootstocks.Additionally, we studied the regulation of root NO 3− uptake mediated by both HATS (iHATS and cHATS) and LATS. In both rootstocks, cHATS is constitutive and independent of N-status. Concerning the regulation of iHATS, this system is upregulated by NO 3− and down-regulated by the N status and by NO 3− itself when plants are exposed to it for a longer period of time. LATS in Cleopatra mandarin and Troyer citrange rootstocks is repressed by the N-status.The use of various metabolic uncouplers or inhibitors indicated that NO 3− net uptake mediated by iHATS and LATS was an active transport system in both rootstocks.Key Words: Citrus, inducible high affinity transport system (iHATS), constitutive high affinity transport system (cHATS), nitrate uptake, regulation 相似文献
15.
Hydrogen sulphide (H 2S) is emerging as an important signalling molecule involved in plant resistance to various stresses. However, the underlying mechanism of H 2S in aluminium (Al) resistance and the crosstalk between H 2S and nitric oxide (NO) in Al stress signalling remain elusive. Citrate secretion is a wide‐spread strategy for plants against Al toxicity. Here, two citrate transporter genes, GmMATE13 and GmMATE47, were identified and characterized in soybean. Functional analysis in Xenopus oocytes and transgenic Arabidopsis showed that GmMATE13 and GmMATE47 mediated citrate exudation and enhanced Al resistance. Al treatment triggered H 2S generation and citrate exudation in soybean roots. Pretreatment with an H 2S donor significantly elevated Al‐induced citrate exudation, reduced Al accumulation in root tips, and alleviated Al‐induced inhibition of root elongation, whereas application of an H 2S scavenger elicited the opposite effect. Furthermore, H 2S and NO mediated Al‐induced GmMATE expression and plasma membrane (PM) H +‐ATPase activity and expression. Further investigation showed that NO induced H 2S production by regulating the key enzymes involved in biosynthesis and degradation of H 2S. These findings indicate that H 2S acts downstream of NO in mediating Al‐induced citrate secretion through the upregulation of PM H +‐ATPase‐coupled citrate transporter cotransport systems, thereby conferring plant resistance to Al toxicity. 相似文献
17.
Methyl jasmonate (MeJA) elicits stomatal closure in many plant species. Stomatal closure is accompanied by large ion fluxes across the plasma membrane (PM). Here, we recorded the transmembrane ion fluxes of H +, Ca 2+ and K + in guard cells of wild‐type (Col‐0) Arabidopsis, the CORONATINE INSENSITIVE1 ( COI1) mutant coi1‐1 and the PM H +‐ATPase mutants aha1‐6 and aha1‐7, using a non‐invasive micro‐test technique. We showed that MeJA induced transmembrane H + efflux, Ca 2+ influx and K + efflux across the PM of Col‐0 guard cells. However, this ion transport was abolished in coi1‐1 guard cells, suggesting that MeJA‐induced transmembrane ion flux requires COI1. Furthermore, the H + efflux and Ca 2+ influx in Col‐0 guard cells was impaired by vanadate pre‐treatment or PM H +‐ATPase mutation, suggesting that the rapid H + efflux mediated by PM H +‐ATPases could function upstream of the Ca 2+ flux. After the rapid H + efflux, the Col‐0 guard cells had a longer oscillation period than before MeJA treatment, indicating that the activity of the PM H +‐ATPase was reduced. Finally, the elevation of cytosolic Ca 2+ concentration and the depolarized PM drive the efflux of K + from the cell, resulting in loss of turgor and closure of the stomata. 相似文献
18.
Poplar plants are cultivated as woody crops, which are often fertilized by addition of ammonium (NH 4 +) and/or nitrate (NO 3 ?) to improve yields. However, little is known about net NH 4 +/NO 3 ? fluxes and their relation with H + fluxes in poplar roots. In this study, net NH 4 +/NO 3 ? fluxes in association with H + fluxes were measured non-invasively using scanning ion-selective electrode technique in fine roots of Populus popularis. Spatial variability of NH 4 + and NO 3 ? fluxes was found along root tips of P. popularis. The maximal net uptake of NH 4 + and NO 3 ? occurred, respectively, at 10 and 15 mm from poplar root tips. Net NH 4 + uptake was induced by ca. 48 % with provision of NO 3 ? together, but net NO 3 ? uptake was inhibited by ca. 39 % with the presence of NH 4 + in poplar roots. Furthermore, inactivation of plasma membrane (PM) H +-ATPases by orthovanadate markedly inhibited net NH 4 +/NO 3 ? uptake and even led to net NH 4 + release with NO 3 ? co-provision. Linear correlations were observed between net NH 4 +/NO 3 ? and H + fluxes in poplar roots except that no correlation was found between net NH 4 + and H + fluxes in roots exposed to NH 4Cl and 0 mM vanadate. These results indicate that root tips play a key role in NH 4 +/NO 3 ? uptake and that net NH 4 +/NO 3 ? fluxes and the interaction of net fluxes of both ions are tightly associated with H + fluxes in poplar roots. 相似文献
19.
This study concerns the inhibitory effects of acid pH and nickel on growth, nutrient (NO 3
- and NH 4
+) uptake, carbon fixation, O 2 evolution, electron transport chain and enzyme (nitrate reductase and ATPase) activities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with decreasing pH, the tolerant strain was found to be metabolically more active than the wild-type. A reduced cation (NH 4
+, Na +, K + and Ca 2+) uptake, coupled with a facilitated influx of anions (NH 4
+, PO 4
3- and HCO 3
-), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase activity at decreasing pH revealed the involvement of superactive ATPase in exporting H + ions and keeping the internal pH neutral. A difference in Na + and K + efflux of the two strains at decreasing pH suggests there is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought about by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane potential and permeability not only offers protection against acidity, but also co-tolerance to metals. 相似文献
20.
As a major antioxidant in plants, ascorbic acid (AsA) plays a very important role in the response to aluminum (Al) stress. However, the effect of AsA on the mitigation of Al toxicity and the mechanism of nitrate nitrogen (NO 3 ?–N) uptake by plants under Al stress are unclear. In this study, a hydroponic experiment was conducted using peak 1 A rice (sterile line, Indica) with weaker resistance to Al and peak 1 superior 5 rice (F1 hybrid, Indica) with stronger resistance to Al to study the effects of exogenous AsA on the physiological and biochemical responses to NO 3 ?–N uptake by rice roots exposed to 50 μmol L ?1 Al. Al stress induced increases in the concentrations of H 2O 2 and malondialdehyde (MDA) and in the activities of antioxidant enzymes [such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)]. Plasma membrane (PM) H +-ATPase and H +-pump activities, endogenous AsA content and NO 3 ?–N uptake in rice roots decreased under Al stress. After treatment with 2 mmol L ?1 exogenous AsA combined with Al, concentrations of H 2O 2 and MDA in roots notably decreased, and endogenous AsA content and activities of SOD, POD, CAT, and APX in rice roots increased significantly; furthermore, the interaction of PM H +-ATPase and the 14-3-3 protein was also enhanced significantly compared with that in control plants without AsA treatment, which clearly increased NO 3 ?–N uptake. Based on all of these data, the application of AsA significantly reduced the accumulation of H 2O 2 and MDA and increased the activities of PM H +-ATPase and the H +-pump by increasing the endogenous AsA content, the antioxidant enzyme activities, and the interaction of PM H +-ATPase and the 14-3-3 protein in the roots of the two rice cultivars under Al stress, thereby improving the uptake of NO 3 ?–N in rice. 相似文献
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