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1.
The substrate and ionic requirements of ATP and inorganic pyrophosphate (PPi) hydrolysis by tonoplast vesicles isolated from storage tissue of red beet (Beta vulgaris L.) were compared with the requirements of ATP-and PPi-dependent proton translocation by the same material. Both ATP hydrolysis and ATP-dependent proton translocation are most stimulated by Cl and inhibited by NO3. NaCl and KCl support similar rates of ATP hydrolysis and ATP-dependent proton translocation while K2SO4 supports lesser rates for both. PPi hydrolysis and PPi-dependent proton translocation are most stimulated by K+. KCl and K2SO4 support similar rates of PPi hydrolysis and PPi-dependent proton translocation but NaCl has only a small stimulatory effect on both. Since PPi does not inhibit ATP hydrolysis and ATP does not interfere with PPi hydrolysis, it is inferred that the two phosphohydrolase and proton translocation activities are mediated by different tonoplast-associated enzymes. The results indicate the presence of an energy-conserving proton-translocating pyrophosphatase in the tonoplast of red beet.  相似文献   

2.
Sealed microsomal vesicles were prepared from corn (Zea mays, Crow Single Cross Hybrid WF9-Mo17) roots by centrifugation of a 10,000 to 80,000g microsomal fraction onto a 10% dextran T-70 cushion. The Mg2+-ATPase activity of the sealed vesicles was stimulated by Cl and NH4+ and by ionophores and protonophores such as 2 micromolar gramicidin or 10 micromolar carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP). The ionophore-stimulated ATPase activity had a broad pH optimum with a maximum at pH 6.5. The ATPase was inhibited by NO3, was insensitive to K+, and was not inhibited by 100 micromolar vanadate or by 1 millimolar azide.

Quenching of quinacrine fluorescence was used to measure ATP-dependent acidification of the intravesicular volume. Quenching required Mg2+, was stimulated by Cl, inhibited by NO3, was insensitive to monovalent cations, was unaffected by 200 micromolar vanadate, and was abolished by 2 micromolar gramicidin or 10 micromolar FCCP. Activity was highly specific for ATP. The ionophore-stimulated ATPase and ATP-dependent fluorescence quench both required a divalent cation (Mg2+ ≥ Mn2+ > Co2+) and were inhibited by high concentrations of Ca2+. The similarity of the ionophore-stimulated ATPase and quinacrine quench and the responses of the two to ions suggest that both represent the activity of the same ATP-dependent proton pump. The characteristics of the proton-translocating ATPase differed from those of the mitochondrial F1F0-ATPase and from those of the K+-stimulated ATPase of corn root plasma membranes, and resembled those of the tonoplast ATPase.

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3.
Abstract. Nitrate uptake into Chara corallina cells at different external pH (pHo) after different NO3 pretreatment conditions has been investigated. Following NO3 pretreatment (0.2 mol m−3 NO3) there was little effect of pHo on subsequent net NO3 uptake into Chara cells. After N deprivation (2 mmol m−3 NO3) there was a pronounced effect of pHo on nitrate uptake, the maximum rate occurring at pHo 4.7. There was no consistent relationship between OH efflux and NO3 uptake in short term experiments (< 1 h). NO3 efflux was also sensitive to pHo, the maximum rate occurring at ∼ pHo 5.0. An inhibitor of the proton pump, DES, immediately stimulated NO3 uptake into cells pretreated with NO3 and prevented the time-dependent decrease in NO3, uptake into Chara cells that had been previously treated with low N (2 mmol m−3 NO3). NO3 efflux was found to be very sensitive to DES with Ki= 0.7 mmol m−3. At the optimum pHo for NO3 uptake the effect of DES on membrane potential (ψm) were slight, and only apparent after 30 min. The results are interpreted in context of current models relating NO3 uptake and H+ pump activity. A new model for NO3 uptake is proposed which involves NO3/NO3 exchange at steady state.  相似文献   

4.
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   

5.
Isolated frog gastric mucosa was used to study the separation of formation of protons (or their precursors) from proton translocation by using various inhibitors. Both thiocyanate (SCN) and nitrite (NO2) inhibit the acid secretion in spontanously secreting mucosa. The inhibition is reversed when the inhibitor is removed such that the excess acid secreted above baseline in the ‘off’-period compensates for the amount inhibited in the ‘on’-period. Both agents also inhibit the effect on acid secretion of pulse stimulation with histamine though to a lesser extent. Upon removal of the inhibitor, the total amount of acid secreted in excess of basal is equal to that observed with histamine alone. Likewise, metiamide, an H2-antagonist, also inhibits acid secretion with or without histamine. However, in contrast to SCN and NO2, removal of this inhibitor is without effect on the acid-secretion rate. These results indicate that both SCN and NO2 inhibit the proton translocation rather than the formation of protons or their precursors as is the case with metiamide.  相似文献   

6.
Mg:ATP-dependent H+ pumping has been studied in microsomal vesicles from 24-hour-old radish (Raphanus sativus L.) seedlings by monitoring both intravesicular acidification and the building up of an inside positive membrane potential difference (Δ ψ). ΔpH was measured as the decrease of absorbance of Acridine orange and Δ ψ as the shift of absorbance of bis(3-propyl-5-oxoisoxazol-4-yl)pentamethine oxonol. Both Mg:ATP-dependent Δ pH and Δ ψ generation are completely inhibited by vanadate and insensitive to oligomycin; moreover, Δ pH generation is not inhibited by NO3. These findings indicate that this membrane preparation is virtually devoid of mitochondrial and tonoplast H+-ATPases. Both intravesicular acidification and Δ ψ generation are influenced by anions: Δ pH increases and Δ ψ decreases following the sequence SO42−, Cl, Br, NO3. ATP-dependent H+ pumping strictly requires Mg2+. It is very specific for ATP (apparent Km 0.76 millimolar) compared to GTP, UTP, CTP, ITP. Δ pH generation is inhibited by CuSO4 and diethylstilbestrol as well as vanadate. Δ pH generation is specificially stimulated by K+ (+ 80%) and to a lesser extent by Na+ and choline (+28% and +14%, respectively). The characteristics of H+ pumping in these microsomal vesicles closely resemble those described for the plasma membrane ATPase partially purified from several plant materials.  相似文献   

7.
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 CO2 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 CO2 fixation is inhibited. At pH 8.0, NO3 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 CO2 or NO3 at low [Na+] and showed very low CO2 uptake activity even at 15 mM Na+. A possible role of PxcA-dependent proton exchange in charge and pH homeostasis during uptake of CO2, HCO3, and NO3 is discussed.  相似文献   

8.
The presence of an electrogenic pump in pea stem microsomal vesicles has already been demonstrated, but no evidence on the nature of the electrogenic ion has been presented (Rasi-Caldogno, F., De Michelis, M.I. and Pugliarello, M.C. (1981) Biochim. Biophys. Acta 642, 37–45). In this work we tested the usefulness of the ΔpH probe Acridine orange to monitor both ATP-dependent and ionophore-induced H+ fluxes in pea stem microsomal vesicles. The H+/K+ exchanger nigericin causes a marked uptake of protons into the vesicles that can be followed, with similar results, both as Acridine orange absorbance changes and pH changes of the external medium. ATP induces an uptake of Acridine orange into the vesicles which is reversed by FCCP and abolished by the presence of Triton X-100 in the incubation medium, thus indicating an inward, ATP-driven, H+ translocation. The ATP-dependent acridine orange uptake is Mg2+-requiring and KCl-stimulated. Such activity is inhibited by two specific ATPase inhibitors, dicyclohexylcarbodiimide and diethylstilbestrol, while it is unaffected by oligomycin and Na3VO4. These results show that Acridine orange is a useful probe to measure pH gradients in our membrane system and are consistent with the hypothesis that an ATPase of plasmalemma may act as a proton pump.  相似文献   

9.
Nitrogen form has been shown to affect Zn uptake, translocation and storage in the Zn-hyperaccumulating plant Noccaea caerulescens but the biochemical processes are not fully understood. Organic acids and amino acids have been implicated in Zn transport and storage. This study aimed to examine the effect of N form on concentrations of organic acids and amino acids and how these metabolites correlated with Zn hyperaccumulation. Plants were grown in nutrient solution with NO3, NH4NO3 or NH4+, supplied with 50 or 300 μM Zn, and buffered at either pH 4.5 or 6.5. The metabolomic profile was determined by gas chromatography mass spectroscopy. The concentration of Zn in shoots, xylem and roots was greatest for the NO3, pH 6.5 and 300 μM Zn treatments. For all N forms, the lower growth-medium pH raised xylem sap pH but had no influence on Zn concentration or exudation rate of the xylem sap. Nitrate enhanced organic acid production while NH4+ increased amino acid production. Organic acids in the xylem were more responsive to changes in growth-medium pH than N form, and did not correlate with Zn concentration in shoots, roots or xylem. Serine might be directly involved in Zn hyperaccumulation. Phosphoric acid was associated with reduced Zn accumulation in the shoots. Malic acid was not detected in the shoots but responded to cation uptake more than to Zn specifically in the roots. Citric acid responded to cation uptake more than to Zn specifically in the shoots but did not correlate with Zn concentration in the roots or the xylem sap, or any other cations in the roots. In conclusion, organic acids in N. caerulescens are not specifically involved in Zn hyperaccumulation but are involved in regulating pH in the xylem and cation–anion balance in plants.  相似文献   

10.
In soybean (Glycine max L. Merr. cv Kingsoy), NO3 assimilation in leaves resulted in production and transport of malate to roots (B Touraine, N Grignon, C Grignon [1988] Plant Physiol 88: 605-612). This paper examines the significance of this phenomenon for the control of NO3 uptake by roots. The net NO3 uptake rate by roots of soybean plants was stimulated by the addition of K-malate to the external solution. It was decreased when phloem translocation was interrupted by hypocotyl girdling, and partially restored by malate addition to the medium, whereas glucose was ineffective. Introduction of K-malate into the transpiration stream using a split root system resulted in an enrichment of the phloem sap translocated back to the roots. This treatment resulted in an increase in both NO3 uptake and C excretion rates by roots. These results suggest that NO3 uptake by roots is dependent on the availability of shoot-borne, phloem-translocated malate. Shoot-to-root transport of malate stimulated NO3 uptake, and excretion of HCO3 ions was probably released by malate decarboxylation. NO3 uptake rate increased when the supply of NO3 to the shoot was increased, and decreased when the activity of nitrate reductase in the shoot was inhibited by WO42−. We conclude that in situ, NO3 reduction rate in the shoot may control NO3 uptake rate in the roots via the translocation rate of malate in the phloem.  相似文献   

11.
Maas EV 《Plant physiology》1969,44(7):985-989
Ca2+ uptake was studied in short-term experiments using 5-day-old excised maize roots. This tissue readily absorbs Ca2+, and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated. The uptake of Ca2+, like that of other cations, is influenced by the counter ion, the pH and concentration of the ambient solution, and the presence of other cations. The rate of uptake from various salts decreases in the following order: NO3 > Cl = Br > SO42−. K+ and H+ greatly interfere with Ca2+ absorption, while Li+ and Na+ have only slight effects.  相似文献   

12.
Proton transport in isolated vacuoles from corn coleoptiles   总被引:7,自引:4,他引:3       下载免费PDF全文
Mandala S  Taiz L 《Plant physiology》1985,78(1):104-109
Vacuoles were isolated from corn coleoptile protoplasts and ATP-dependent proton transport was measured by quinacrine fluorescence quenching or by the uptake of [14C]methylamine. Intact vacuoles were judged to be free of a surrounding plasma membrane based on fluorescent staining with fluoroscein-diacetate. Essentially all of the detectable ATP-stimulated methylamine uptake and α-mannosidase activities present in intact protoplasts were recovered in isolated vacuoles. In contrast, the activities of marker enzymes for plasma membranes, Golgi, endoplasmic reticulum, and mitochondria were reduced to 5 to 17% in vacuolar preparations. The characteristics of proton pumping by isolated vacuoles were compared to those of light microsomal membranes possibly derived from the tonoplast. ATP-dependent proton pumping by both isolated vacuoles and light microsomal vesicles was stimulated by Cl, and inhibited by NO3, carbonyl cyanide-m-chlorophenylhydrazone, N,N′-dicyclohexylcarbodiimide, N-ethylmaleimide, 4,4′-diisothiocyano-2,2′-stilbene disulfonic acid, diethylstilbestrol, and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, but not by vanadate. Both activities also showed substrate specificity for Mg-ATP. Finally, proton transport activities of vacuolar and microsomal fractions exhibited similar profiles after flotation in linear dextran gradients. We conclude that the microsomal proton pump previously characterized in corn coleoptiles (Mettler et al. 1982 Plant Physiol 70: 1738-1742) is derived from the tonoplast.  相似文献   

13.
Uptake of Metal Ions by Rhizopus arrhizus Biomass   总被引:10,自引:1,他引:9       下载免费PDF全文
Rhizopus arrhizus biomass was found to absorb a variety of different metal cations and anions but did not absorb alkali metal ions. The amount of uptake of the cations was directly related to ionic radii of La3+, Mn2+, Cu2+, Zn2+, Cd2+, Ba2+, Hg2+, Pb2+, UO22+, and Ag+. The uptake of all the cations is consistent with absorption of the metals by sites in the biomass containing phosphate, carboxylate, and other functional groups. The uptake of the molybdate and vanadate anions was strongly pH dependent, and it is proposed that the uptake mechanism involves electrostatic attraction to positively charged functional groups.  相似文献   

14.
Effects of endotoxin administration on the ATP-dependent Ca2+ uptake by canine cardiac sarcoplasmic reticulum (SR) were investigated. Results obtained 4 h after endotoxin administration show that ATP-dependent Ca2+ uptake by cardiac SR was decreased by 27–43% (p < 0.05). Kinetic analysis indicates that the Vmax values for Ca2+ and for ATP were significantly decreased while the S0.5 and the Hill coefficient values were not affected during endotoxin shock. Magnesium (1–5 mM) stimulated while vanadate (25–50 M) inhibited the ATP-dependent Ca2+ uptake, but the Mg2+-stimulated and the vanadate-inhibited activities remained significantly lower in the endotoxin-treated animals. Phosphorylation of SR by the exogenously added catalytic subunit of the cAMP-dependent protein kinase or by the addition of calmodulin stimulated the ATP-dependent Ca2+ uptake activities both in the control and endotoxin-injected dogs. However, the phosphorylation-stimulated activities remained significantly lower in the endotoxin-injected dogs. Dephosphorylation of SR decreased the ATP-dependent Ca2+ uptake, but the half-time required for the maximal dephosphorylation was reduced by 31% (p < 0.05) 4 h post-endotoxin. These data indicate that endotoxin administration impairs the ATP-dependent Ca2+ uptake in canine cardiac SR and the endotoxininduced impairment in the SR calcium transport is associated with a mechanism involving a defective phosphorylation and an accelerated dephosphorylation of SR membrane protein. Since ATP-dependent Ca2+ uptake by cardiac SR plays an important role in the regulation of the homeostatic levels of the contractile calcium, our findings may provide a biochemical explanation for myocardial dysfunction that occurs during endotoxin shock.  相似文献   

15.
Respiration-driven proton translocation has been studied with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing H2 during reduction of O2, NO?3, NO?2 or N2O. A simplified scheme of anaerobic electron transport and associated proton translocation is shown that is consistent with the measured H+oxidant ratios. Furthermore, the kinetics and energetics of NO?3 uptake in whole cells of P. denitrificans were studied. For this purpose, we measured H2 consumption or N2O production after addition of NO?3 to a cell suspension, which indirectly gave information about uptake (and reduction) of NO?3. It was found that a lag phase in H2 consumption or N2O production appeared whenever the membrane potential was dissipated by addition of thiocyanate, carbonyl cyanide m-chlorophenylhydrazone or triphenyl-methylphosphonium bromide. However, these lag phases were not observed when NO?2 was present at the moment of introduction of NO?3. On the basis of these findings we conclude that there are two uptake systems for NO?3. One system is dependent on the proton-motive force and is probably used for initiation of NO?3 uptake. The other is an NO?3NO?2 antiport and its function is to take over NO?3 uptake from the first system.  相似文献   

16.
Sealed plasma membrane vesicles were obtained in high purity from leaves of Commelina communis L. by aqueous two-phase partitioning. Based on the analysis of a range of markers, the preparations (U3+U3′ phases) were shown to be devoid of tonoplast, Golgi and thylakoid membranes, and showed only trace mitochondrial contamination. One-third of the vesicles were oriented inside out and exhibited ATP-driven 45Ca2+ transport [? 15 pkat (mg protein)−1]. Ca2+ uptake into the vesicles had a pH optimum of 7.2 and apparent Km values for Ca2+ of 4.4 μM and for Mg-ATP of 300 μM. Ca2+ uptake, K+, Mg2+-ATPase (EC 3.6.1.3) activity as well as glucan synthase II (EC 2.4.1.34) activity were all maximal at the same equilibrium density (1.17 g cm−3) on continuous sucrose density gradients. The protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP) did not inhibit the ATP-dependent Ca2+ transport into the vesicles, excluding a Ca2+/H+ exchange driven by a proton gradient. ATP-dependent Ca2+ uptake was inhibited by erythrosin B (I50= 0.1 μM), ruthenium red (I50= 30 μM), La3+ (I50= 10 μM) and vanadate (I50= 500 μM), but not by azide, cyanide and oligomycin. The calmodulin antagonists, trifluoperazine (I50= 70 μM) and W-7 (I50= 100 μM) were also inhibitory, However, this inhibition was not overcome by calmodulin. Trifluoperazine and W-7, on the other hand, stimulated Ca2+ efflux from the vesicles rather than inhibit Ca2+ uptake. Our results demonstrate the presence of a Ca2+-ATPase in the plasma membrane of C. communis. In the intact cell, the enzyme would pump Ca2+ out of the cell. Its high affinity for Ca2+ makes it a likely component involved in adjusting low cytoplasmic Ca2+ levels. No indications for a secondary active Ca2+/H+ transport mechanism in the plasma membrane of C. communis were obtained. Both, the nucleotide specificity and the sensitivity towards vanadate. distinguish the Ca2+-ATPase from the H+-translocating K+. Mg2+-ATPase in C. communis plasma membranes.  相似文献   

17.
The effects of spegazzinine, a dihydroindole alkaloid, on mitochondrial oxidative phosphorylation were studied.Spegazzinine inhibited coupled respiration and phosphorylation in rat liver mitochondria. The I50 was 120 μM. Uncouplers released the inhibition of coupled respiration. Arsenate-stimulated mitochondrial respiration was partially inhibited by spegazzinine. The stimulation of mitochondrial respiration by Ca2+ and the proton ejection associated with the ATP-dependent Ca2+ uptake were not affected by the alkaloid.Oxidative phosphorylation and the Pi-ATP exchange reaction of phosphorylating beef heart submitochondrial particles were strongly inhibited by spegazzinine (I50, 50 μM) while the ATP-dependent reactions, reduction of NAD+ by succinate and the pyridine nucleotides transhydrogenase were less sensitive (I50, 125 μM). Oxygen uptake by submitochondrial particles was not affected.The 2,4-dinitrophenol-stimulated ATPase activity of rat liver mitochondria was not affected by 300 μM spegazzinine, a concentration of alkaloid that completely inhibited phosphorylation. However, higher concentrations of spegazzinine did partially inhibit it. The ATPase activities of submitochondrial particles, insoluble and soluble ATPases were also partially inhibited by high concentrations of spegazzinine.The inhibitory properties of spegazzinine on energy transfer reactions are compared with those of oligomycin, aurovertin and dicyclohexylcarbodiimide. It is concluded that spegazzinine effects are very similar to the effects of aurovertin and that its site of action may be the same or near the site of aurovertin.  相似文献   

18.
A Cl-stimulated ATPase activity, which is sensitive to both thiocyanate and vanadate, has been localized to the plasma membrane of Aplysia enterocytes. Utilizing plasma membrane vesicles from Aplysia enterocytes, ATP stimulated Cl uptake to approximately 2.5-times that of control in a Na+, K+ and HCO3-free medium. This ATP-dependent Cl uptake was sensitive to both thiocyanate and vanadate. These results are consistent with the hypothesis that the active Cl absorptive process in Aplysia intestine could be a Cl-stimulated ATPase found in the enterocyte plasma membrane.  相似文献   

19.
The effects of calmodulin (CaM) on ATPase activity and ATP-dependent formation of a proton gradient (ΔpH) were studied in tonoplast membrane vesicles from corn (Zea mays L.) roots. At 0.6 micromolar, CaM stimulated ATPase activity by about 20% in the absence of an uncoupler, but by only 4% in its presence. Thus, the uncoupler-dependent increment of activity was decreased 30 to 45% by CaM. The formation of a proton gradient across the membrane vesicle, measured by quinacrine fluorescence quench, was inhibited about 20% by CaM. Its effect was additive to the effect of Ca2+ and was completely abolished by EGTA. These effects of CaM could be due to stimulation of H+ efflux or due to inhibition of the H+-ATPase. To distinguish between these possibilities, we examined the effect of CaM on dissipation of preformed ΔpH after the ATPase was inhibited. CaM stimulated the dissipation of a preformed ΔpH by 40% after the H+-ATPase was inhibited with NO3. This indicates that CaM facilitates the recycling of protons across the tonoplast membranes and does not regulate the H+-ATPase by direct inhibition.  相似文献   

20.
The effect of varied Zn supply on the pH of the nutrient solution and uptake of cations and anions was studied in cotton (Gossypium hirsutum L.), sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants grown under controlled environmental conditions in nutrient solutions with nitrate as source of nitrogen. With the appearance of visual Zn deficiency symtoms, the pH of the nutrient solutions decreased from 6 to about 5 whereas the pH increased to about 7 when the plants were adequately supplied with Zn. In Zn deficient plants the pH decrease was associated with a shift in the cation-anion uptake ratio in favour of cation uptake. Of the major ions, uptake of Ca2+ and K+ was either not affected or only slightly lowered whereas NO3 - uptake was drastically decreased in Zn deficient plants. Although the Zn nutritional status of plants hardly affected the NO3 - concentrations in the plants, the leakage of NO3 - from roots of Zn deficient plants into a diluted CaCl2 solution was nearly 10 times higher than that of plants adequately supplied with Zn. In contrast to Zn deficiency, Mn deficiency in cotton plants neither affected NO3 - uptake nor the pH of the nutrient solution.The results indicate that, probably as a consequence of the role of Zn in plasma membrane integrity and nitrogen metabolism, when Zn is deficient in dicotyledonous species net uptake of NO3 - is particularly depressed which in turn results in an increase in cation-anion uptake ratio and a corresponding decrease in external pH. The ecological relevance of this rhizosphere acidification is discussed.  相似文献   

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