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1.
It has recently been reported that plasmalemma electron transport may be involved in the generation of H + gradients and the uptake of ions into root tissue. We report here on the influence of extracellular NADH and ferricyanide on K + ( 86Rb +) influx, K + ( 86Rb +) efflux, net apparent H + efflux, and O 2 consumption in 2-centimeter corn ( Zea mays [A632 × Oh43]) root segments and intact corn roots. In freshly excised root segments, NADH had no effect on O 2 consumption and K + uptake. However, after the root segments were given a 4-hour wash in aerated salt solution, NADH elicited a moderate stimulation in O 2 consumption but caused a dramatic inhibition of K + influx. Moreover, net apparent H + efflux was significantly inhibited following NADH exposure in 4-hour washed root segments. Exogenous ferricyanide inhibited K+ influx in a similar fashion to that caused by NADH, but caused a moderate stimulation of net H+ efflux. Additionally, both reagents substantially altered K+ efflux at both the plasmalemma and tonoplast. These complex results do not lend themselves to straightforward interpretation and are in contradiction with previously published results. They suggest that the interaction between cell surface redox reactions and membrane transport are more complex than previously considered. Indeed, more than one electron transport system may operate in the plasmalemma to influence, or regulate, a number of transport functions and other cellular processes. The results presented here suggest that plasmalemma redox reactions may be involved in the regulation of ion uptake and the `wound response' exhibited by corn roots. 相似文献
2.
Absorption characteristics of Mg 2+ and Cl − were investigated with 5-day-old excised corn ( Zea mays) roots. Uptake from both 0.5 and 10 milliequivalents per liter MgCl 2 solutions occurred at steady state rates for the first 6 hours. Inhibition by dinitrophenol and low temperatures established that absorption during this period was metabolically mediated in the absence and presence of Ca 2+. Absorption isotherms indicated dual mechanisms of Mg 2+ and Cl − absorption from solutions above 1 milliequivalent per liter. The effect of H + on absorption of Mg 2+ and Cl − was typical of that generally reported for other plant roots and other ions. In the physiological pH range, Ca 2+ greatly suppressed the rate of Mg 2+ absorption but had little effect on Cl −. The influence of Ca 2+ on Mg 2+ appeared to be noncompetitive and independent of its effect on membrane permeability. 相似文献
3.
Excised barley roots accumulated 40 to 50% more K + from 0.04 m m than from 0.06 m m KCl when incubated for 24 hours in KCl solutions containing 0.2 m m CaSO 4. This phenomenon was not markedly influenced by the rate of absorption of the counteranion. The presence of Na + in the treatment solutions decreased total K accumulation but did not alter the K + concentration at which the accumulation peak occurred. Short interval studies indicated that this phenomenon is easily observable after 4 hours and begins to become apparent within 2 hours. In comparison with barley, accumulation of K + by excised wheat roots decreased as KCl concentration was increased from 0.02 to 0.06 m m; but K + accumulation curve for corn roots showed no peaks or depressions in the concentration range of 0.01 to 0.1 m m. A normal hyperbolic curve was noted for the accumulation of Na + from 0.01 to 1 m m NaCl by barley roots. 相似文献
4.
Effects of 2,4-dinitrophenol (DNP) and several other substituted phenols on permeability of barley roots ( Hordeum vulgare var. Trebi) to ions were assayed as a function of pH and phenol concentration. Solutions containing 0.1 micromolar undissociated DNP increase the permeability of barley root cells to small ions such as K +, Na +, Ca 2+, and Cl − with no inhibition of respiration. Undissociated forms of the other phenols increase permeability also, but they are less effective than DNP. Only the undissociated DNP is effective. Anionic DNP does not increase permeability or inhibit ion uptake, although it is the major species accumulated by the roots, both at pH 5 and pH 7. At pH 7, in contrast to pH 5, 10 micromolar DNP has no effect on ion permeability of barley roots yet it uncouples oxidative phosphorylation of barley root mitochondria. This indicates that the all too common use of DNP as a test for active transport or involvement of ATP synthesis can be misleading. 相似文献
5.
The effects of monovalent cations, inhibitors of metabolism dinitrophenol (DNP), carbonyl cyanide- p-trifluoromethoxyphenylhydrazone (FCCP), and KCN and temperature variations upon Ca 2+ fluxes in intact roots of barley ( Hordeum vulgare L. cv. Fergus and Herta) seedlings were investigated. 45Ca 2+ influx was depressed in CaSO 4-grown (low-salt) plants by the presence of NH 4+, K +, or Na + in the uptake medium. In contrast Ca 2+ influx was slightly increased by Li +. In low-salt roots pretreated with KCN and in roots preloaded with K + (high-K + plants), the presence of K + in the medium had no significant effect on Ca 2+ influx, while in roots preloaded with Na +, the presence of K + in the medium depressed Ca 2+ influx. In absolute terms, Ca 2+ influx was significantly greater in high-salt (both K + or Na + preloaded) than in low-salt roots.Patterns of 45Ca 2+ efflux in the absence and in the presence of K +, NH 4+, or Li + in the external medium showed that these monovalent cations caused stimulation of 45Ca 2+ efflux both from the cytoplasmic and vacuolar phases.It was noted that these modifications of Ca 2+ fluxes by monovalent cations are transient and characteristic of a transitional stage of cation uptake by low-salt roots. We conclude that, together with stimulated active H + efflux (another characteristic of this transitional stage), modifications of Ca 2+ fluxes during monovalent cation uptake by low-salt roots is a response directed towards the maintenance of electrical neutrality.Determination of net fluxes revealed that the plants were close to Ca 2+ flux equilibrium in the growth medium (0.5 mM CaSO 4). Transfer of these plants to 0.5 mM CaSO 4 + 0.25 mM K 2SO 4 caused a net release of CA 2+ into the external medium. 相似文献
6.
The absorption of K + by excised roots of barley ( Hordeum vulgare L. cv California Mariout) has been systematically compared with that of entire, undisturbed seedlings. Some experiments have also been done with wheat ( Triticum aestivum L.) and an amphiploid obtained from a cross between it and salt-tolerant tall wheatgrass ( Lophopyrum elongatum Host Löve [syn. Agropyron elongatum Host]). For all three genotypes, the rate of K + absorption measured in a 20-min period was identical for entire 8-d-old seedlings and their excised roots within the experimental error. Manipulation gentler than root excision, viz. careful transfer of seedlings from one experimental solution to another, was also without effect on the rate of K + absorption. Absorption of K + measured by assay of its 86Rb label in the tissue was identical with that measured by K + depletion of the experimental solutions assayed chemically. For the plant materials and conditions of these experiments, the excised root technique for studying ion transport into roots is validated. The advantages of the technique, and findings differing from the present ones, are discussed. 相似文献
7.
Washing corn ( Zea mays L.) root tissue in water causes loss of about one-third of the exchangeable Ca 2+ over the first 10 to 15 minutes. Upon transfer to K +-containing solutions, the tissue shows a short period of rapid K + influx which subsequently declines. Addition of 0.1 millimolar Ca 2+ decreases the initial rapid K + influx, but increases the sustained rate of K + and Cl − uptake. It was confirmed (Elzam and Hodges 1967 Plant Physiol 42: 1483-1488) that 0.1 millimolar Ca 2+ is more effective than higher concentrations for the initial inhibition, and that Mg 2+ will substitute. The inhibition arises from a mild shock affect of restoring Ca2+. With 0.1 millimolar Ca2+ net H+ efflux is blocked for 10 to 15 minutes and the cells are depolarized by about 30 millivolts. However, 1 millimolar Ca2+ rapidly produces increased K+ influx and blocks net H+ efflux for only a few minutes; blockage is preceded by a brief net H+ influx which may restore and increase ion transport by reactivating the plasmalemma H+-ATPase. Stimulation of electrogenic H+-pumping with fusicoccin eliminates the shock responses and minimizes Ca2+ effects on K+ influx. Fusicoccin also strongly decreases Ca2+ influx, but has no effect on Ca2+ efflux. Ice temperatures and high pH decreased Ca2+ efflux, but uncoupler and chlorpromazine did not. It is suggested that the inhibitory and promotive actions of Ca2+ are manifested through decreases or increases in the protonmotive force. 相似文献
8.
Summary Chloride absorption by excised barley roots from dilute solutions is more oligomycin-sensitive than its absorption from more concentrated solutions and than K + and Na + absorption from dilute as well as concentrated solutions. Oligomycin decreased the ATP content of excised barley roots. The mode of oligomycin interference with ion absorption by plant cells is discussed. 相似文献
9.
We have investigated the effects of hyperpolarization and depolarization, and the presence of K + and/or Ca 2+, on 22Na + influx into corn ( Zea mays L.) root segments. In freshly excised root tissue which is injured, Na + influx is unaffected by hyperpolarization with fusicoccin, or depolarization with uncoupler (protonophore), or by addition of K +. However, added Ca 2+ suppresses Na + influx by 60%. In washed tissue which has recovered, Na + influx is doubled over that of freshly excised tissue, and the influx is increased by fusicoccin and suppressed by uncoupler. This energy-linked component of Na + influx is completely eliminated by low concentrations of K +, leaving the same level and kind of Na + influx seen in freshly excised roots. The K +-sensitive energy linkage appears to be by the carrier for active K + influx. Calcium is equally inhibitory to Na + influx in washed as in fresh tissue. Other divalent cations are only slightly less effective. Net Na + uptake was about 25% of 22Na + influx, but proportionately the response to K + and Ca 2+ was about the same. The constancy of K+-insensitive Na+ influx under conditions known to hyperpolarize and depolarize suggests that if Na+ transport is by means of a voltage-sensitive channel, the rise or fall of channel resistance must be proportional to the rise or fall in potential difference. The alternative is a passive electroneutral exchange of 22Na+ for endogenous Na+. The data suggest that an inwardly directed Na+ current is largely offset by an efflux current, giving both a small net uptake and isotopic exchange. 相似文献
10.
Ca 2+ uptake was studied in short-term experiments using 5-day-old excised maize roots. This tissue readily absorbs Ca 2+, and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated. The uptake of Ca 2+, 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: NO 3− > Cl − = Br − > SO 42−. K + and H + greatly interfere with Ca 2+ absorption, while Li + and Na + have only slight effects. 相似文献
11.
The relationship of malate synthesis to K + absorption from solutions of K 2SO 4 and KHCO 3 was compared in nonvacuolate barley ( Hordeum vulgare) root tips and whole excised roots. The comparison has permitted separation of the process which evokes organic acid synthesis from that which leads to stoichiometry between net acid equivalents formed and excess K + absorbed from K 2SO 4, on the one hand, and total K + absorbed from KHCO 3, on the other. Both in tips and in roots K + uptake from 20 mN salt solution exceeds malate synthesis in the first hour. In vacuolate roots the expected stoichiometry is achieved with time. When root tips are transferred to dilute CaSO 4, malate is rapidly metabolized, and K + is lost to the solution. By contrast, in excised whole roots the malate level remains unchanged, the salt-induced organic acid presumably being retained in the vacuole. In excised roots malonate leads to a marked drop in malate levels in untreated roots as well as in roots which have experienced salt-induced net malate synthesis. In consequence, it is contended that malonate makes available normally sequestered vacuolar malate. 相似文献
12.
Our previous studies suggested the cross talk of nitric oxide (NO) with Ca 2+ in regulating stomatal movement. However, its mechanism of action is not well defined in plant roots. In this study, sodium
nitroprusside (SNP, a NO donor) showed an inhibitory effect on the growth of wheat seedling roots in a dose-dependent manner,
which was alleviated through reducing extracellular Ca 2+ concentration. Analyzing the content of Ca 2+ and K + in wheat seedling roots showed that SNP significantly promoted Ca 2+ accumulation and inhibited K + accumulation at a higher concentration of extracellular Ca 2+, but SNP promoted K + accumulation in the absence of extracellular Ca 2+. To gain further insights into Ca 2+ function in the NO-regulated growth of wheat seedling roots, we conducted the patch-clamped protoplasts of wheat seedling
roots in a whole cell configuration. In the absence of extracellular Ca 2+, NO activated inward-rectifying K + channels, but had little effects on outward-rectifying K + channels. In the presence of 2 mmol L −1 CaCl 2 in the bath solution, NO significantly activated outward-rectifying K + channels, which was partially alleviated by LaCl 3 (a Ca 2+ channel inhibitor). In contrast, 2 mmol L −1 CaCl 2 alone had little effect on inward or outward-rectifying K + channels. Thus, NO inhibits the growth of wheat seedling roots likely by promoting extracellular Ca 2+ influx excessively. The increase in cytosolic Ca 2+ appears to inhibit K + influx, promotes K + outflux across the plasma membrane, and finally reduces the content of K + in root cells. 相似文献
13.
Influx isotherms were obtained for 86Rb + uptake into 2-cm corn ( Zea mays [A632 × (C3640 × Oh43)] root segments for both low- (0.2 millimolar CaSO 4) and high-salt (0.2 millimolar CaSO 4 + 5 millimolar KCl) grown roots. Unlike the discontinuous curves usually presented for K + influx, our isotherms were smooth, nonsaturating curves that approached linearity at K + (Rb +) concentrations above 1 millimolar. The kinetics for K + transport could be resolved into saturable and linear components. The saturable components yielded Km values of 16 and 86 micromolar for low- and high-salt roots, respectively, while Vmax values were 5.62 and 1.85 moles per gram fresh weight per hour. Results of experiments with the penetrating sulfhydryl reagent, N-ethyl maleimide (NEM), and the impermeant reagent, p-chloromercuribenzene sulfonic acid (PCMBS) indicated that the saturable and linear components were independent mechanisms of K + transport. Short-term NEM exposures (30 seconds to 5 minutes) selectively inhibited the saturable system, but had little effect on the linear component. Increasing NEM exposures resulted in further inhibition and subsequent abolition of the saturable component; the linear component exhibited limited NEM sensitivity. PCMBS elicited the same general inhibitory trends, although it was less effective as a saturable component inhibitor. The effects of NEM and PCMBS on K+ efflux were also studied. Short NEM exposures had no effect on cytoplasmic efflux, while inhibiting vacuolar efflux significantly. From these data, it is unclear at which site(s) NEM is acting. A more complex response was obtained with PCMBS, where a monophasic efflux curve was observed. Analysis indicated that the vacuolar efflux was stimulated, while the cytoplasmic component was abolished. The nature of the linear component is discussed, and it is proposed that the mechanism may be more complex than simple facilitated diffusion. 相似文献
14.
研究盐胁迫下3个品种平欧杂种榛幼苗叶片解剖结构和离子代谢特征,以揭示盐胁迫响应与适应机制及不同品种的耐盐性差异。以‘达维’、‘辽榛7号’、‘玉坠’2年生压条苗为材料,在盆栽条件下经轻度、中度、重度(分别为50、100、200 mmol/L NaCl)盐胁迫处理,设对照为0,研究幼苗叶片显微解剖结构参数和Na~+、K~+、Cl~-、Ca 2+含量的变化及其在根、茎、叶中的吸收、运输和分配特征。不同品种平欧杂种榛叶片厚度、上表皮厚度、下表皮厚度、栅栏组织和海绵组织厚度随着盐胁迫程度的增强呈现出先增加后降低的特点,轻度和中度胁迫下各参数显著高于对照。中度盐胁迫显著提高了各品种叶片结构紧密度。盐胁迫导致平欧杂种榛根、茎、叶Na~+和Cl~-含量明显高于对照。盐胁迫下,Na~+和Cl~-在叶中的绝对含量明显高于茎和根,但二者的增幅以根中最大,叶中最小,表明平欧杂种榛根系首先会吸收并截留一定数量的Na~+和Cl~-,然后将其运输至茎和叶中。与对照相比,轻度和中度盐胁迫下根、茎对K~+和Ca 2+的吸收保持稳定或减少,叶对K~+和Ca 2+... 相似文献
15.
Salinization of the medium inhibits both K + uptake by excised barley ( Hordeum vulgare L.) roots and K + release from their stele, as measured by short-term 86Rb uptake and xylem exudation, respectively. Although inhibition was not specific to chloride, mannitol caused a different response from that of inorganic sodium salts, indicating that inhibition was at least partly the result of an ion effect. In roots previously exposed to low levels of NaCl, NaCl stress directly affected stelar K + release, whereas in low-sodium roots stelar K + release was much less salt-sensitive than K + uptake.Abbreviation chCl
choline chloride 相似文献
16.
Calcium has been demonstrated to ameliorate the inhibitory effects of high salinity on nutrient transport in plants. Time-course experiments were carried out to study the effect of high Ca 2+ (6 mM) supply under saline conditions (100 mM NaCl) on the regulation of intracellular pH in excised barley ( Hordeum vulgare L. cv Arivat) roots. In-vivo 31P-nuclear magnetic resonance measurements showed an alkalinization of the vacuolar pH after salt treatment. In the presence of high Ca 2+ the extent of salt-induced vacuolar alkalinization was lower. High Ca 2+ partially mitigated the salt-induced increase in Na + content and decrease in K + content of the root. The pattern of change in the vacuolar pH paralleled that of Na + accumulation in the root. This correlation is consistent with the involvement of a tonoplast Na +/H + antiporter in Na + transport and the role of Ca 2+ in Na + uptake. High salt appeared to decrease the Pi content of the vacuole while high Ca 2+ increased this content irrespective of the salt treatment.Abbreviation NMR
nuclear magnetic resonance
We are grateful to Dr. T.W.M. Fan and R.M. Highasi (University of California, Davis, USA) for their valuable help with the NMR experiments. We also thank Dr. J. Norlyn for his technical assistance. V. Martinez was supported by a Fulbright fellowship. 相似文献
17.
A detailed examination was conducted on the linear, or first-order kinetic component for K +( 86Rb +) influx into root segments of both low- and high-salt grown corn seedlings ( Zea mays [A632 × Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl − in the uptake solution by either SO 42−, H 2PO 4−, or NO 3− caused a significant (50-60%) and specific inhibition of the linear component of K + influx. The anion transport inhibitor, 4,4′-diisothiocyano-2,2′-disulfonic acid, was found to abolish saturable Cl − influx in corn roots while causing a significant (50-60%) and specific inhibition of the linear K + uptake system; this inhibition was identical to that observed when Cl − was replaced by other anions in the K + uptake solution. Additionally, the quaternary ammonium cation, tetraethylammonium, which has been shown to block K + channels in nerve axons, also caused a dramatic (70%) and specific inhibition of the linear component of K + influx, but this was obtained only in high-salt roots. The reasons for this difference are discussed with respect to the differing abilities of low- and high-salt roots to absorb tetraethylammonium. Our present results indicate that the linear component of K+ influx may occur by a passive process involving transmembrane K+ channels. Fluxes through these K+ channels may be partly coupled to a saturating Cl− influx mechanism. 相似文献
18.
Summary Plasma membrane vesicles, which are mostly right side-out, were isolated from corn leaves by aqueous two-phase partitioning method. Characteristics of Ca 2+ transport were investigated after preparing inside-out vesicles by Triton X-100 treatment. 45Ca 2+ transport was assayed by membrane filtration technique. Results showed that Ca 2+ transport into the plasma membrane vesicles was Mg-ATP dependent. The active Ca 2+ transport system had a high affinity for Ca 2+( K
m
(Ca 2+)=0.4 m) and ATP( K
m
(ATP)=3.9 m), and showed pH optimum at 7.5. ATP-dependent Ca 2+ uptake in the plasma membrane vesicles was stimulated in the presence of Cl – or NO
3
–
. Quenching of quinacrine fluorescence showed that these anions also induced H + transport into the vesicles. The Ca 2+ uptake stimulated by Cl – was dependent on the activity of H + transport into the vesicles. However, carbonylcyanide m-chlorophenylhydrazone (CCCP) and VO
4
3–
which is known to inhibit the H + pump associated with the plasma membrane, canceled almost all of the Cl –-stimulated Ca 2+ uptake. Furthermore, artificially imposed pH gradient (acid inside) caused Ca 2+ uptake into the vesicles. These results suggest that the Cl –-stimulated Ca 2+ uptake is caused by the efflux of H + from the vesicles by the operation of Ca 2+/H + antiport system in the plasma membrane. In Cl –-free medium, H + transport into the vesicles scarcely occurred and the addition of CCCP caused only a slight inhibition of the active Ca 2+ uptake into the vesicles. These results suggest that two Ca 2+ transport systems are operating in the plasma membrane from corn leaves, i.e., one is an ATP-dependent active Ca 2+ transport system (Ca 2+ pump) and the other is a Ca 2+/H + antiport system. Little difference in characteristics of Ca 2+ transport was observed between the plasma membranes isolated from etiolated and green corn leaves. 相似文献
19.
The fast-activating vacuolar (FV) channel dominates the electrical characteristics of the tonoplast at physiological free Ca 2+ concentrations. Since polyamines are known to increase in plant cells in response to stress, the regulation of FV channels by polyamines was investigated. Patch-clamp measurements were performed on whole barley ( Hordeum vulgare ) mesophyll vacuoles and on excised tonoplast patches. The trivalent polyamine spermidine and the tetravalent polyamine spermine blocked FV channels with K d≈ 100 μM and K d≈ 5 μM, respectively. Increasing cytosolic and vacuolar Ca 2+ had no effect on putrescine and spermidine binding to FV channels but slightly decreased the affinity for spermine. The inhibition of FV channels by all three polyamines was not voltage-dependent. This points to a different mode of binding compared to inward rectifier K + channels and Ca 2+-permeable glutamate receptor channels from animal cells, which show rectification due to a voltage-dependent block by polyamines. In plant cells, the common polyamines (putrescine, spermidine and spermine) are likely to mediate a salt stress-induced decrease of ion flux across the vacuolar membrane by blocking FV channels. 相似文献
20.
An ion-selective vibrating-microelectrode system, which was originally used to measure extracellular Ca 2+ gradients generated by Ca 2+ currents, was used to study K +, H + and Ca 2+ transport in intact maize ( Zea mays L.) roots and individual maize suspension cells. Comparisons were made between the vibrating ion-selective microelectrode, and a technique using stationary ion-selective microelectrodes to measure ionic gradients in the unstirred layer at the surface of plant roots. The vibrating-microelectrode system was shown to be a major improvement over stationary ion-selective microelectrodes, in terms of sensitivity and temporal resolution. With the vibrating ion microelectrode, it was easy to monitor K + influxes into maize roots in a background K + concentration of 10 mM or more, while stationary K + electrodes were limited to measurements in a background K + concentration of 0.3 mM or less. Also, with this system it was possible to conduct a detailed study of root Ca 2+ transport, which was previously not possible because of the small fluxes involved. For example, we were able to investigate the effect of the excision of maize roots on Ca 2+ influx. When an intact maize root was excised from the seedling at a position 3 cm from the site of measurement of Ca 2+ transport, a rapid fourfold stimulation of Ca 2+ influx was observed followed by dramatic oscillations in Ca 2+ flux, oscillating between Ca 2+ influx and efflux. These results clearly demonstrate that wound or perturbation responses of plant organs involve transient alterations in Ca 2+ transport, which had previously been inferred by demonstrations of touch-induced changes in cytoplasmic calcium. The sensitivity of this system allows for the measurement of ion fluxes in individual plant cells. Using vibrating K + and H +electrodes, it was possible to measure H +efflux and both K + influx and efflux in individual maize suspension cells under different conditions. The availability of this technique will greatly improve our ability to study ion transport at the cellular level, in intact plant tissues and organs, and in specialized cells, such as root hairs or guard cells.Symbol X
amplitude of vibration
The authors would like to thank Richard Sanger for his invaluable work on the design and improvement of the ion-selective vibratingmicroelectrode system. The research presented here was supported in part by U.S. Department of Agriculture Competitive Grant No. 90-37261-5411 to Leon Kochian and William Lucas. 相似文献
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