Indolacetic and humic acids induce lateral root development through a concerted plasmalemma and tonoplast H<Superscript>+</Superscript> pumps activation

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and humic acids (HA) isolated from two different soils (Inseptsol and Ultisol) and two different organic residues (vermicompost and sewage sludge) on root development and on activities of plasmalemma and tonoplast H⁺ pumps from maize roots. The data show that HA isolated from these different sources as well as low IAA concentrations (10⁻¹⁰ and 10⁻¹⁵ M) improve root growth through a markedly proliferation of lateral roots along with a differential activation not only of the plasmalemma but also of vacuolar H⁺-ATPases and H⁺-pyrophosphatase. Further, the vacuolar H⁺-ATPase had a peak of stimulation in a range from 10⁻⁸ to 10⁻¹⁰ M IAA, whereas the H⁺-pyrophosphatase was sensitive to a much broader range of IAA concentrations from 10⁻³ to 10⁻¹⁵ M. It is proposed a complementary view of the acid growth mechanism in which a concerted activation of the plasmalemma and tonoplast H⁺ pumps plays a key role in the root cell expansion process driven by environment-derived molecules endowed with auxinic activity, such as that of humic substances.     

Effect of melafen on the function of endoplasmic reticulum and plasmalemmal H<Superscript>+</Superscript>-atpase in the regulation of growth processes in potato tubers

The mechanism of the stimulatory effect of melafen on potato tuber sprouting was studied. The treatment with 10^?8 M melafen intensified division and stretching and activated granular endoplasmic reticulum of apical meristem cells. An increase in the activity of membrane-bound H⁺-ATPase in the plasmalemma of parenchymal cells of melafen-treated potato tubers and enhancement of passive proton permeability of the plasmalemma was observed. In vitro studies showed that melafen at concentrations of 10^?5?10^?12 M stimulated the activity of plasmalemmal H⁺-ATPase in a concentration-dependent manner.     

Melafen effect on ATP-dependent accumulation of calcium in plasma membrane vesicles from cells of potato tubers

Synthetic growth regulator melafen (10⁻⁵–10⁻¹⁰ M) was tested for aneffect on the Ca²⁺ accumulation in plasma membrane vesicles (PMVs) isolated from potato Solanum tuberosum L. tubers at forced rest and sprouting. Melafen proved to regulate the Ca²⁺ accumulation in PMVs by changing the activity of Ca²⁺, Mg²⁺-ATPase of the plasma membrane, while no effect was observed with respect to Ca²⁺ outflow from vesicles. The melafen effect on Ca²⁺, Mg²⁺-ATPase activity depended on the physiological condition of tubers and the melafen concentration.     

Effect of jasmonic acid on Ca<Superscript>+2</Superscript> transport through the plasmalemma of potato tuber cells

The rate of Ca²⁺ accumulation in plasmalemma vesicles isolated from quiescent and sprouting potato (Solanum tuberosum L.) tubers and the effect of 10^?5–10^?10 M jasmonic acid on the accumulation of Ca⁺² in plasmalemma vesicles and its efflux were studied. It was found that potato tuber plasmalemma contains a Ca⁺²,Mg⁺²-ATPase whose activity decreases upon the transition from forced quiescence to growth. The direction of the effect of jasmonic acid on Ca⁺²,Mg⁺²-ATPase (stimulation or suppression) depends on the physiological state of tubers and the phytohormone concentration.     

The effect of melamine salt of bis(oxymethyl)phosphinic acid (melafen) on the growth processes and plasma membrane function in potato tuber cells

The effects of a new synthetic growth regulator, preparation melafen, on the growth processes in potato plant tubers and the H⁺-ATPase activity in cell plasmalemma were studied. It was demonstrated that melafen could both stimulate and inhibit the growth of potato tubers depending on its concentration and the physiological state of the tubers. It is likely that one of the manifestations of melafen action is its influence on the division and extension of apical meristem cells. The growth stimulation caused by melafen is connected with modifications of the plasmalemma of potato tuber cells, namely, the activation of H⁺-ATPase and increase in the membrane proton permeability.     

The effect of thaumatin gene overexpression on the properties of H+-ATPase from the plasmalemma of potato tuber cells

The introduction of the thaumatin gene into potato plants was accompanied by a decrease in the activity of H⁺-ATPase in the plasmalemma (PL) of tuber cells. When tubers were released from dormancy, the enzyme was activated in the tuber cells of both the original and transgenic plants. Experiments performed in vitro demonstrated that sensitivities to ambiol (AM) and jasmonic acid (JA) of H⁺-ATPase in the PL of tubers from the original plants were lower after the release from a period of deep dormancy. In preparations from the tubers of transgenic plants, the situation was reversed. The differences between the activities of H⁺-ATPase in the PL preparations produced from the original and transgenic tubers that sprouted under the action of AM and JA were detected. Thus, the overexpression of the thaumatin gene in potato plants changed the properties of H⁺-ATPase from PL.     

Effects of cortisol and fluoride on ion-transporting ATPase activities in cultured osteoblastlike cells

Summary Na⁺,K⁺-ATPase, HCO ₃ ⁻ -ATPase, Ca²⁺,Mg²⁺,-ATPase, Ca²⁺-ATPase, and alkaline phosphatase activities were measured in cultures of osteoblastlike cells treated with fluoride and cortisol separately and in combinations. Low concentrations of cortisol increased HCO ₃ ⁻ -ATPase (10⁻¹¹ to 10⁻¹⁸ M cortisol) and alkaline phosphatase (10⁻¹¹ to 10⁻⁹ M cortisol) activities, but higher cortisol concentrations reduced these activities. Na⁺,K⁺-ATPase, Ca²⁺,Mg²⁺-ATPase, and Ca²⁺-ATPase activities tended only to be reduced by cortisol. Fluoride (10⁻⁶ and 5×10⁻⁶ M) increased HCO ₃ ⁻ -ATPase and alkaline phosphatase activities, but these activities were similar to controls in the presence of 10⁻⁵ M fluoride. Ca²⁺,Mg²⁺-ATPase activity was decreased and Na⁺,K⁺-ATPase activity was increased as the concentration of fluoride increased (10⁻⁶ to 10⁻⁵ M). Preliminary experiments with fluoride indicated that lower concentrations (10⁻⁷ M) were without effect. Cortisol concentrations of 10⁻⁹ and 10⁻⁸ M were chosen for studies with combinations of cortisol and fluoride because the effects of these concentrations on alkaline phosphatase activity were opposite, i.e. 10⁻⁹ M increased whereas 10⁻⁸ M decreased activity. Fluoride concentrations of 10⁻⁶, 5×10⁻⁶, and 10⁻⁵ M were chosen because a peak of alkaline phosphatase activity occurred at 5×10⁻⁶ M fluoride. Higher (10⁻⁴ M) and lower (10⁻⁷ M) fluoride concentrations were without effect. The effects of combinations of cortisol and fluoride depend on the enzyme activity measured. Fluoride (10⁻⁶ M) combined with cortisol (10⁻⁹ M) produced a peak of Na⁺,K⁺-ATPase activity. The increased activity obtained with all concentrations of fluoride alone was preserved when fluoride was combined with 10⁻⁸ M cortisol, although the activity tended to be reduced at 5×10⁻⁶ and 10⁻⁵ M fluoride. HCO ₃ ⁻ -ATPase activity was increased by fluoride combined with 10⁻⁸ M cortisol and decreased by fluoride combined with 10⁻⁹ M cortisol compared to the activities obtained with fluoride alone. The decrease in Ca²⁺,Mg²⁺-ATPase activity caused by fluoride alone was prevented by 10⁻⁹ and enhanced by 10⁻⁸ M cortisol, although all treatments produced the same activity at 10⁻⁵ M fluoride. Ca²⁺-ATPase activity tended to be increased by combinations of fluoride and cortisol, but significantly so only at 10⁻⁵ M fluoride in combinations with 10⁻⁸ and 10⁻⁹ M cortisol. Alkaline phosphatase activity was increased by fluoride combined with 10⁻⁹ M cortisol and decreased by fluoride combined with 10⁻⁸ M cortisol compared to the activities obtained with fluoride alone. These results suggest that the abilities of bone cells to regulate ion transport (as reflected in their ion-transporting ATPase activities) are modulated by glucocorticoids and fluoride. Inasmuch as these cells may regulate the ionic composition and concentrations of the bone extracellular fluid (ECF) in vivo, the modulation of their activities by cortisol and fluoride may result in altered bone ECF composition. This work was supported by Grant NAG-2-108 from the National Aeronautics and Space Administration, D.C., and Grant PO1 NS15767 from the National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, MD.     

Short-and long-term effects of cadmium on transmembrane electric potential (E m) in maize roots

In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (E _m) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 μM to 1 mM) for several hours to one week were studied. The E _m values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization was concentration-dependent reaching the value of diffusion potential (E _D) when the Cd concentration exceeded 100 μM. The values of E _D ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of E _m was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 μM) or complete repolarization (Cd < 100 μM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly after the maximum repolarization of E _m a continuous concentration-dependent decrease of E _m followed at all Cd concentrations. Depolarization of E _m was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 μM to 1 mM Cd, with the exception of root cells treated with 1 and 10 μM Cd for 24 and 48 h. Time course analysis of Cd impact on root respiration revealed that at higher Cd concentrations (> 50 μM) the respiration gradually declined (∼ 6 h) and then remained at this lowest level for up to 24 h. All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher than 100 μM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible changes in the electrogenic plasma membrane H⁺ ATPase because fusicoccin, an H⁺ ATPase activator diminished the depolarizing effect of Cd on the E _m. The depolarization of E _m in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability, and activity of H⁺ ATPase.     

灵武长枣果实质膜和液泡膜H~+-ATPase和H~+-PPase活性与果实糖分积累

以不同发育时期灵武长枣(Ziziphus jujuba cv.Lingwuchangzao)的果实为材料,通过测定与分析果肉组织中细胞质膜、液泡膜H+-ATPase和H+-PPase活性、果实糖分含量变化,研究了灵武长枣果实质膜、液泡膜H+-ATPase和H+-PPase活性与糖积累特性的关系。结果表明:(1)果实第二次快速生长期之前主要积累葡萄糖和果糖,之后果实迅速积累蔗糖,葡萄糖和果糖含量则逐渐下降,成熟期果实主要积累蔗糖。(2)在果实发育的缓慢生长期S1,质膜H+-ATPase活性最低;第一次快速生长期,质膜H+-ATPase活性最高;缓慢生长期S2,其活性降低;第二次快速生长期,质膜H+-ATPase活性升至次高;完熟期,质膜H+-ATPase活性下降幅度较大。(3)在果实发育过程中,液泡膜H+-ATPase和H+-PPase活性的变化趋势相似。缓慢生长期S1,液泡膜H+-ATPase和H+-PPase活性较低;从缓慢生长期S1至第一次快速生长期缓慢下降至最低;从第一次快速生长期开始,液泡膜H+-ATPase和H+-PPase活性呈现为逐渐增高的变化趋势;除第二次快速生长期以外,液泡膜H+-PPase活性始终高于H+-ATPase。由此推测,质膜H+-ATPase和液泡膜H+-ATPase、H+-PPase对灵武长枣果实糖分的跨膜次级转运起到重要的调控作用。     

Response of the plant root to aluminum stress: Analysis of the inhibition of the root elongation and changes in membrane function

Pea root elongation was strongly inhibited in the presence of a low concentration of Al (5 μM). In Al-treated root, the epidermis was markedly injured and characterized by an irregular layer of cells of the root surface. Approximately 30% of total absorbed Al accumulated in the root tip and Al therein was found to cause the inhibition of whole root elongation. Increasing concentrations of Ca²⁺ effectively ameliorated the inhibition of root elongation by Al and 1 mM of CaCl₂ completely repressed the inhibition of root elongation by 50 μM Al. The ameliorating effect of Ca²⁺ was due to the reduction of Al uptake. H⁺-ATPase and H⁺-PPase activity as well as ATP and PPidependent H⁺ transport activity of vacuolar membrane vesicles prepared from barley roots increased to a similar extent by the treatment with 50 μM AlCl₃. The rate of increase of the amount of H⁺-ATPase and H⁺-PPase was proportional to that of protein content measured by immunoblot analysis with antibodies against the catalytic subunit of the vacuolar H⁺-ATPase and H⁺-PPase of mung bean. The increase of both activities was discussed in relation to the physiological tolerance mechanism of barley root against Al stress.     

Possible Regulatory Effect of Lipid Peroxidation on the H+-ATPase Activity of the Plasmalemma under Stress Conditions

We studied the effects of high temperature and paraquat on the rate of lipid peroxidation and activity of the H⁺-ATPase in the plasmalemma fraction isolated from pea leaves. We demonstrated a heat-induced increase in both indices. When lipid-peroxidation was inhibited by pretreatment with butylated hydroxytoluene, a synthetic antioxidant, the H⁺-ATPase activity increased to a lesser extent than after heat shock without pretreatment. Treatment of plants with paraquat, a prooxidant causing an oxidative stress, resulted in a dramatic increase in lipid peroxidation and H⁺-ATPase activity. We suggested that the enhanced lipid peroxidation could be one of the causes for the H⁺-ATPase activation in the plasmalemma under stress conditions.     

Salicylic acid mitigates salinity stress by improving antioxidant defence system and enhances vincristine and vinblastine alkaloids production in periwinkle [<Emphasis Type="Italic">Catharanthus roseus</Emphasis> (L.) G. Don]

A pot experiment was conducted to find out whether the foliar spray of salicylic acid (SA) could successfully ameliorate the adverse effects of salinity stress on periwinkle. Thirty-day-old plants were supplied with Control; 0 mM NaCl + 10⁻⁵ M SA (T₁); 50 mM NaCl + 0 SA (T₂); 100 mM NaCl + 0 SA (T₃); 150 mM NaCl + 0 SA (T₄); 50 mM NaCl + 10⁻⁵ M SA (T₅); 100 mM NaCl + 10⁻⁵ M SA (T₆); 150 mM NaCl + 10⁻⁵ M SA (T₇). The plants were sampled 90 days after sowing to assess the effect of SA on stressed and unstressed plants. Salt stress significantly reduced the growth attributes including plant height, leaf-area index, shoot and root fresh weights, shoot and root dry weights. Increasing NaCl concentrations led to a gradual decrease in photosynthetic parameters and activities of nitrate reductase and carbonic anhydrase. Ascorbic acid, total alkaloids and antioxidants enzymes superoxide dismutase, catalase and peroxidase also declined in NaCl-treated plants. The plants, undergoing NaCl stress, exhibited a significant increase in electrolyte leakage and proline content. Foliar application of SA (10⁻⁵ M) reduced the damaging effect of salinity on plant growth and accelerated the restoration of growth processes. It not only improved the growth parameters but also reversed the effects of salinity. Total alkaloid content was improved by SA application both in unstressed and stressed plants. The highest level of total alkaloid content recorded in leaves of SA-treated stressed plants was 11.1%. Foliar spray of SA overcame the adverse effect of salinity by improving the content of vincristine (14.0%) and vinblastine (14.6%) in plants treated with 100 M NaCl.     

Immunocytochemical localization of H+?K+-ATPase in the rat colon

Summary The presence and distribution of gastric-type H⁺−K⁺-ATPase were investigated in the rat colon using a monoclonal antibody raised against hog gastric H⁺−K⁺-ATPase. Rat stomach was used as positive control. Rat kidney and ileum, in both of which H⁺−K⁺-ATPase has been reported in the past, were also studied. In stomach, very strong staining was found confined to the parietal cells, and a strong band atM _r∼94 kDa on the immunoblots. In colon a moderate staining was found in the supranuclear region of the epithelial cells, with similar intensity and distribution of staining of the surface and deep mucosa of the crypts, throughout the length of the colon. Another monoclonal antibody, specific to the 31 kDa subunit of H⁺-ATPase, used as a negative control, or omission of the primary antibody, resulted in lack of any staining in either colon or stomach. On immunoblots of homogenates of colonic mucosa, no specific band could be identified, either due to very low expression of the H⁺−K⁺-ATPase or loss of antigenicity of the epitope during the processing steps. No positive staining was observed in rat kidney and ileum, suggesting that they contain isoforms that are structurally different.     

Separate Determination of the Electrical Properties of the Tonoplast and the Plasmalemma of the Giant-Celled Alga Valonia utricularis: Vacuolar Perfusion of Turgescent Cells with Nystatin and Other Agents

In the giant-celled marine algae Valonia utricularis the turgor-sensing mechanism of the plasmalemma and the role of the tonoplast in turgor regulation is unknown because of the lack of solid data about the individual electrical properties of the plasmalemma and the vacuolar membrane. For this reason, a vacuolar perfusion technique was developed that allowed controlled manipulation of the vacuolar sap under turgescent conditions (up to about 0.3 MPa). Charge-pulse relaxation studies on vacuolarly perfused cells at different turgor pressure values showed that the area-specific resistance of the total membrane barrier (tonoplast and plasmalemma) exhibited a similar dependence on turgor pressure as reported in the literature for nonperfused cells: the resistance assumed a minimum value at the physiological turgor pressure of about 0.1 MPa. The agreement of the data suggested that the perfusion process did not alter the transport properties of the membrane barrier. Addition of 16 μm of the H⁺-carrier FCCP (carbonylcyanide p-trifluoromethoxyphenyhydrazone) to the perfusion solution resulted in a drop of the total membrane potential from +4 mV to −22 mV and in an increase of the area-specific membrane resistance from 6.8 × 10⁻² to 40.6 × 10⁻²Ωm². The time constants of the two exponentials of the charge pulse relaxation spectrum increased significantly. These results are inconsistent with the assumption of a high-conductance state of the tonoplast (R. Lainson and C.P. Field, J. Membrane Biol. 29:81–94, 1976). Depending on the site of addition, the pore-forming antibiotics nystatin and amphotericin B affected either the time constant of the fast or of the slow relaxation (provided that the composition of the perfusion solution and the artificial sea water were replaced by a cytoplasma-analogous medium). When 50 μm of the antibiotics were added externally, the fast relaxation process disappeared. Contrastingly, the slow relaxation process disappeared upon vacuolar addition. The antibiotics cannot penetrate biomembranes rapidly, and therefore, the findings suggested that the fast and slow relaxations originated exclusively from the electrical properties of the plasmalemma and the tonoplast respectively. This interpretation implies that the area-specific resistance of the tonoplast is significantly larger than that of the plasmalemma (consistent with the FCCP data) and that the area-specific capacitance of the tonoplast is unusually high (6.21 × 10⁻² Fm⁻² compared to 0.77 × 10⁻² Fm⁻² of the plasmalemma). Thus, we have to assume that the vacuolar membrane of V. utricularis is highly folded (by a factor of about 9 in relation to the geometric area) and/or contains a fairly high concentration of mobile charges of an unknown electrogenic ion carrier system. Received: 22 October 1996/Revised: 16 January 1997     

Effects of salt-adaptation and salt-stress on extracellular acidification and microsome phosphohydrolase activities in tomato cell suspensions

The effects of NaCl-adaptation and NaCl-stress on in vivo H⁺ extrusion and microsomal vanadate- and bafilomycin-sensitive ATPase and PPase activities were studied in tomato cell suspensions. Acidification of the external medium by 50 mM NaCl-adapted and non-adapted (control) tomato cells was similar. Extracellular acidification by both types of cells during the first hour of incubation with 2 μM fusicoccin (FC) in the presence of 100 mM NaCl was lightly increased while in the presence of 100 mM KCl it was increased by 3 (control)- and 6.5 (adapted)-fold. Extracellular alkalinization after 2 h of cell incubation in 100 mM NaCl indicated the possibility that a Na⁺/H⁺ exchange activity could be operating in both types of cells. Moreover, acidification induced by adding 100 mM NaCl + FC to non-adapted cells was relatively less affected by vanadate than that induced by 5 mM KCl + FC, which suggested that salt stress could induce some component other than H⁺ extrusion by H⁺-ATPase. In addition, no differences were observed in microsomal vanadate-sensitive ATPase activity among control, NaCl-adapted and NaCl-stressed cells, while K⁺-stimulated H⁺-PPase and bafilomycin-sensitive H⁺-ATPase activities were higher in microsomes from NaCl-adapted than in those from control cells. Likewise, the stimulation of in vivo H⁺ extrusion in NaCl adapted cells under NaCl or KCl stress in the presence of FC occurred with an inhibition of H⁺-PPase and bafilomycin-sensitive H⁺-ATPase activities and without changes in the vanadate-sensitive H⁺-ATPase activity. These results suggest that the stimulation of tonoplast proton pumps in NaCl-adapted cells, without changes in plasmalemma H⁺-ATPase, could serve to energize Na⁺ efflux across the plasmalemma and Na⁺ fluxes into vacuoles catalyzed by the Na⁺/H⁺ antiports. This revised version was published online in June 2006 with corrections to the Cover Date.     

Salicylic acid can regulate phloem unloading in the root tip

In three-day-old maize (Zea mays L.) seedlings, we removed the endosperm, coleoptile with leaflets, and adventitious roots. Primary roots were exposed to 0–10⁻³ M salicylic acid (SA) for 1–5 h; scutellum, to 10⁻² M 2-desoxy-D-glucose (2dG). 2dG-sucrose synthesized from 2dG was transported from scutella to the roots along the phloem. Its accumulation in 5-mm-long root tips was the measure of phloem unloading. At the concentrations higher than 10⁻⁴ M, SA suppressed unloading. Simultaneously, the uptake of ¹⁴C-5,5-dimethyloxazolidinedione (DMO) by root segments was inhibited, indicating cytoplasm acidification. 10⁻³ M SA also inhibited root respiration and growth. The lower SA concentrations (10⁻⁵ and 10⁻⁶ M) activated unloading under conditions of weak sucrose phloem transport to the root. They did not affect DMO uptake, respiration, and growth. 10⁻⁴ M SA stimulated unloading during 1- or 2-h exposure but did not affect it at longer treatments. A dependence of SA action on its concentration and exposure duration implies its involvement in the control of phloem unloading in the root tip.     

Alteration of transport activity of proton pumps in coleoptile cells during early development stages of maize seedlings

Comparative analysis of the transport activity of proton pumps (plasmalemma H⁺-ATPase, vacuolar H⁺-ATPase, and vacuolar H⁺-pyrophosphatase) in the membrane preparations obtained from coleoptile cells of etiolated maize seedlings (Zea mays L.) was carried out. The highest level of vacuolar pyrophosphatase activity was observed during the early development of coleoptile cells under growth intensification through the elongation. The role of ATPase pumps of tonoplast and plasmalemma in the transport of hydrogen ions increases during further development. The plasmalemma activity in this process is higher. When the growth stops, the activity of proton pumps becomes significantly lower. Nevertheless, their substrate specificity and sensitivity to proton pump inhibitors do not change, which can be an evidence of physiological significance of pumps in the maintenance of cell homeostasis.     

In vivo and in vitro effects of copper and cadmium on the plasma membrane H+-ATPase from cucumber (Cucumis sativus L.) and maize (Zea mays L.) roots

The plasmalemma vesicles isolated from cucumber and maize roots were used to study the effect of Cu²⁺ and Cd²⁺ on the hydrolytic and proton pumping activities of ATPase. In vivo application of metal ions to the plant growth solutions resulted in stimulation of the proton transport in maize. In cucumber roots the action of metals was not the same: cadmium stimulated the H⁺ transport through plasmalemma whereas Cu²⁺ almost completely inhibited it. Copper ions decreased the hydrolytic activity of H⁺-ATPase in cucumber, without any effect on this activity in membranes isolated from maize roots. The effect of cadmium on the hydrolytic activities was opposite: ATP-hydrolysis activity in plasmalemma was not altered in cucumber, whereas in maize its stimulation was observed. The amount of accumulated metals was not the main reason of different influence of metals on H⁺-ATPase activity in tested plants. In in vitro experiments Cu²⁺ inhibited H⁺ transport in the cucumber, to a higher degree than Cd²⁺ and both metals did not change this H⁺-ATPase activity of plasmalemma isolated from corn roots. Cu²⁺ added into the incubation medium reduced the hydrolytic activity of ATPase in the plasma membrane isolated from cucumber as well as from corn roots. Cd²⁺ diminished the hydrolytic activity of ATPase in cucumber, and no effect of Cd²⁺ in the plasmalemma isolated from corn roots was found. Our results indicated different in vitro and in vivo action of both metals on H⁺-ATPase and different response of this enzyme to Cu²⁺ and Cd²⁺ in maize and cucumber.