Cation uptake from bentonite suspensions by excised barley roots

Summary The net uptake of Na, K, or Ca by excised barley roots as influenced by the amount and kind of other cation was studied from bi-ionic and tri-ionic bentonite suspensions. The net uptake of Na or K from the Na-Ca or K-Ca system followed the concentration of soluble Na or K in the system. Calcium in both systems was taken up by the excised roots only at the 80 and 100 per cent Ca levels. At lower levels of Ca, the roots lost some of their initial calcium contents to the suspensions. The net uptake of Na or K from the Na-K system was in agreement with the concentrations of soluble Na or K in the system. At the various levels of Na or K, some of the initial calcium of the roots was lost to the suspensions. In the Na-K-Ca system, Na uptake gradually decreased with the increase of Ca level. Calcium was not absorbed by the roots at the various Ca levels. However, calcium greatly enhanced K uptake from this system. Part of a dissertation submitted by the senior author in partial fulfillment of requirements for the Ph. D. degree.     

Accumulation, Partitioning and Redistribution of Dry Matter and Mineral Nutrients in Ixia flexuosa L., with Special Reference to its Cormaceous Habit

The seasonal dynamics of uptake, partitioning and redistributionof dry matter, N, P, K, S, Ca, Mg, Na, Cl, Fe, Zn, Mn and Cuby the cormaceous plant Ixia flexuosa were studied in pot cultureat Perth, Western Australia. Dry matter and P, N, K, Zn andCu were redistributed from the mother corm with about 90 percent net efficiency: there was no net redistribution of Ca,Na, Fe or Mn. The efficiency of redistribution from the leafyshoot to fruits and the new season's corm was 80 per cent forN and P, 24–49 per cent for K, Cu and Zn, and 0–15per cent for Na, Fe, Ca, Mn, Cl, Mg, S and dry matter. Redistributionfrom the mother corm and vegetative organs could have suppliedthe replacement corm, cormlets and fruits with 32–53 percent of their S, K, P, N, Cu and Zn, and 11–25 per centof their Ca, Cl, Mn, Mg and dry matter. The mature replacementcorm had over 60 per cent of the plant's N and P, 25–50per cent of its dry matter, Zn, Cu, Mg, K and Cl, but less than20 per cent of its Ca, Na, Fe and Mn. Each plant produced anaverage of 12 cormlets; these had 35 per cent of the dry matterand 23–47 per cent of the amount of a particular nutrientin the new season's corms. Fruits had less than 16 per centof the dry matter and each mineral in the mature plant. Ratesof mineral intake by Ixia were much lower than reported forcrop plants, and may be related to the long growing season ofthe species. Ixia polystachya L., corm, nutrition, mineral nutrients, nutrient redistribution     

Potassium and magnesium relationship in cowpea (Vigna unguiculata (L.) Walp.)

Summary The effects of K and Mg application on dry matter yield and uptake of K, Mg and Ca in cowpea were studied in greenhouse at Haryana Agricultural University, Hissar (india). Dry matter yields of leaves, stems and roots increased by 17, 30 and 27 per cent over control due to application of 150 ppm K and 17, 16 and 26 per cent by 40 ppm Mg respectively. Potassium application has antagonistic effect on Ca concentration of leaves, stems and roots and synergistic on root Mg concentrations upto 25 ppm K. However, Mg had a synergistic effect on concentration of K upto 20 ppm Mg and antagonistic at 40 ppm Mg in all plant parts. Uptake of K, Mg and Ca increased by Mg application, but K increased only K uptake.     

Urease activity in soils

Summary The availability of Ca from different levels of gypsum and calcium carbonate in a non-saline sodic soil has been investigated. Different levels of tagged gypsum (Ca⁴⁵SO₄.2H₂O) and calcium carbonate (Ca⁴⁵CO₃) (i.e. 0, 25, 50, 75, and 100 per cent of gypsum requirement) were mixed thoroughly in 3.5 Kg of a non-saline alkali soil (ESP, 48.4; ECe, 2.68 millimhos/cm). Dhaincha (Sesbania aculeata) — a legume and barley (Hordeum vulgare L.) — a cereal were taken as test crops. Increasing levels of gypsum caused a gradual increase in the yield of dry matter, content of Ca and K in the plant tops and Ca:Na and (Ca+Mg):(Na+K) ratios in both the crops. Application of calcium carbonate caused a slight increase in the dry matter yield, content of Ca and Mg and Ca:Na and (Ca+Mg):(Na+K) ratios in barley, however, in case of dhaincha there was no such effect. Gypsum application caused a gradual decrease in the content of Na and P in both the crops. Total uptake of Ca, Mg, K, N and P per pot increased in response to gypsum application. The effect of calcium carbonate application on the total uptake of these elements was much smaller on dhaincha, but in barley there was some increasing trend.Increasing application of tagged gypsum and calcium carbonate caused a gradual increase in the concentration and per cent contribution of source Ca in both the crops, although, the rate of increase was considerably more in dhaincha. The availability of Ca from applied gypsum was considerably more than that from applied calcium carbonate. Efficiency of dhaincha to utilize Ca from applied sources was considerably more (i.e. about five times) than that of barley     

Availability of Ca from Ca45SO4 in a highly saline-sodic soil

Summary Application of gypsum (tagged Ca⁴⁵SO₄.2H₂O) caused a considerable increase in dry matter yield and content of Ca, Ca⁴⁵, Mg and K and Ca:Na and (Ca+Mg): (Na+K) ratios and a decrease in the content of Na, N and P in dhaincha tops. There was a considerable increase in the total uptake of Ca, Mg, Na, K, N, P and Ca⁴⁵ by plant tops in response to gypsum. Contribution of Ca from applied Ca⁴⁵SO₄ varied from 78.3 to 84.7 per cent of the total Ca in plant tops, whereas, its uptake from this source varied from 52.18 to 98.73 me per 100 g plant tops. re]19720705     

Effect of farm yard manure on the availability of Ca from Ca45CO3 in a sodic soil (ESP 77.7)

Summary Application of FYM caused a gradual increase in the dry weight of dhaincha (Sesbania aculeata Pers.) tops. It also caused a gradual increase in the content of Mg and K and a decrease in the content of Ca, Na, N and P in dhaincha tops. Increase in Ca: Na ratio was more steeper than (Ca+Mg): (Na+K) ratio. Total uptake of Ca, Mg, K, N and P increased and that of Na decreased in response to FYM. Contribution of Ca from Ca⁴⁵CO₃ did not differ much at different levels of FYM and it was less than 6 per cent of total Ca in plant tops in all the treatments. re]19721017     

DIFFERENTIAL RESPONSES TO MAGNESIUM AND CALCIUM BY NATIVE POPULATIONS OF AGROPYRON SPICATUM

Plants of Agropyron spicatum (Pursh) Scribn. and Smith. from populations native to serpentine and nonserpentine soils were grown at varying levels of magnesium and calcium in culture solutions. The yields of plants from the two populations were different. At high Mg levels (low Ca) the yield of the serpentine population was significantly higher than that of the nonserpentine population. At low Mg the yield of the serpentine population leveled off at a Mg: Ca ratio of 1:2, while the yield of the nonserpentine population increased up to a Mg:Ca ratio of 1:8 and showed no leveling off. Chemical analyses of tissue showed that the Ca uptake of plants from the serpentine population was significantly higher than that of the nonserpentine population. In addition, the serpentine population maintained a lower Mg concentration in the shoots than the nonserpentine population at comparable Mg substrate levels. The two populations showed differences in Ca and Mg uptake efficiency and Mg/Ca, Ca + Mg/K + Na, and Ca + Mg + K + Na in the shoots. The ecotypic differentiation with respect to Mg and Ca between native populations of serpentine and nonserpentine A. spicatum does not appear to be due to any single mechanism but, rather, a combination of several possible mechanisms, i.e., differences in root morphology, uptake mechanisms, translocation of nutrients, and interactions between cations.     

Competitive inhibition and selectivity enhancement by Ca in the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, Hf) by carrot (Daucus carota cv. U.S. harumakigosun)

We investigated the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, and Hf) and the effect of Ca on their uptake in carrots (Daucus carota cv. U.S. harumakigosun) by the radioactive multitracer technique. The experimental results suggested that Na, Mg, K, and Rb competed for the functional groups outside the cells in roots with Ca but not for the transporter-binding sites on the plasma membrrane of the root cortex cells. In contrast, Y, Ce, Pm, and Gd competed with Ca for the transporters on the plasma membrane. The selectivity, which was defined as the value obtained by dividing the concentration ratio of an elemental pair, K/Na, Rb/Na, Be/Sr, and Mg/Sr, in the presence of 0.2 and 2 ppm Ca by that of the corresponding elemental pair in the absence of Ca in the solution was estimated. The selectivity of K and Rb in roots was increased in the presence of Ca. The selectivity of Be in roots was not affected, whereas the selectivity of Mg was increased by Ca. These observations suggest that the presence of Ca in the uptake solution enhances the selectivity in the uptake of metabolically important elements against unwanted elements.     

Influence of soil oxygen and soil water on the accumulation of nutrients in avocado seedlings (Persea Americana mill.)

Summary This experiment was conducted in a greenhouse to study the influence of 2 soil-oxygen levels and 4 irrigation levels on the plant response, root decay, concentrations of 12 nutrients, as well as on total amounts of nutrients per avocado seedling (Persea americana Mill.).Reduced soil-oxygen supply to the roots significantly reduced the amount of dry weight per seedling, increased percentage of root decay, and reduced the concentrations of N, P, K, Ca, Mg, and B in the tops, while Na and Fe were increased. Concentrations of K, Mg, Na, and Cl in the roots were decreased, while N and Ca were increased with decreased soil oxygen supply to the roots. Total amounts of N, P, Ca, Mg, Na, and Cl per seedling were decreased with the low soil-oxygen supply to the roots.Only slight differences in dry weight of the tops of seedlings were found. The highest degree of root decay was caused by the irrigation treatment where a water table was present. In the tops, concentrations of N, P, K, Mg, Na, Zn, Cu, Mn, B, and Fe were significantly influenced by differential irrigation treatments; in the roots, concentrations of P, K, Ca, Mg, Na, and Cl were also significantly influenced; and total amounts of N, P, Mg, and Cl the whole seedling were likewise significantly influenced.Significant interactions were noted between the soil-oxygen and irrigation treatments on the dry weight of tops, roots, and total amounts of dry weight produced per seedling. The lowest amount of dry weight of roots and the highest degree of root decay were found in the avocado seedlings grown under low soil-oxygen supply and the irrigation treatment where a water table was present. Several significant interactions between soil oxygen and irrigation on the concentrations of N, P, K, Ca, Zn, and Mn are discussed.University of California, Citrus Research Center and Agricultural Experiment Station, Riverside, California. The research reported in this paper was supported in part by NSF Grant GB-5753x.     

Effect of divalent cations on ion fluxes and leaf photochemistry in salinized barley leaves

Photosynthetic characteristics, leaf ionic content, and net fluxes of Na(+), K(+), and Cl(-) were studied in barley (Hordeum vulgare L) plants grown hydroponically at various Na/Ca ratios. Five weeks of moderate (50 mM) or high (100 mM) NaCl stress caused a significant decline in chlorophyll content, chlorophyll fluorescence characteristics, and stomatal conductance (g(s)) in plant leaves grown at low calcium level. Supplemental Ca(2+) enabled normal photochemical efficiency of PSII (F(v)/F(m) around 0.83), restored chlorophyll content to 80-90% of control, but had a much smaller (50% of control) effect on g(s). In experiments on excised leaves, not only Ca(2+), but also other divalent cations (in particular, Ba(2+) and Mg(2+)), significantly ameliorated the otherwise toxic effect of NaCl on leaf photochemistry, thus attributing potential targets for such amelioration to leaf tissues. To study the underlying ionic mechanisms of this process, the MIFE technique was used to measure the kinetics of net Na(+), K(+), and Cl(-) fluxes from salinized barley leaf mesophyll in response to physiological concentrations of Ca(2+), Ba(2+), Mg(2+), and Zn(2+). Addition of 20 mM Na(+) as NaCl or Na(2)SO(4) to the bath caused significant uptake of Na(+) and efflux of K(+). These effects were reversed by adding 1 mM divalent cations to the bath solution, with the relative efficiency Ba(2+)>Zn(2+)=Ca(2+)>Mg(2+). Effect of divalent cations on Na(+) efflux was transient, while their application caused a prolonged shift towards K(+) uptake. This suggests that, in addition to their known ability to block non-selective cation channels (NSCC) responsible for Na(+) entry, divalent cations also control the activity or gating properties of K(+) transporters at the mesophyll cell plasma membrane, thereby assisting in maintaining the high K/Na ratio required for optimal leaf photosynthesis.     

Studies on potassium release in an inceptisol soil (Holambi Series) at the minimum level of exchangeable potassium

Summary Ammonium acetate extractable potassium in the soil reached a minimum value of 6.8 mg K/100g soil after 14 crops of wheat and pearl millet in the field without applying any potassium fertilizer. At this level of ammonium acetate extractable K both wheat and pearl millet utilized about, 90 per cent of the total K from non-exchangeable sources. Wheat and pearl millet were grown in this soil in the greenhouse at different levels of K. At K₀ level wheat utilized 86 per cent of the total K uptake from the non-exchangeable source and pearl millet, 95 per cent. At K₁ level, wheat utilized only 19 per cent but at higher levels of K, there was build up in the K status of soils. In the case of pearl millet at K₁, K₂ and K₃ levels 59, 13 and 22 per cent of total uptake were contributed by non-exchangeable forms. The total K uptake by pearl millet was more than double that by wheat. Plant analysis showed that 83 per cent of the total K in wheat was contained in the shoot portion and the rest in the roots. The corresponding figures for pearl millet were 94 and 6 per cent.     

Nutrient uptake and management under saline conditions in the xerohalophyte: Tecticornia indica (Willd.) subsp. indica

In the present investigation, we studied uptake and management of the major cations in the xerohalophyte, Tecticornia indica (Willd.) subsp. indica as subjected to salinity. Plants were grown under greenhouse conditions at various salinity levels (0, 100, 200 and 400 mM NaCl) over 110 days. At harvest, they were separated into shoots and roots then analyzed for water contents, dry weights (DW), and Na+, K+, Ca2+, and Mg2+ contents. Plants showed a growth optimum at 200 mM NaCl and much better tissue hydration under saline than non-saline conditions. At this salt concentration (200 mM NaCl), shoot Na+ content reached its highest value (7.9 mmol · g-?1 DW). In spite of such stressful conditions, salt-treated plants maintained adequate K+, Ca2+, and Mg2+ status even under severe saline conditions. This was mainly due to their aptitude to selectively acquire these essential cations and efficiently use them for biomass production.     

Lithium transport pathways in human red blood cells

In human red cells, Li is extruded against its own concentration gradient if the external medium contains Na as a dominant cation. This uphill net Li extrusion occurs in the presence of external Na but not K, Rb, Cs, choline, Mg, or Ca, is ouabain-insensitive, inhibited by phloretin, and does not require the presence of cellular ATP. Li influx into human red cells has a ouabain-sensitive and a ouabain-insensitive but phloretin-sensitive component. Ouabain-sensitive Li influx is competitively inhibited by external K and Na and probably involves the site on which the Na-K pump normally transports K into red cells. Ouabain does not inhibit Li efflux from red cells containing Li concentrations below 10 mM in the presence of high internal Na or K, whereas a ouabain-sensitive Li efflux can be measured in cells loaded to contain 140 mM Li in the presence of little or no internal Na or K. Ouabain-insensitive Li efflux is stimulated by external Na and not by K, Rb, Cs, choline, Mg, or Ca ions. Na-dependent Li efflux does not require the presence of cellular ATP and is inhibited by phloretin, furosemide, quinine, and quinidine. Experiments carried out in cells loaded in the presence of nystatin to contain either only K or only Na show that the ouabain-insensitive, phloretin-inhibited Li movements into or out of human red cells are stimulated by Na on the trans side and inhibited by Na on the cis side of the red cell membrane. The characteristics of the Na-dependent unidirectional Li fluxes and uphill Li extrusion are similar, suggesting that they are mediated by the same Na-Li countertransport system.     

Potassium Fluxes in Desheathed Frog Sciatic Nerve

Desheathed frog (R. pipiens) sciatic nerves were soaked in Na-deficient solutions, and measurements were made of their Na and K contents and of the movements of K⁴². When a nerve is in Ringer's solution, the Na fluxes are equal to the K fluxes, and about 75 per cent of the K influx is due to active transport. The Na content and the Na efflux are linearly related to the Na concentration of the bathing solution, while the K content and the K fluxes are not so related. When a nerve is in a solution in which 75 per cent of the NaCl has been replaced by choline chloride or sucrose, the active K influx exceeds the active Na efflux, and the K content is maintained. When a nerve is soaked in a solution that contains Li, the K⁴² uptake is inhibited, and the nerve loses K and gains Li. When a Li-loaded nerve recovers in a Li-free solution, K is taken up in exchange for Li. This uptake of K requires Na in the external solution. It is concluded that the active transports of K and of Na may be due to different processes, that an accumulation of K occurs only in exchange for an intracellular cation, which need not be Na, and that Na plays a specific, but unknown, role in K transport.     

Effect of the arbuscular mycorrhizal symbiosis upon uptake of cesium and other cations by plants

Pot experiments were set up to determine the species-specific uptake of cesium (Cs) by mycorrhizal (AM) and non-mycorrhizal (non-AM) plants. Using stable Cs and K application, side-effects of mineral fertilization (K) on AM development and uptake of Cs and the other cations Na, Ca and Mg were investigated. AM colonization by the fungus Glomus mosseae led to a significant decrease in shoot Cs content of Agrostis tenuis from the first (4 weeks) to the third harvest (8 weeks). With regard to the root system, statistically significant differences were observed from the first (4 weeks) to the second harvest (6 weeks). Supply of additional K produced a significant decrease in Cs uptake by both AM and non-AM plants over a 10-week period. In the case of AM plant shoots, K fertilization did not very effectively reduce Cs uptake by A. tenuis. Cs contents of fertilized AM roots were similar to non-AM controls. Potassium application resulted in an increase in K content and a slight reduction in Na and Mg contents of shoots and roots. Without K fertilization, the Na content of non-AM controls was significantly enhanced over AM shoots. Shoot and root Ca contents were generally higher without than with K addition. Negative side-effects of K fertilization as a countermeasure to Cs uptake were not observed in relation to AM development. The intensity of colonization by G. mosseae was not significantly depressed by K treatment. AM development in plants appeared to decrease Cs uptake, at least at moderate nutrient levels. It is possible that Cs is sequestered by AM extraradical fungal hyphae and consequently not transferred to the plant to the extent found in non-AM roots. Accepted: 6 November 2000     

Cation Transport in Escherichia coli : IV. Kinetics of net K uptake

The resuspension of K-poor, Na-rich stationary phase E. coli in fresh medium at pH 7.0 results in a rapid uptake of K and extrusion of Na by the cells. In all experiments net K uptake exceeded net Na extrusion. An investigation of the uptake of glucose, PO₄, and Mg and the secretion of H by these cells indicates that the excess K uptake is not balanced by the simultaneous uptake of anions but must be accompanied by the extrusion of cations from the cell. The kinetics of net K uptake are consistent with the existence of two parallel influx processes. The first is rapid, of brief duration, and accounts for approximately 60 per cent of the total net K uptake. This process is a function of the extracellular K concentration, is inhibited in acid media, and appears to be a 1 for 1 exchange of extracellular K for intracellular H. The second influx process has a half-time of approximately 12 minutes, and is not affected by acid media. This process is a function of the intracellular Na concentration, is dependent upon the presence of K in the medium, and may be ascribed to a 1 for 1 exchange of extracellular K for intracellular Na.     

Selectivity of alkali cation influx across the plasma membrane of oat roots: cation specificity of the plasma membrane ATPase

Influx of alkali cations (Li(+), Na(+), K(+), Rb(+), Cs(+)) across plasma membranes of cells of excised roots of Avena sativa cv. Goodfield was selective, but different, in the absence and in the presence of 1 mm CaSO(4). Ca(2+) reduced the influx rates of all of the alkali cations-especially Na(+) and Li(+). Transport selectivity changed as the external concentrations of the alkali cations increased.Plasma membrane ATPase, purified from Avena sativa roots, was differentially stimulated by alkali cations. This specificity, however, was not altered by Ca(2+) or the external cation concentrations. A close correspondence existed between the relative influx rates of K(+), Rb(+), and Cs(+) and the relative stimulation of the ATPase by these cations. A similar correspondence did not occur for Na(+) and Li(+).Selective cation transport in oat roots could result, in part, from the specificity of the plasma membrane ATPase, but other factors such as specific carriers or porters or differential diffusion rates must also be involved.     

Aluminium effects on growth, nutrient net uptake and transport in 3 rice (Oryza sativa) cultivars with different sensitivity to aluminium

Varietal differences in net nutrient uptake rate and transport efficiency in the presence of aluminium have seldom been investigated in rice. Therefore, effects of Al on growth, uptake and transport of macronutrients (K, P, Ca, and Mg) and micronutrients (Fe, Zn, Cu, and Mn) were evaluated in 3 rice cultivars (BG35, DA14 and IR45) with different Al sensitivity. The plants were grown in nutrient solution at pH 4.1. An initial growth was completed in the time interval 1 to 5 days immediately before the addition of Al. The final growth period with Al (0, 140, 280 or 560 μ M ) was completed on day 26. With Al, a comparatively high P accumulation occurred in shoots and roots of the Al tolerant cultivar BG35. In contrast, the Al sensitive cultivar IR45 maintained a relatively high Ca accumulation during the Al treatment. A reduced total net uptake rate of P and Ca by IR45 in the time period 5 to 26 days was due to both a reduced root fresh weight and a reduced net uptake rate per g fresh weight of root. Moreover, net Ca transport to the shoots higher than net uptake rate in DA14 and IR45 at > 140 μ M Al during the test period suggests restricted Ca uptake by the roots in combination with a continuous net loss of Ca from the roots to the shoots as time proceeds. In the case of Mg and Mn, there was a general reduction of net uptake rates, irrespective of Al sensitivity of cultivars. With Al treatment, comparatively high accumulation of Fe, Zn and Cu occurred in the roots of IR45, concomitant with a high net Zn and Cu uptake rate. It is concluded that differences in Al sensitivity among rice cultivars BG35, DA14 and IR45 are not primarily linked to the depressed internal Mg or Mn status of the plants but rather to changes in the uptake and distribution of Ca and P.     

Membrane Adenosine Triphosphatase of Escherichia coli: Activation by Calcium Ion and Inhibition by Monovalent Cations

Membrane ghost preparations of Escherichia coli K-12 obtained by osmotic lysis of lysozyme-induced spheroplasts were found to possess both Mg(++)- and Ca(++)-activated adenosine 5'-triphosphatase (ATPase, EC 3.6.1.3) activities. Maximal activities of 1.0 to 1.5 mumoles of orthophosphate released per min per mg of protein were obtained at pH 9.0 with a molar Mg(++) to adenosine 5'triphosphate (ATP) ratio of 2:5 and at pH 9.9 with a molar Ca(++) to ATP ratio of 1:5. These ATPase activities were not altered by ouabain, fluoride, N-ethylmaleimide, 2,4-dinitrophenol, cyanide, or dithionite, but were inhibited by low concentrations of azide, p-chloromercuribenzoate, and pentachlorophenol. Mg(++) ATPase was more susceptible to inhibition by azide than was Ca(++) ATPase. Fifty per cent inactivation of both activities was observed when membrane ghost preparations were preincubated at 66 C for 10 min. The Mg(++) and Ca(++) ATPase activities of these preparations were not additive, but did respond independently to inhibition by monovalent cations. Ca(++) ATPase was found to be very sensitive to inhibition by K(+), Na(+), Li(+), Rb(+), and Cs(+); Mg(++) ATPase was relatively insensitive to these ions. One possible interpretation of the results presented in this paper is that the membrane of E. coli possesses an ATPase which is activated by either Mg(++) or Ca(++) and that activation by Ca(++) increases the susceptibility of this enzyme to inhibition by monovalent cations. Increased susceptibility of E. coli membrane ATPase to inhibition by monovalent cations such as Na(+) and K(+) as a consequence of Ca(++) activation could represent a regulatory mechanism.     

Separating multiple, short-term, deleterious effects of saline solutions on the growth of cowpea seedlings

? Reductions in plant growth as a result of salinity are of global importance in natural and agricultural landscapes. ? Short-term (48-h) solution culture experiments studied 404 treatments with seedlings of cowpea (Vigna unguiculata cv Caloona) to examine the multiple deleterious effects of calcium (Ca), magnesium (Mg), sodium (Na) or potassium (K). ? Growth was poorly related to the ion activities in the bulk solution, but was closely related to the calculated activities at the outer surface of the plasma membrane, {I(z)}?°. The addition of Mg, Na or K may induce Ca deficiency in roots by driving {Ca2+}?° to < 1.6 mM. Shoots were more sensitive than roots to osmolarity. Specific ion toxicities reduced root elongation in the order Ca2+ > Mg2+ > Na+ > K+. The addition of K and, to a lesser extent, Ca alleviated the toxic effects of Na. Thus, Ca is essential but may also be intoxicating or ameliorative. ? The data demonstrate that the short-term growth of cowpea seedlings in saline solutions may be limited by Ca deficiency, osmotic effects and specific ion toxicities, and K and Ca alleviate Na toxicity. A multiple regression model related root growth to osmolarity and {I(z)}?° (R2=0.924), allowing the quantification of their effects.