Monitoring uptake and contents of Mg,Ca and K in Norway spruce as influenced by pH and Al,using microprobe analysis and stable isotope labelling

In a model system using intact spruce trees (Picea abies [L.] Karst.) we followed the path of magnesium, calcium and potassium during uptake into the root and during long-range transport into the shoot, by multiple stable isotope labelling. The roots of two- and three-year-old spruce trees originating from soil culture were removed from the soil and, in part or in toto, exposed to labelling solutions containing the stable isotopes ²⁵Mg or ²⁶Mg, ⁴¹K and ⁴²Ca or ⁴⁴Ca. Optical-emission-spectroscopy (ICP-OES) of plant fractions and labelling solutions was combined with the quantitative analysis of stable isotope ratios in sections of shock frozen, cryosubstituted material using the laser-microprobe-mass-analyser (LAMMA). This combination allowed us to distinguish, both in bulk samples and on the cellular level between (i) the fraction of elements originally present in the plant before the start of the labelling, (ii) the material taken up from the labelling solution into the plant and (iii) any material released by the plant into the labelling solution.In single-root labelling experiments, roots of three-year-old spruce trees, grown in nursery soil, were exposed to various pH conditions. The exchange of Mg and Ca with the labelling solution was nearly 100% in the cell walls of the mycorrhized finest roots. This exchange was only slightly affected by a step down to pH 3.5. The absolute Mg and Ca content in the cell walls was moderately reduced by incubation at pH 3.5 and strongly reduced in the presence of Al at this pH. After a pH 3.5 and 2 mM Al treatment we found Al in the xylem cell walls and the cortex cell lumina at elevated concentrations. To analyse the combined effect of high Al and high proton concentrations on the long-range transport, we used a split-root system. The root mass of an intact two-year-old spruce tree, grown in mineral soil, was divided into even parts and both halves incubated in solutions with two sets of different stable isotopes of Mg and Ca (side A: no Al, ²⁵Mg and ⁴²Ca; side B: +Al, ²⁶Mg and ⁴⁴Ca) and ⁴¹K on both sides. We observed a large uptake of Mg, Ca and K into the plant and a pronounced release. The net uptake of all three elements was lower from the Al-doted solution. In cross-sections of the apical shoot we found after seven-day labelling period about 60–70% of the Mg and Ca and 30% of the K content in the xylem cell walls originating from both labelling solutions. The clear majority of the Mg and Ca label originated from the Al-doted side.     

Top and root growth and nutrient absorption of Prunus avium L. at two soil pH and P levels

One-year-old Prunus avium L. were grown under greenhouse conditions in a Countesswells soil in all combinations of 2 pH and 2 P levels. The soil, obtained from a long-term liming and fertilizer experiment, provided pH values throughout the experiment of 3.75–3.99 (pH 1) and 4.81–5.41 (pH 2). The P treatments had 0.43% acetic acid extractable P of 31–44 g g^-1 (P1) and 145–173 g g^-1 (P2). The trees were harvested 92 (H1), 134 (H2), and 168 (H3) days after initiation of growth.Top (leaf+new stem) dry weight was significantly increased for pH 2 and P2 at H2 and H3. P2 also increased leaf weight (H1), the weight of the original stem-root (H2 and H3), and root length but decreased root diameter at both soil pHs (H2 and H3). Total tree uptake of N, P, K, Ca, and Mg was also increased by pH-P combinations which had significantly greater dry matter production and root length. Total Mn uptake decreased at pH2. Root nutrient inflows (uM m^-1 day^-1) were increased for Ca at pH2 and for P at P2. Mn inflow decreased at pH2 and at pH1 P2 although the increased root length associated with the latter treatmen resulted in increased total tree Mn uptake. In general, high nutrient inflows occurred in all trees at H1 and in severely stunted trees at pH1 P1; both had larger than average root diameters.     

Charybdotoxin blocks with high affinity the Ca-activated K+ channel of Hb A and Hb S red cells: Individual differences in the number of channels

Summary We have investigated the effect of a purified preparation of Charybdotoxin (CTX) on the Ca-activated K⁺ (Ca–K) channel of human red cells (RBC). Cytosolic Ca²⁺ was increased either by ATP depletion or by the Ca ionophore A23187 and incubation in Na⁺ media containing CaCl₂. The Ca–K efflux activated by metabolic depletion was partially (77%) inhibited from 15.8±2.4 mmol/liter cell · hr, to 3.7±1.0 mmol/liter cell · hr by 6nm CTX (n=3). The kinetic of Ca–K efflux was studied by increasing cell ionized Ca²⁺ using A23187 (60 mol/liter cell), and buffering with EGTA or citrate; initial rates of net K⁺ efflux (90 mmol/liter cell K⁺) into Na⁺ medium containing glucose, ouabain, bumetanide at pH 7.4 were measured. Ca–K efflux increased in a sigmoidal fashion (n of Hill 1.8) when Ca²⁺ was raised, with aK _m of 0.37 m and saturating between 2 and 10 m Ca²⁺. Ca–K efflux was partially blocked (71±7.8%, mean ±sd,n=17) by CTX with high affinity (IC₅₀0.8nm), a finding suggesting that is a high affinity ligand of Ca–K channels. CTX also blocked 72% of the Ca-activated K⁺ efflux into 75mm K⁺ medium, which counteracted membrane hyperpolarization, cell acidification and cell shrinkage produced by opening of the K⁺ channel in Na⁺ media. CTX did not block Valinomycin-activated K⁺ efflux into Na⁺ or K⁺ medium and therefore it does not inhibit K⁺ movement coupled to anion conductive permeability.TheV _max, but not theK _m–Ca of Ca–K efflux showed large individual differences varying between 4.8 and 15.8 mmol/liter cell · min (FU). In red cells with Hb A,V _max was 9.36±3.0 FU (mean ±sd,n=17). TheV _max of the CTX-sensitive, Ca–K efflux was 6.27±2.5 FU (range 3.4 to 16.4 FU) in Hb A red cells and it was not significantly different in Hb S (6.75±3.2 FU,n=8). Since there is larger fraction of reticulocytes in Hb S red cells, this finding indicates that cell age might not be an important determinant of theV _max of Ca–K⁺ efflux.Estimation of the number of CTX-sensitive Ca-activated K⁺ channels per cell indicate that there are 1 to 3 channels/per cell either in Hb A or Hb S red cells. The CTX-insensitive K⁺ efflux (2.7±0.9 FU) may reflect the activity of a different channel, nonspecific changes in permeability or coupling to an anion conductive pathway.     

Aluminium accumulation in root cell walls coincides with inhibition of root growth but not with inhibition of magnesium uptake in Norway spruce

High levels of aluminium in the soil solution of forest soils cause stress to forest trees. Within the soil profile, pH and aluminium concentration in the soil solution vary considerably with soil depth. pH strongly influences the speciation of A1 in solution, and is a factor when considering toxicity of A1 to roots. Norway spruce ( Picea abies [L.] Karst.) seedlings were grown for 7 weeks in nutrient solutions at pH 3.2, 4.0 or 5.0 containing 0, 100 or 400 µ M A1. At the end of this period, seedling growth, the cation exchange capacity of the roots and the amount of exchangeable Ca and Mg in roots were determined. A1 concentrations in whole roots, root segments, and in needles were measured. Using X‐ray microanalysis, the concentrations of Al, Ca, Mg and P were determined in cortical cell walls. We wanted to test the hypotheses that (1) the amount of Al bound to cation exchange sites can be used as a marker for Al toxicity and (2) the Mg concentration of needles is controlled by the amount of Mg bound to cation exchange sites. Low pH reduced the inhibition of Al on root growth and shoot length. Both low pH and Al lowered the concentration of Ca and Mg in needles. Al concentrations in the roots decreased as the pH decreased. In the roots, Al displaced Mg and Ca from binding sites at the root cortical cell walls. A comparison of the effects of Al at the different pH values on root growth and Mg concentration in the needles, suggests that, at pH 5.0, an Al fraction in the apoplast inhibits root growth, but does not affect Mg uptake. This fraction of Al is not available for transport to the shoots. In contrast, Mg uptake is strongly affected by Al at pH 3.2, although only very low levels of Al were detected in the roots. Thus, Al accumulation in the apoplast is a positive marker for Al effects on root growth, but not Mg uptake. The Mg concentration of needles is not controlled by the amount of Mg bound to cation exchange sites.     

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

Effect of artificial soil acidification and liming on growth and nutrient status of mycorrhizal roots of Norway spruce (Picea abies [L.] Karst.)

Effects of soil acidification and liming on biomass responses and free Al, Ca, K, Mg, Mn and P contents of mycorrhizal roots of mature Norway spruce (Picea abies [L.] Karst.) were studied at Höglwald Forest in Southern Germany.At the untreated site, mycorrhizal root biomass was lower in the acid humus (pH = 3.3) than in the less acid upper (0–5 cm) mineral soil (pH 4.1). Mycorrhizal roots from the humus contained 10% of the level free Al in mycorrhizal roots from the upper mineral soil. During seven years of soil acidification the quantity of mycorrhizal roots remained unaffected in the humus and the upper mineral soil, perhaps due to the high buffering capacity of the humus which prevented a significant alteration of the nutrient status of the roots. However, two years after soil acidification had been terminated, the percentage of mycorrhizal roots in the humus decreased, possibly because the free root concentrations of K had decreased.On the other hand, six years after liming, there was a two-fold increase of the annual mean quantity of mycorrhizal roots in the humus. Compensatory liming (acid irrigation after liming) had a similar effect on mycorrhizal root production in the humus. However, two years after acid irrigation had been terminated a decrease of mycorrhizal roots in the upper mineral soil (0–5 cm) was observed. Since the total amount of mycorrhizal roots in the humus and upper mineral soil remained constant, compensatory liming produced a shift in fine roots to the humus layer.The higher mass of living mycorrhizal roots in the upper mineral soil (0–5 cm) as compared to the humus of the untreated plot as well as the increased mass of mycorrhizal roots in the humus after liming or compensatory liming are both attributed to an increase in pH to 4.5 rather than alleviation of Al toxicity.     

Metal-humic complexes and plant micronutrient uptake: a study based on different plant species cultivated in diverse soil types

There are several studies in the literature dealing with the effect of metal-humic complexes on plant metal uptake, but none of them correlate the physicochemical properties of the complexes with agronomic results. Our study covers both aspects under various experimental conditions. A humic extract (SHE) obtained from a sapric peat was selected for preparing the metal–humic complexes used in plant experiments. Fe–, Zn– and Cu–humic complexes with a reaction stoichiometry of 2:0.25 (humic:metal, w/w) were chosen after studying their stability and solubility with respect to pH (6–9) and the humic:metal reaction stoichiometry. Wheat and alfalfa plants were greenhouse cultured in pots containing one of three model soils: an acid, sandy soil and two alkaline, calcareous soils. Treatments were: control (no additions), SHE (53 mg kg^–1 of SHE), and metal (Cu, Zn and Fe)–SHE complexes (2.5 and 5 mg kg^–1 of metal rate and a SHE concentration to make 53 mg kg ^–1). Cu- and Zn–humic complexes significantly (p0.05) increased the plant uptake and the DTPA-extractable soil fraction of complexed micronutrients in most plant–soil systems. However, these effects were associated with significant increases (p0.05) of shoot and root dry weight only in alfalfa plants. In wheat, significant increases of root and shoot dry matter were only observed in the Cu–humic treated plants growing in the acid soil, where Cu deficiency was more intense. The Fe–humic complex did not increase Fe plant assimilation in any plant–soil system, but SHE increased Fe-uptake and/or DTPA-extractable soil Fe in the wheat–calcareous soil systems. These results, taken together with those obtained from the study of the pH- and SHE:metal ratio-dependent SHE complex solubility and stability, highlight the importance of the humic:Fe complex stoichiometry on iron bioavailability as a result of its influence on complex solubility.     

Oxidative fermentation of calcium-magnesium lactate to calcium-magnesium acetate deicing salt

Summary The oxidation of Ca–Mg lactate to Ca–Mg acetate (CMA) deicing salt was studied in pure cultures ofAcetobacter pasteurianus, Gluconobacter cerinus orG. oxydans. Gluconobacter sp., which maintained a practically self-controlled pH reaction and did not overoxidize acetate, appear to be potentially important for CMA production.     

The effect of Mg on Ca,K and P content of date palm seedlings under mycorrhizal and non-mycorrhizal conditions

The effects of the presence or absence of Mg in the nutrient solution and of vesicular-arbuscular mycorrhizal fungi (VAMF) on the content and partitioning of Ca, K and P between root and shoot of date palm (Phoenix dactylifera) seedlings were examined under greenhouse conditions using soil as basal medium. Mg content of the soil was 14.95 µmol/g dry soil. The infection percentages after inoculation of VAMF were 66.0% and 55.5%, respectively, on application of –Mg and +Mg nutrient solution. Ca content of both roots and shoots did not change by these treatments; but a highly significant decrease in shoots was recorded on –Mg and +VAMF treatment. K content of root was significantly elevated by –Mg and +VAMF treatment but no changes were observed in shoots. P content of both roots and shoots increased significantly with +VAMF regardless of the presence or absence of Mg.     

Sensitivity to H- and Al ions limiting growth and distribution of the woodland grass Bromus benekenii

One pH experiment and two aluminium experiments were conducted in order to investigate the effects of H- and Al ions on growth of Bromus benekenii. Continuously flowing solution cultures were used with ion concentrations simulating natural soil solutions. In all experiments, treatment effects were more pronounced on root than on shoot growth. In the pH experiment, root growth decreased with decreasing pH within the pH range 4.5 to 3.5. The critical pH for root growth of Bromus benekenii was between 3.8 and 4.0. In the Al experiments, root growth started to decrease at 20 M of quickly reacting Al and almost ceased at 70 M Al. This characterizes Bromus benekenii as an Al sensitive species. In the pH experiment, shoot concentrations of Ca, Mg, K and P decreased with decreasing pH, but root concentrations were not affected. In the Al experiments, the Al concentrations of both shoots and roots increased with Al in the nutrient solution. At treatments of 70 M Al or higher, Ca, Mg, K and P concentrations in the shoots were reduced. The critical concentrations of H- and Al ions in the experiments were similar to the highest concentrations found at field sites of Bromus benekenii, analysed in soil solutions obtained by centrifugation technique. Both Al and H toxicity were considered to be of importance as limiting factors for the distribution of Bromus benekenii in south Sweden. Probably, Al toxicity starts to limit growth when also pH itself influences growth negatively. The importance of simulating natural soil solutions in experiments is emphazised, in order to obtain information on the importance of chemical soil factors to the distribution of plants.     

Ion exchange properties of plant root cell walls

Acid-base properties and the swelling capacity of wheat, lupin and pea root cell walls were investigated. Roots of seedlings and green plants of different age were analysed by the potentiometric method. The ion exchange capacity (S _i) and the swelling coefficient (K ^cw) of root cell walls were estimated at various pH values (from 2 to 12) and at different ionic strength (between 0.3 and 1000 mM). To analyse the polysigmoid titration curves pH_i = f (S _i), the Gregor's equation was employed. It was shown that the Gregor's model fits well the experimental data. The total number of the cation exchange (S _t ^cat) and the anion exchange (S _t ^an) groups were determined in the root cell walls. The number of the functional group of each type (S ^j) was estimated, and the corresponding values of pK _a ^j were calculated. It was shown that for all types of cation exchangeable groups arranged in the cell wall structure the acid properties are enhanced by the increasing concentration of electrolyte. For each ionogenic group the coefficients of Helfferich's equation [pK _a ^j = f (C ^K+)] were determined. It was found that the swelling of root cell walls changes with pH, C ^K+ and strongly depends on plant species. Within the experimental pH and C ^K+ range the swelling coefficient changes as follows: lupin > pea > wheat. The obtained results show that for the plant species under investigation the differences in the swelling coefficients originate from (a) the differences in the cross-linking degrees of polymeric chains arranged in the cell wall structure, (b) the differences in the number of carboxyl groups and (c) the differences in the total number of functional groups. Based on the estimated swelling coefficients in water it could be inferred that for wheat the cross-linking degree of the polymeric chains in the root cell walls is higher than those for lupin or pea. It has been emphasized that the calculated parameters (S ^j, pK _a ^j, K ^cw), the equation {pK _a ^j = f (C^K+)} and the dependencies {K ^cw = f (C^K+, pH)} allow to estimate quantitatively the changes in the ion exchange capacity of the root cell walls in response to the changes in an ionic composition of an outer solution. The results of these estimations allow to suggest that (a) the root apoplast is a compartment where the accumulation of cations takes place during the first stage of cation uptake from an outer medium, and (b) the accumulation degree is defined by pH and ionic composition of an outer solution. On the basis of the literature review and the results of the present experimental study it was proposed that the changes in the cell wall swelling in response to variances of environmental or experimental conditions could lead to a change of the water flow through a root apoplast. It has been supported that there is direct relationship between the swelling of root cell walls and the water flow within the plant root apoplast.     

Interacting effects of pH,aluminium and base cations on growth and mineral composition of the woodland grasses Bromus benekenii and Hordelymus europaeus

The influence of base cation concentrations on pH and aluminium sensitivity of the woodland grasses Bromus benekenii and Hordelymus europaeus was studied in flowing solution culture experiments. Plants were exposed to low pH (3.9, experiment 1) and Al concentrations of 19 and 37 M (experiment 2) at two base cation (Ca+Mg+K) levels, all within the ranges measured in natural forest soil solutions. Elevated base cation concentrations ameliorated both H and Al toxicity, as indicated by increased root and shoot growth. In the third experiment, interactions between pH (4.3 and 4.0) and Al (0 and 19 M) were investigated. It was shown that the combined toxicity effects of H and Al were not greater than the separate H or Al effects. Tissue concentrations of base cations and Al increased with increasing concentrations in the solution, but were also influenced by the base cation : Al ratio. Relating the experimental evidence with the composition of forest soil solutions suggests an important role of soil pH and Al in controlling the distribution of the two species. Growth conditions also differ at various soil depths. Concentrations of free cationic Al were higher and base cation concentrations lower at 5–10 cm than at 0–5 cm soil depth. Increasing base cation concentrations may protect roots from both H and Al injury during periods of drought when concentrations of most elements increase in the soil solution, whereas molar ratios between base cations, H and Al remain unchanged.     

Preliminary compositional nutrient diagnosis norms for cowpea (Vigna unguiculata (L.) Walp.) grown on desert calcareous soil

This study calculated the compositional nutrient diagnosis (CND) norms of cowpea (Vigna unguiculata (L.) Walp.), as well as identified significant nutrient interactions of this crop growing in an irrigated calcareous desert soil. Three genotypes were distributed in rows in a 2-ha field. The soil showed high heterogeneity in its chemical properties. For statistical analysis, 86 foliar composite samples from healthy plants were used. Preliminary CND norms were developed using a cumulative variance ratio function and the ² distribution function. Means and standard deviations of row-centered log ratios V_X of five nutrients (N, P, K, Ca, and Mg) and a filling value R, which included all nutrients not chemically analyzed. Preliminary CND norms are: V_N^*=0.174±0.095, V_P^*=–2.172±0.234, V_K^*=–0.007±0.267, V_Ca^*=–0.022±0.146, V_Mg^*=–1.710±0.132, and V_R5^*=3.728±0.084. These CND norms are associated with dry bean yields higher than 1.88 t ha^–1, and are associated with the following foliar concentrations: 26.2 g N kg^–1, 2.5 g P kg^–1, 22.9 g K kg^–1, 21.6 g Ca kg^–1, and 4 g Mg kg^–1. Cowpea plants growing in desert calcareous soils took up lower amounts of N, P, and K than those considered as optimum in a previous report. Six interactions were strongly indicated for cowpea through principal component analyses: positive for Ca–Mg, and negative for N–Ca, N–Mg, Ca–P, Mg–P, and K–P. Furthermore, two interactions were identified using simple correlations, negative N–P and positive K–Ca.     

Dry matter yield,root traits,and nodule occupancy of lucerne and Caucasian clover when grown in acidic soil with high aluminium concentrations

Aims and methods

Lucerne and Caucasian clover dry matter were measured in response to recommended lime and capital P inputs for six years in an acidic soil in the New Zealand high country. The initial three years of the field experiment indicated successful establishment and persistence of both legumes. Lucerne dry matter (DM) yield was up to 4 t/ha/yr in this period and higher than Caucasian clover yields. However, a lack of persistence of lucerne was apparent from this point forward compared with Caucasian clover which produced 7.7 t DM/ha in Year 6. An experiment using tubes of soil was used to investigate whether differences in root traits, nodulation and nodule occupancy were responsible for the differences observed in field persistence over time.

Results

These showed that when rhizobia inoculant was added, the fine root length of Caucasian clover was unaffected (R² = 0.14) by aluminium (Al) content of the soil. In contrast, fine root growth of lucerne was suppressed (R² = 0.79) by the soil Al content. Nodulation of Caucasian clover was unaffected by soil pH or Al when the rhizobia inoculant was provided which suggests the viability of the commercial genotype ICC148 in this soil with a pH of 5.5 and Al ca. 7 mg/kg soil. For lucerne, the maximum nodulation score of 7.3 occurred with 2 t/ha of lime added (soil pH ca.6, Al ca. 0.3 mg/kg) plus inoculant.

Conclusions

This suggests an Al toxic threshold of <1.0 mg Al/kg soil for effective lucerne nodulation. From the lucerne nodules, eight naturalized strains of Ensifer meliloti were identified. In contrast, only one R. leguminosarum strain was detected in the Caucasian clover nodules. The competition between those rhizobia genotypes may negatively affect the efficiency of biological nitrogen fixation in lucerne. Therefore, the lack of genetic diversity of R. leguminosarum bv. trifolii in New Zealand soils might be an advantage especially if the commercial strain is acid soil tolerant.

     

Studies on the cation permeability of human red cell ghosts

Summary Net K movements in reconstituted human red cell ghosts and the resealing of ghosts to cations after osmotic hemolysis of red cells have been studied as functions of the free Ca ion concentration. The Ca-dependent specific increase in K permeability was shown to be mediated by a site close to the internal surface of the membrane with an apparent dissociation constant at pH 7.2 for Ca (K _D1) of 3–5×10^–7 m, for Sr of 7×10^–6 m. Ba and Mg did not increase the K-permeability of the membrane but inhibited the Ca-mediated permeability changes.K _D1 decreased in a nonlinear fashion when the pH was increased from 6.0 to 8.5. Two different pK values of this membrane site were found at pH 8.3 and 6.3. The Ca-activated net K efflux into a K-free medium was almost completely inhibited by an increase in intracellular Na from 4 to 70mm. Extracellular K antagonized this Na effect. Changes in the extracellular Na (0.1–140mm) or K(0.1–6mm) concentrations had little effect and did not changeK _D1. The Ca-stimulated recovery of a low cation permeability in ghost cells appeared to be mediated by a second membrane site which was accessible to divalent cations only during the process of hemolysis in media of low ionic strength. The apparent dissociation constant for Ca at this site (K _D2) varied between 6×10^–7 and 4×10^–6 m at pH 7.2. Mg, Sr, and Ba could replace Ca functionally. The selectivity sequence was Ca>Sr>Ba>Mg.K _D2 was independt on the pH value in the range between 6.0 and 8.0. Hill coefficients of 2 were observed for the interaction of Ca with both membrane sites suggesting that more than one Ca ion is bound per site. The Hill coefficients were affected neither by the ion composition nor by the pH values of the intra- and extracellular media. It is concluded that two different pathways for the permeation of cations across the membrane are controlled by membrane sites with high affinities for Ca: One specific for K, one unspecific with respect to cations. The K-specific channel has properties similar to the K channel in excitable tissues.     

Microbeam analysis of Ca exchange and uptake in the fine roots of spruce: influence of pH and aluminum

Summary A novel stable isotope labelling procedure for microbeam analysis was developed to monitor exchange and uptake of nutrients, primarily Mg, K and Ca, by root tips at the cellular level. Initially root samples were analysed from 2-year-old spruce trees, originating both from a nursery and from a polluted forest site, (1) for the cortex cell wall accessibility and nutrient binding properties, (2) for the influence of low pH and elevated aluminum concentrations on Ca binding to cortex cell walls, and (3) for long-range transport into the secondary xylem, proximal to the labelled root tip. In nursery control plants, Ca is localized mainly in the apoplast of the cortex. Exchange of Mg, K, Ca in the cell wall of the cortex and the primary xylem with label in incubation solutions is almost completed to equilibration within 30 min. In the secondary xylem we could detect Mg, K, and Ca from labelling solutions in minute amounts after 30 min, and as a major fraction after 48 h. This indicates that stable isotope labelling can be used to study both ion-exchange properties of the apoplast and long-range transport. Slight acidification of the labelling incubation media to pH 4.5 reduced Ca binding to the cortex cell walls slightly, but acidification to the extreme value of pH 2.3 reduced binding 41%. A combination of pH 4.5 and increased free aluminum reduced the binding by 83%. In a preliminary attempt to analyse the nutrient binding capability of the root-tip apoplast from pollution affected trees, we exposed fine roots of 2-year-old spruce from an acidified and polluted site showing typical low levels of Ca and Mg in the cortical cell walls to Ca-enriched media. Under these conditions the Ca content of cortex cell walls doubled upon incubation at pH 4.7, reaching 40% of the total binding capacity of our nursey control plants.     

Biotechnological potential of Chlorella vulgaris for accumulation of Cu and Ni from single and binary metal solutions

This study provides information on the mechanism(s) of Cu and Ni ion biosorption by C. vulgaris, distinguishing adsorption from intracellular accumulation under various conditions. Surface adsorption was found to contribute maximally (>70%) to total Cu/Ni ion accumulation by the test alga (total accumulation efficiencies were 60 and 53 g metal ion mg protein^–1, respectively for Cu and Ni). Maximum intracellular uptake was reported at a pH range of 6.5–7.5, whereas adsorption reached its maximum at pH 3.5 for Cu, and pH 3.5 and 6.5 in the case of Ni. 35 °C was found to be the best temperature for maximum adsorption, whereas intracellular uptake was highest at 25 °C. Though exponentially grown C. vulgaris registered maximum metal ion uptake, adsorption maxima reached the highest values in the declining phase of the culture. Heat-killed and air-dried C. vulgaris accumulated Cu and Ni at about 80% of the values for viable samples, whereas formaldehyde-treated and immobilized biomasses depicted better accumulating potential than the control cells. Na, K, Mn and Zn caused competitive inhibition, whereas for Ca a mixed-type inhibition was evident. Thus, the present study suggests that the general concept that cations inhibit metal ion accumulation by competing with them for the same binding sites on the cell surface is not absolutely valid. As these results also demonstrate that a large amount of the bound metal (>70%) is in the adsorbed fraction, it is advantageous in the sense that it could be recovered by a suitable desorbing agent, especially in case of precious metals and the biomass could be exploited for repeated use in reactors.     

Factors affecting soil acidification under legumes I. Effect of potassium supply

This study examined the effect of K (as K₂SO₄) supply on acid production under N₂-fixing plants of lupin (Lupinus angustifolius L. cv. Gungurru) and clover (Trifolium subterraneum L. cv. Dalkeith) grown in a K-deficient soil with a low pH buffer capacity for 55 days in the glasshouse at 20/12 °C (day/night). Increasing K supply up to 240 mg K kg^-1 soil markedly increased plant growth of both species but clover growth was more responsive than lupin. Growing plants for 55 days decreased soil pH by 0.65–0.85 units under lupin and 0.45–0.83 units under clover. The amounts of H⁺ produced per kg biomass (specific acid production) were the highest at the nil K supply, generally decreased with increasing K level up to 30 mg K kg^-1 under lupin and up to 120 mg K kg^-1 soil under clover and only slightly increased with further increasing K under lupin. Increasing K₂SO₄ supply proportionally increased plant uptake of K and SO ₄ ^2- but generally decreased concentrations of Ca, Mg, Na, P and Cl. Specific acid production correlated well with concentrations of excess cations and ash alkalinity, and total acid production was strongly correlated with total excess cations and total ash alkalinity in plants. These relationships were not affected by K treatment and species. Specific acid production also correlated with plant Ca concentration but not with K concentration. In addition, lupin and clover extruded similar amounts of H⁺ per kg biomass produced. It is suggested that application of K₂SO₄ does not have a significant impact on acid production by lupin and clover.     

Polyamines and Pectins (I. Ion Exchange and Selectivity)

The ion-binding and -exchange properties of putrescine, spermidine, and spermine on purified walls of carrot (Daucus carota L.) cell suspensions were investigated by producing ion-exchange isotherms and comparing them with the behavior of Na+, Mg2+, and Ca2+. The cation exchange capacity of the carrot cell walls was 0.8 equivalent kg-1 dry matter, and the ionic selectivity sequence of the walls for polyamines followed the sequence spermine4+ > spermidine3+ [almost equal to] Ca2+ > putrescine2+. The polyamines were subjected to only electroselectivity and probably did not induce any favorable supramolecular conformation of pectin like the one induced by Ca2+. Triangular ion exchanges were also performed with three diamines: ethanediamine, butanediamine, and octanediamine. The shorter the diamine, the higher the total adsorption and selectivity of the exchange. The lower selectivity of the cell wall for putrescine was partly attributed to its inability to access and displace Ca2+ from higher affinity sites within dimerized pectic sequences. The polyamine adsorption and exchange on pectic sequences could result in pectic signal modulation in pathogenesis and in differentiation.     

Nutrient flow rates in rice roots under varying drainage conditions

Summary The relative importance of massflow and diffusion in supplying nutrients to plant roots under various drainage conditions is tested. Rice (Oryza sativa L. variety Jaya) plants were grown in field lysimeters. Transpiration, nutrient content and root length were measured along with the soil solution composition at four stages of growth. The mean inflow, apparent massflow and root demand coefficients were calculated for different nutrients.The mean inflow values of N and P were highest in continuous drainage followed by no drainage and flooding followed by 2– and 4-day drainage conditions. Inflow values of K, Ca, Mg and Na, however, were lowest in no drainage. The apparent massflow of K was lower and that of Na, Ca as well as well as Mg was higher than the corresponding inflow values. Mean solution concentration of K at the root surface decreased, but that of Ca, Mg and Na increased slightly. Root demand coefficients of K, Ca, Mg and Na were highest in continuous drainage. Under different water management practices, the values of inflow rate can be used for judging the efficiency of root.Contribution of G. B. Pant University of Agriculture and Technology, Pantnagar-263145, India.