Aluminum stress on sorghum growth and nutrient relationships

Summary Sorghum plants were grown in the greenhouse in modified Steinberg nutrient solution containing ten Al rates (0 to 297 μM) and harvested 28 days after transplanting. Top and root dry weight were not affected by added Al up to 74 μM; but decreased sharply at concentration of 148 μM and greater. Aluminum concentrations in blade 1 (recently matured blade) and plants remained constant from 0 to 297 μM added Al. Root Al concentration increased as added Al increased. No correlation existed between top dry weight and Al concentration in blade 1 or in plant. Root Al concentration was related to top dry weight and root dry weight to estimate the Al critical toxicity level. The Al critical toxicity levle in the root was 54 mmol kg⁻¹ root dry weight basis for either top or root dry weight. In blade 1 Cu concentration negatively correlated with Al while Fe and P were positively correlated. In roots Ca, Mg, Mn and Fe concentrations were negatively correlated with Al while Zn, Cu, P, and K were positively correlated with Al concentration.     

Response of plants to calcium concentration in flowing solution culture with chloride or sulphate as the counter-ion

Summary Solution calcium concentrations required for the growth of a range of plant species, including both monocotyledons and dicotyledons, were determined in two experiments in which plants were grown in flowing solution culture at constantly maintained calcium concentrations ranging from 0.5 to 3000 μM. Calcium chloride was used as the calcium source in the first experiment, calcium sulphate was used in the second. At calcium concentrations of 10 μM and below, all species developed calcium deficiency symptoms. The severity of the deficiency was more pronounced in the dicotyledons than in the monocotyledons. However, cassava was much more tolerant than all other dicotyledons and equally as tolerant as rice, the most tolerant monocotyledon. Solution calcium concentrations required for 90% of maximum yield were generally lower for monocotyledons (3 to 20 μM) than for dicotyledons (7 to 720μM) when calcium chloride was used as the calcium source. When calcium sulphate was used, 7 out of 11 species, including 3 monocotyledons, required external calcium concentrations of 1200 μM and above. The results are discussed in relation to effects of solution composition and the choice of counter-ions on plant response to calcium and other macronutrient cations. It is concluded that yield depressions due to toxicity of excesses of chloride, and possibly other counter-ions, can lead to serious underestimation of limiting external cation concentrations for plant growth.     

Comparison of plant uptake and plant toxicity of various ions in wheat

The effects of varying solution concentrations of manganese (Mn), zinc (Zn), copper (Cu), boron (B), iron (Fe), gallium (Ga) and lanthanum (La) on plant chemical concentrations, plant uptake and plant toxicity were determined in wheat (Triticum aestivum L.) grown in a low ionic strength (2.7×10^–3 M solution culture). Increasing the solution concentration of Mn, Zn, Cu, B, Fe, Ga and La increased plant concentrations of that ion. Asymptotic maximum plant concentrations were reached for Zn (10 mg kg DM^–1 in the roots), Ga (2 mg kg DM^–1 in the tops and 18 mg kg DM^–1 in the roots) and La (0.4 mg kg DM^–1 in the tops and 4 mg kg DM^–1 in the roots). Plant ion concentrations were, on average, 3 times higher in the roots than the tops for Mn and Zn, 7 times for Cu, 9 times for Fe, 12 times for Ga and 15 times for La. In contrast, B concentrations were higher in the tops than the roots by, on average, 2 times. The estimated toxicity threshold (plant concentration at which a rapid decrease in yield occurred) in the tops was 0.4 mg g DM^–1 for B, 2 for Zn, 0.075 for Cu and 0.09 for La and in the roots 0.2 mg g DM^–1 for B, 5 for Zn, 0.3 for Cu and 3 for La. Plant uptake rates of the ions (as estimated by the slope of the relationship between solution ion concentrations and plant ion concentrations) was in the order B 250 mg kg DM^–1 M ^–1). Plant toxicity was estimated as the reciprocal of the plant concentration that reduced yield by 50% (change in relative yield per mg ion kg DM^–1). The plant toxicity of the ions tested was in the order Mn相似文献   

Effect of exogenous amino acids on Cu uptake and translocation in maize seedlings

This study aimed to assess the effects of four contrasting proteinogenic amino acids on copper (Cu) uptake and translocation in maize (Zea mays L.) seedlings grown in a modified Hoagland solution. Glycine, aspartic acid and lysine at three concentrations (10, 25 and 100 μM) did not have any significant effect on Cu uptake and translocation in maize seedlings over a two-day experimental period. However, cysteine (a reductive amino acid) at the three concentrations increased very significantly (P < 0.01) Cu accumulations in the root symplast and the shoots of maize seedlings in comparison to the control. Cu uptake in the whole plant and Cu translocation from root to shoot were also increased in the cysteine treatments. In the 25 μM cysteine treatment, where cysteine was in moderate excess, the Cu uptake in the whole plant and Cu translocation from root to shoot were significantly (P < 0.01) higher than those of the 10 or 100 μM cysteine treatments, where the concentration of cysteine was equivalent to that of Cu(II) or in great excess according to the stoichiometry of the redox reaction of cysteine with Cu(II). It is hypothesized that the cysteine-induced oxidation state alteration from Cu(II) to Cu(I) could be responsible for the increased Cu uptake and Cu translocation, on the ground that Cu(I), as free cuprous ion or cysteine cuprous complex, may be more available to maize roots than Cu(II).     

Effect of Cu Toxicity on Growth of Cowpea (Vigna unguiculata)

Accurate determination of the rhizotoxicity of Cu in dilute nutrient solutions is hindered by the difficulty of maintaining constant, pre-determined concentrations of Cu (micromolar) in solution. The critical Cu²⁺ activity associated with a reduction in the growth of solution-grown cowpea (Vigna unguiculata (L.) Walp. cv. Caloona) was determined in a system in which Cu was maintained constant through the use of a cation exchange resin. The growth of roots and shoots was found to be reduced at solution Cu²⁺ activities ≥1.7 μM (corresponding to 90% maximum growth). Although root growth was most likely reduced due to a direct Cu²⁺ toxicity, it is considered that the shoot growth reduction is attributable to a decrease in tissue concentrations of K, Ca, Mg, and Fe and the formation of interveinal chlorosis. At high Cu²⁺ activities, roots were brown in color, short and thick, had bent root tips with cracking of the epidermis and outer cortex, and had local swellings behind the roots tips due to a reduction in cell elongation. Root hair growth was reduced at concentrations lower than that which caused a significant reduction in overall root fresh weight.     

Manganese and iron interactions on their uptake and distribution in soybean (Glycine max (L.) Merr.)

Summary The uptake and distribution of iron and manganese were studied in a manganese-sensitive soybean cultivar (‘Bragg’) grown over a range of supply levels of these nutrients in solution culture. At high (90 and 275 μM) manganese levels, increasing the iron concentration in solution from 2 to 100 μM partially overcame the effects of manganese toxicity. Interactions between manganese and iron occurred for dry matter yields, rate of Mn absorption by the roots, and the proportions of manganese and iron transported to the tops. No interaction was observed for the rate of root absorption of iron. The percentage distribution of manganese in the plant top increased with increasing iron, despite a reduced rate of Mn uptake. On the other hand, iron uptake was independent of solution Mn concentration and increased with increasing solution Fe. Also more iron was retained in the roots at high Mn and/or Fe levels in solution. Concentrations of manganese and iron in roots, stems and individual leaves were affected independently by the manganese and iron supplyi.e. without any interaction occurring between the two elements. In general, the concentration in a plant part was related directly to the solution concentration. Symptoms resembling iron deficiency correlated poorly with leaf Fe concentrations whereas high levels of manganese were found in leaves displaying Mn toxicity symptoms.     

Effect of pH and nitrogen source on aluminium tolerance of rye (Secale cereale L.) and yellow lupin (Lupinus luteus L.)

Soluble aluminium (Al) is a major factor limiting plant growth in acid mineral soils. Aluminium concentrations in soil solutions are mainly determined by soil pH. However, pH also affects the ratio between activities of protons and cationic Al species and the equilibrium between mono-and polynuclear hydroxy-Al species. The phytotoxicity of these species is not yet clear. The objective of the present study was to clarify the role of minor changes of pH in the rhizosphere on Al phytotoxicity in two Al-tolerant plant species by direct control of the pH in the nutrient solution (4.1, 4.3, 4.5) and in addition by varying the pH in the root apoplast using either nitrate or ammonium as N source. The plants were grown in solution culture at constant external pH. Whereas the Al-sensitive plant species barley and horse bean were damaged at very low Al supplies (1.85 μM and 9.3 μM respectively), 222 μM had to be applied to rye and yellw lupin for a comparable inhibition of root elongation. Yellow lupin was initially severely inhibited in root growth by Al, but then gradually recovered from this ‘Al shock’ within 3 days. In contrast to lupin, rye was hardly affected by Al initially, and it took about 16 h until maximum inhibition of root elongation. In the presence of nitrate, raising the pH from 4.1 to 4.5 aggravated root-growth depression by Al in rye and lupin. Whereas rye roots were severely damaged by ammonium especially at low pH, lupin was rather indifferent to the N source. Aluminium toxicity was less severe in presence of ammonium compared to nitrate N. This effect was less clear with rye at lower pH, because of it's higher proton sensitivity compared to lupin. Less Al injury at lower pH and in presence of ammonium was related to lower Al concentrations in the 1 cm root tips. The results are compatible with data showing high phytotoxicity of mononuclear and polynuclear hydroxy-Al species. However, they could also be interpreted in the light of proton amelioration of Al toxicity owing to competition for Al-sensitive binding sites in the root apoplast.     

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl₂ and 0–2 µM CuCl₂. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.     

Factors affecting aluminium sorption by calcium pectate

Extracellular processes, particularly the adsorption of aluminium (Al) by pectate in the cell wall, have been proposed as important in the expression of Al toxicity to plant roots. In vitro studies were conducted on the effects of Al concentration (generally ≤ 32 μM), calcium (Ca) concentration (0.05 to 10 mM) and pH (3.2 to 5.4) on Al sorption by Ca pectate. There was a rapid reaction between Al and Ca pectate, there being no difference in Al remaining in solution after reaction times of 1 to 16 min, and only a slight decrease after 24 h. Increased Al concentration in solution increased linearly the sorption of Al by Ca pectate, with 70 to 84% of the Al originally in solution sorbed with ≤32 μM Al. In contrast, Al sorption decreased with increased Ca concentration in solution, and as pH decreased from 5.4 to 3.2. Only ≤30% of the sorbed Al was desorbed after 1 h by 1 mM CaCl₂, 10 mM CaCl₂ or 1 mM HCl. The amount of Al desorbed increased with a desorption period of 5 h, particularly with 1 mM HCl. These studies suggest that Al sorbed by Ca pectate in root cell walls is in equilibrium with Al in solution, and that Al toxicity is associated with the strong binding between Al and Ca pectate external to the cytoplasm.     

Iron Enhances Aluminum-induced Leaf Necrosis and Plant Growth Inhibition in Eucalyptus camaldulensis

The combined effects of excess Fe and Al on Eucalyptus camaldulensis Dehnh. were studied by investigating time course and visible symptoms of leaf necrosis, plant biomass, the status of some antioxidants and pigments and nutrient concentrations. Seedlings were grown hydroponically in nutrient solutions containing 0 or 500 μM AlCl₃, each with a FeSO₄ range of 1, 12 and 120 μM at pH 4.2. Leaf necrosis and plant growth inhibition were induced by Al and enhanced by the increase in Fe concentration. The process from the first appearance of necrotic spots to leaf death (shedding) of a leaf proceeded from a few days to about 20 days after the leaf had fully expanded. Either 120 μM Fe without Al or Al reduced plant growth to a similar extent but 120 μM Fe without Al did not cause leaf necrosis. In leaves, excess Fe (12 and 120 μM) without Al reduced concentration of ASC and GSH, while concentration of Fe, DHA and GSSG and DHA:ASC and GSSG:GSH ratios tended to increase with the increase in Fe concentration in treatment solution with or without Al. At 1 μM Fe, Al increased concentration of DHA and DHA:ASC and GSSG:GSH ratios. Catalase activity in leaves reduced with the increase in leaf Al concentration. At 1 μM Fe, Al greatly reduced concentrations of Fe and chlorophylls in leaves but increase two times Fe concentration in stems. These suggest that the enhancement effects of Fe on Al-induced leaf necrosis and plant growth inhibition can be discussed in context of the excess Fe itself weakens antioxidant capability of ASC–GSH cycle in leaves and greatly reduces plant growth; and the increase in Fe accumulation in stems is involved in Al-induced leaf chlorosis.     

Manipulation of the morphogenetic pathways of Lilium longiflorum transverse thin cell layer explants by auxin and cytokinin

Summary Excised tissues from transverse young stem sections of Lilium longiflorum were cultured on Murashige and Skoog medium supplemented with growth regulators at various concentrations. After 45 d in culture, the presence of α-naphthaleneacetic acid (NAA) in the culture medium at 5.4 μM resulted in bulblet formation while 2,4-dichlorophenoxyacetic acid (2,4-D) at 2.2 μM resulted in root formation. The presence of IBA (indole-3-butyric acid) in the culture medium at 1.0 μM resulted in shoot formation while plantlet formation occurred when IBA was added at a concentration of 2.0 μM. When 1-phenyl-3-(1,2,3-thiadiazol-5-yl)-urea (TDZ) was added to the culture medium at 1.1 μM, protocorm-like bodies (PLBs) formed, while 2.2 μM resulted in shoot formation (on abaxial and adaxial surfaces). The presence of NAA and TDZ in the culture medium at 5.4 μM and 0.4, 1.1 or 2.2 μM, respectively, resulted in somatic embryo formation while NAA- and 6-benzylaminopurine-(BA) containing culture medium formed callus or bulblets. The establishment of different regeneration systems when explants are exposed to various growth regulators demonstrates that the choice of growth regulator combinations and concentrations are of significance in determining the morphogenetic response and plant regeneration capacity.     

Release of phenols from Lupinus albus L. roots exposed to Cu and their possible role in Cu detoxification

The mechanisms enabling plants to tolerate high concentrations of available Cu in their rhizosphere are still poorly understood. To better understand the mechanisms involved, Lupinus albus L. (white lupin) was grown over 40 days in a hydroponic system compelling roots to develop under sterile conditions in the presence of a nutrient solution containing 0.5, 20 or 62 M Cu. The following parameters were investigated in detail: low molecular weight phenols in nutrient solution (colorimetric assay), high molecular weight phenols in roots and in solution (HPLC-MS, HPLC-UV), pH, redox potential in solution (electrochemistry) and Cu distribution in the plant (AAS) as well as in apical root sections (EDX microanalysis). Finally, in vitro adsorption studies using voltammetry were conducted to evaluate the Cu adsorption behaviour of different phenolic compounds. When exposed to 62 M Cu, biomass production of white lupin was strongly reduced. Plants grown in the presence of 20 M Cu had a similar dry matter production compared to the control plants grown in a 0.5 M Cu solution. However, an increased release of soluble and high molecular weight phenols into the solution was observed. The concentration of polyphenolic compounds in the roots (particularly isoflavonoids like genistein and genistein-(malonyl)-glucoside) was significantly higher for lupins grown in a 20 M Cu solution compared to the control plants. As shown by an in vitro adsorption study, these phenolic compounds can bind Cu ions. In addition, plants exposed to 20 and 62 M Cu cumulated high Cu amounts in root cell walls whereas only low amounts reached the symplasm. Therefore, it is proposed that the complexation of Cu²⁺ ions in the rhizosphere and in the roots apoplasm by phenolic compounds could alleviate Cu-mediated toxicity.     

External phosphorus requirements of five tropical grain legumes grown in flowing-solution culture

Summary Five tropical grain legume species were grown for periods from 4 to 20 days in flowing-solution culture at 7 maintained phosphorus (P) concentrations, ranging from 0.25 μM to 16 μM. Critical external P requirements were 0.8 μM for cowpea cv. Vita 4 and soybean cv. Fitzroy, 1.0 μM for pigeon pea cv. Royes, 2.0 μM for mungbean cv. Regur and 3.0 μM for guar cv. Brooks. Plant responses to P deficiency included reduced growth rate, increased root percentage, and increased P uptake potential. The long-term P uptake rates of guar plants were lower than those of the other species at each external P concentration. Guar plants had a low P uptake potential as indicated by short-term^32CP-labelled uptake rate studies from 15 μM P solutions. Cowpea by contrast had high short-term uptake rates indicating a high P uptake potential.     

The toxicity of cadmium to barley plants as affected by complex formation with humic acid

An ‘alternating solution’ culture method was used to study the effects of chloride ions and humic acid (HA) on the uptake of cadmium by barley plants. The plants were transferred periodically between a nutrient solution and a test solution containing one of four levels of HA (0, 190, 569 or 1710 μg cm⁻³) and one of five levels of Cd (0, 0.5, 1.0, 2.5 or 5.0 μg cm⁻³) in either a 0.006M NaNO₃ or 0.006M NaCl medium. Harvest and analysis of shoots and roots was after nineteen days. The distribution of Cd in the test solutions between Cd²⁺, CdCl⁺ and HA-Cd was determined in a separate experiment by dialysis equilibrium. In the nitrate test solutions Cd uptake was clearly controlled by Cd²⁺ concentration and was therefore reduced by HA complex formation. In the absence of HA, chloride suppressed Cd uptake indicating that Cd²⁺ was the preferred species. However complex formation with Cl⁻ enhanced uptake when HA was present because of an increase in the concentration of inorganic Cd species relative to the nitrate system. The ratio root-Cd/shoot-Cd remained at about 10 across a wide range of shoot-Cd concentrations, from about 3 μg g⁻¹ (sub-toxic) up to 85 μg g⁻¹ (80% yield reduction). The ability of the barley plants to accumulate ‘non-toxic’ Cd in their roots was thus very limited. Humic acid also had no effect on Cd translocation within the plant and the root/shoot weight ratio did not vary with any treatment. At shoot-Cd concentrations in excess of 50 μg g⁻¹, K, Ca, Cu and Zn uptake was reduced, probably the result of root damage rather than a specific ion antagonism. The highest concentration of HA also lowered Fe and Zn uptake and there was a toxic effect with increasing HA concentration at Cd=0. However the lowest HA level, comparable with concentrations found in mineral soil solutions, only reduced yield (in the absence of Cd) by <5% while lowering Cd uptake across the range of Cd concentrations by 66%–25%.     

Mobilization of Cu and Zn by root exudates of dicotyledonous plants in resin-buffered solutions and in soil

It has been frequently suggested that root exudates play a role in trace metal mobilization and uptake by plants, but there is little in vivo evidence. We studied root exudation of dicotyledonous plants in relation to mobilization and uptake of Cu and Zn in nutrient solutions and in a calcareous soil at varying Cu and Zn supply. Spinach (Spinacia oleracea L.) and tomato (Lycopersicon esculentum L.) were grown on resin-buffered nutrient solutions at varying free ion activities of Cu (pCu 13.0–10.4) and Zn (pZn 10.1–6.6). The Cu and Zn concentrations in the nutrient solution increased with time, except in plant-free controls, indicating that the plant roots released organic ligands that mobilized Cu and Zn from the resin. At same pCu, soluble Cu increased more at low Zn supply, as long as Zn deficiency effects on growth were small. Zinc deficiency was observed in most treatment solutions with pZn ≥ 9.3, but not in nutrient solutions of a smaller volume/plant ratio in which higher Zn concentrations were observed at same pZn. Root exudates of Zn-deficient plants showed higher specific UV absorbance (SUVA, an indicator of aromaticity and metal affinity) than those of non-deficient plants. Measurement of the metal diffusion flux with the DGT technique showed that the Cu and Zn complexes in the nutrient solutions were highly labile. Diffusive transport (through the unstirred layer surrounding the roots) of the free ion only could not explain the observed plant uptake of Cu and of Zn at low Zn²⁺ activity. The Cu and Zn uptake by the plants was well explained if it was assumed that the complexes with root exudates contributed 0.4% (Cu) or 20% (Zn) relative to the free ion. In the soil experiment, metal concentrations and organic C concentrations were larger in the solution of planted soils than in unplanted controls. The SUVA of the soil solution after plant growth was higher for unamended soils, on which the plants were Zn-deficient, than for Zn-amended soils. In conclusion, root exudates of dicotyledonous plants are able to mobilize Cu and Zn, and plants appear to respond to Zn deficiency by exuding root exudates with higher metal affinity.     

Aluminum-mycorrhizal interactions in the physiology of pitch pine seedlings

Aluminum (Al) in the rhizosphere adversely affects plant nutrition and growth. Although many conifer species, and pitch pine (Pinus rigida) in particular, have evolved on acidic soils where soluble Al is often high, controlled environment studies often indicate that Al interferes with seedling growth and nutrient relations. Under normal field conditions, conifer roots grow in a symbiotic relationship with ectomycorrhizal fungi, and this association may modulate the effects of Al on root physiology. To investigate the influence of mycorrhizal infection on Al toxicity, pitch pine seedlings were grown with or without the ectomycorrhizal symbiont Pisolithus tinctorius and were exposed to low levels of Al in sand culture. Aluminum at 50 μM reduced nonmycorrhizal seedling growth and increased foliar Al concentrations, but did not alter photosynthetic gas exchange or other aspects of seedling nutrition. Nonmycorrhizal seedlings exposed to 200 μM Al exhibited decreased growth, increased transpiration rates, decreased water use efficiency, increased foliar Al and Na levels, and reduced foliar P concentrations. Seedlings inoculated with P. tinctorius exhibited unaltered growth, physiological function, and ionic relations when exposed to Al. The fungal symbiont evidently modulated ionic relations in the rhizosphere, reducing Al-P precipitation reactions, Al uptake, and subsequent root and shoot tissue Al exposure.     

The effects of low concentrations of aluminium on the growth and uptake of nitrate-N by white clover

Summary The effects of aluminium (Al³⁺) at concentrations of 0, 25, 50 and 100 μM on the growth of white clover, dependent upon N supplied as NO ₃ ⁻ , were examined in flowing solution culture. Plants were established with a normal nutrient supply for 7 weeks and then grown with carefully controlled pH (at 4.5) and P concentrations, and with 0, 25, 50 or 100 μM Al³⁺ for a further three weeks. There were rapid visual effects (i.e. symptoms of P deficiency and reduction in root extension) and the dry weights of shoots and roots were reduced at 50 and 100 μM. Less than 10% of Al absorbed from solution was transported to the shoots. The uptake of P, and its transport between roots and shoots, were reduced in plants grown with Al. The uptake of NO ₃ ⁻ stopped immediately after the introduction of 50 or 100 μM Al, and was significantly reduced at 25 μM after three weeks. During a second phase of the experiment, plants previously grown at 0, 25, 50 and 100 μM Al, were grown for a further 2 weeks either with NO ₃ ⁻ (with and without 50 μM Al³⁺) or without NO ₃ ⁻ but with inoculation by Rhizobia (and with or without 50 μM Al³⁺). The effects of the previous treatments with Al on N uptake were small during the second phase, but uptake by all plants was restricted when Al was present. Inoculation did not result in nodulation in the second phase when Al³⁺ was present in the solution, but Al already in the plant from the first phase did not prevent nodulation in the absence of Al during the second phase.     

Factors controlling equilibrium boron (B) concentration in nutrient solution buffered with B-specific resin (Amberlite IRA-743)

In conventional solution culture where boron (B) is added as boric acid, fluctuating external B supply often produces confounding and ill-defined physiological and biochemical responses in plants, especially when grown at deficient and marginal B supply. Our previous studies proposed the use of the B-specific resin – Amberlite IRA-743 to develop a B-buffered solution culture. The present study aims to evaluate crucial factors determining equilibrium B concentrations in nutrient solution buffered with the B-loaded resin, including the B loading of the resin, pH in the nutrient solution and B removal from the solution. The equilibrium B concentrations in nutrient solution were determined by both the amount of B sorbed by the resin and the solution pH. At pH 6.05±0.05, the relationship between the resin B content and equilibrium B concentration in the nutrient solution is closely described by the equation: Y = 18.8 X^1.457 [ where, Y = equilibrium B concentration (μM) in nutrient solution and X = B content of the resin (mg B g⁻¹ moist resin)]. However, at a given resin B content, lowering solution pH from 7 to 4 significantly increased B concentrations in solution through the release of B from the solid phase of the resin beads. The B-loaded resin was capable of maintaining stable B concentrations in the nutrient solutions, ranging from deficient to marginally adequate B concentrations for dicot species. In conclusion, B concentrations ranging from 0.05 to 11 μM, were buffered for 5 days with the resin loaded with 0.004 – 0.691 mg B g⁻¹ moist resin in the nutrient solution. Precise pH control in the nutrient solution is critical for the success of a B-buffered solution culture study. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of aluminium on nodulation of two Stylosanthes species grown in nutrient solution

Summary Effects of three solution aluminium concentrations (0, 25 and 100 M) on nodulation ofStylosanthes hamata andStylosanthes scabra inoculated with Rhizobium CB 756 were studied using nutrient solution culture. Aluminium strongly affected nodulation by delaying nodule appearance and reducing the number and dry weight of nodules in both species. The effects of aluminium toxicity on nodulation were more pronounced inStylosanthes scabra than inStylosanthes hamata. These effects of aluminium on nodulation occurred before any significant effect of aluminium on top growth, root growth or root elongation. A plant transfer experiment suggested that aluminium interfered with root infection and/or nodule initiation in both species. The detrimental effect of aluminium on nodulation appeared to be associated with a reduction in lateral root density, thus decreasing the potential number of sites for root infection and nodule formation.