Shoot Fe Concentrations Research Articles

Effect of Iron Seed Dressing and Form of Nitrogen-Supply on Growth and Micronutrient Concentration in Shoots of Sorghum Grown in a Calcareous Sand Culture

ABSTRACT Seeds of sorghum [Sorghum bicolor (L.) Moench cv ‘Wrangler’] dressed with three increasing concentrations of an iron ethylenediamine-di-O-hydroxphenylacetic acid (FeEDDHA) product up to 480 mg Fe kg− 1 seed as a sole source of iron supply as well as a treatment without any dressing were grown for 19 days after germination in sand culture buffered to pH 8 by calcium carbonate. Nitrogen was supplied either as ammonium (NH4)-N or nitrate (NO3)-N, the former being supplemented with nitrapyrin (N Serve) to prevent nitrification. Chlorosis of the younger leaves was evident in all treatments except at the two higher levels of NH4-supplied plants. Dry matter yields of the shoots were raised only relatively slightly by the increasing levels of Fe supply and at each level the NH4 form was superior to that of NO3 -N. At the end of the growth period the pH of the sand around the roots had fallen by about 0.5 of a unit for NH4–fed plants and increased by about 0.2 of a unit for NO3-fed plants. At each level of Fe supply, NH4 nutrition approximately doubled the micronutrient [Fe, zinc (Zn), copper (Cu), manganese (Mn)] shoot concentrations and uptakes as compared with NO3-nutrition. For the NO3 –fed plants, increasing rates of Fe seed dressing had little effect on shoot Fe concentrations or uptakes, the concentration values determined (about 40 μ g g− 1 dry wt.) being below the range of critical deficiency concentration. Similarly concentrations of Mn were also in the deficiency range in the seed dressed NO3-fed plants (11–12 μ g g− 1 dry wt) so that in the NO3 treatments chlorosis may have resulted from a lack of Mn as well as Fe. Dressing sorghum seeds with Fe chelates in conjunction with NH4 fertilization supplemented with an inhibitor to prevent nitrification would appear to be a worthwhile approach to ensure an initial source of Fe to the young developing plant in the avoidance of iron-induced chlorosis in the growth of sorghum on high pH calcareous soils.

The leaf ionome as a multivariable system to detect a plant's physiological status

The contention that quantitative profiles of biomolecules contain information about the physiological state of the organism has motivated a variety of high-throughput molecular profiling experiments. However, unbiased discovery and validation of biomolecular signatures from these experiments remains a challenge. Here we show that the Arabidopsis thaliana (Arabidopsis) leaf ionome, or elemental composition, contains such signatures, and we establish statistical models that connect these multivariable signatures to defined physiological responses, such as iron (Fe) and phosphorus (P) homeostasis. Iron is essential for plant growth and development, but potentially toxic at elevated levels. Because of this, shoot Fe concentrations are tightly regulated and show little variation over a range of Fe concentrations in the environment, making them a poor probe of a plant's Fe status. By evaluating the shoot ionome in plants grown under different Fe nutritional conditions, we have established a multivariable ionomic signature for the Fe response status of Arabidopsis. This signature has been validated against known Fe-response proteins and allows the high-throughput detection of the Fe status of plants with a false negative/positive rate of 18%/16%. A "metascreen" of previously collected ionomic data from 880 Arabidopsis mutants and natural accessions for this Fe response signature successfully identified the known Fe mutants frd1 and frd3. A similar approach has also been taken to identify and use a shoot ionomic signature associated with P homeostasis. This study establishes that multivariable ionomic signatures of physiological states associated with mineral nutrient homeostasis do exist in Arabidopsis and are in principle robust enough to detect specific physiological responses to environmental or genetic perturbations.

Responses to Iron Limitation in Hordeum vulgare L. as Affected by the Atmospheric CO2 Concentration

Elevated atmospheric CO2 treatments stimulated biomass production in Fe-sufficient and Fe-deficient barley plants, both in hydroponics and in soil culture. Root/shoot biomass ratio was increased in severely Fe-deficient plants grown in hydroponics but not under moderate Fe limitation in soil culture. Significantly increased biomass production in high CO2 treatments, even under severe Fe deficiency in hydroponic culture, indicates an improved internal Fe utilization. Iron deficiency-induced secretion of PS in 0.5 to 2.5 cm sub-apical root zones was increased by 74% in response to elevated CO2 treatments of barley plants in hydroponics but no PS were detectable in root exudates collected from soil-grown plants. This may be attributed to suppression of PS release by internal Fe concentrations above the critical level for Fe deficiency, determined at final harvest for soil-grown barley plants, even without additional Fe supply. However, extremely low concentrations of easily plant-available Fe in the investigated soil and low Fe seed reserves suggest a contribution of PS-mediated Fe mobilization from sparingly soluble Fe sources to Fe acquisition of the soil-grown barley plants during the preceding culture period. Higher Fe contents in shoots (+52%) of plants grown in soil culture without Fe supply under elevated atmospheric CO2 concentrations may indicate an increased efficiency for Fe acquisition. No significant influence on diversity and function of rhizosphere-bacterial communities was detectable in the outer rhizosphere soil (0-3 mm distance from the root surface) by DGGE of 16S rRNA gene fragments and analysis of marker enzyme activities for C-, N-, and P-cycles.

Effects of Arbuscular Mycorrhizal Fungi on Growth and Yield of Cucumber Plants

In two pot experiments, cucumber (Cucumis sativus L. cv. Jinlu No. 3) seedlings were each inoculated with one of three arbuscular mycorrhizal fungi (AMF), Glomus mosseae, Glomus intraradices, or Glomus versiforme, or uninoculated. Seedling growth and weight of single fruit were investigated. The results indicated that growth of seedlings was significantly enhanced by G. mosseae, inhibited by G. versiforme, and not significantly influenced by G. intraradices. The dry weight of seedlings inoculated with G. mosseae was 1.2 times its counterparts. The concentrations of nitrogen (N) and phosphorus (P) in roots and magnesium (Mg), copper (Cu), and zinc (Zn) concentration in shoots were increased by inoculating the three AMF, and potassium (K) and iron (Fe) concentrations in shoots decreased significantly. The weights of single fruit of plants preinoculated with G. mosseae and G. versiforme were about 1.4 and 1.3 times higher than those from the uninoculated treatment, respectively.

Effect of peanut mixed cropping with gramineous species on micronutrient concentrations and iron chlorosis of peanut plants grown in a calcareous soil

To gain a better understanding of the mechanisms of improvement of iron nutrition of peanut (Arachis hypogaea L.) intercropped with maize (Zea mays L.) in calcareous soil, both greenhouse and field experiments were conducted to investigate the rhizosphere (phytosiderophores) effects from maize, barley, oats and wheat with different phytosiderophores release rates on iron nutrition and other micronutrients in calcareous soil. Six cropping treatments were examined in a greenhouse experiment: peanut grown separately in monoculture, normal peanut/maize intercropping (two genotypes: Danyu13, Zhongdan12), peanut/barley intercropping, peanut/oats intercropping, and peanut/wheat intercropping. Additionally, we investigated in a field experiment the same five cropping systems as the greenhouse experiment (maize/peanut intercropping not including Zhongdan12). Our results show that the chlorophyll and active Fe concentrations in the young leaves of the peanut in the intercropping system with different gramineous species were much higher than those of the peanut in monoculture. In greenhouse conditions, the Fe concentration in the shoots of peanut plants grown in the intercropping systems of two maize genotypes separately were 1.40–1.44, 1.47–1.64 and 1.15–1.42 times higher respectively than those of peanut plants grown in monocropping at 55, 60 and 70 days. In particular, the Fe concentration in shoots of peanut plants grown in the intercropping systems of barley, oats and wheat were not only higher than those in monocropping but also higher than those in peanut intercropped cropping with maize. In the field, the concentration of Fe in shoot of intercropped peanut plants in rows 1–3 from gramineous species were significantly higher than in monocropping at the flowering stage. Simultaneously with iron nutrition variation in peanut, Zn and Cu concentrations of intercropped grown peanut increased significantly compared to those in monocropping in the greenhouse experiment, and different intercropping treatments generally increased the Zn and Cu content in the shoot of peanut in the field. Systemic mechanisms may be involved in adaptation to nutrient stresses at the whole plant level. The study suggests that a reasonable intercropping system of nutrient efficient species should be considered to prevent or mitigate iron and zinc deficiency of plants in agricultural practice.

Al–Fe interactions and growth enhancement in Melastoma malabathricum and Miscanthus sinensis dominating acid sulphate soils

Plants growing in acid sulphate soils are subject to high levels of Al availability, which may have effects on the growth and distribution of these species. Although Fe availability is also high in acid sulphate soils, little is known about the effect of Fe on the growth of native plants in these soils. Two species dominating this soil type in Asia, viz. Melastoma malabathricum and Miscanthus sinensis were grown hydroponically in a nutrient solution with different concentrations of Al and Fe. Melastoma malabathricum is found to be sensitive to Fe (40 and 100 microm). Application of 500 microm Al, however, completely ameliorates Fe toxicity and is associated with a decrease of Fe concentration in shoots and roots. The primary reason for the Al-induced growth enhancement of M. malabathricum is considered to be the Al-induced reduction of toxic Fe accumulation in roots and shoots. Therefore, Al is nearly essential for M. malabathricum when growing in acid sulphate soils. In contrast, application of both Fe and Al does not reduce the growth of M. sinensis, and Al application does not result in lower shoot concentrations of Fe, suggesting that this grass species has developed different mechanisms for adaptation to acid sulphate soils.

Effect of iron supply and nitrogen form on growth, nutritional status and ferric reducing activity of spinach in nutrient solution culture

Abstract This study was carried out in order to give some information that could improve spinach nutritional status and productivity. In this paper, the effect of two N forms (N was added either as 100% nitrate or as 80% nitrate and 20% ammonium) and three Fe levels (0 μM Fe; 20 μM FeEDDHA; 3 μM FeEDDHA + 10 mM NaHCO3) on the growth, chlorosis symptoms and shoot nutrient element accumulation was studied in spinach plants (var. Viroflay), grown in hydroponics; six treatments and three harvests (at about 20 days interval each, until plants reached their commercial size) were applied in total. The results indicated that under conditions of Fe sufficiency (20 μM Fe), mixed N nutrition induced higher production of dry matter as well as improved Fe, Mn and Zn plant nutritional status. In plants grown under Fe deprivation (0 μM Fe), shoot Fe concentration was not significantly affected by the N form until the end of the experiment despite mixed N nutrition induced higher dry matter production up to harvest 2; plants grown under Fe deprivation and with mixed N nutrition presented also higher shoot Mn and Zn concentration. Under conditions of high concentration of bicarbonates and low level of Fe (3 μM Fe + 10 mM NaHCO3), the N form had not a significant influence on total dry matter production whereas shoot Fe and Mn accumulation in 100% NO3-fed plants was found to be significantly reduced compared to mixed N nutrition; regardless of the N form, those plants presented the least dry matter production, highest intensity of leaf chlorosis as well as highest root ferric reducing activity compared to plants grown under Fe deprivation.

Cadmium accumulation in Medicago sativa seedlings treated with salicylic acid

Growth parameters and cadmium accumulation were investigated in alfalfa seedlings treated with 10 μM salicylic acid (SA) at the beginning of seed imbibition. Shoot and root growths were accelerated by SA treatment and suppressed by Cd both in presence and absence of SA. Cd accumulation was stimulated by SA in alfalfa seedlings in dependence of the treatment duration. K, Mg, Ca and Fe contents in roots are decreased in the presence of Cd alone, while SA induces a decrease of Mg, Ca and Fe. Shoot K, Mg and Ca concentrations are increased by Cd only in the absence of SA, while SA induces also an increase of these concentrations, but only in the absence of Cd. High negative correlation of Cd concentration with K and Ca concentrations in root indicates a competition for the same carrier not regulated by SA. Positive correlation between Cd and Mg concentrations in shoots, which is decreased by SA pre-treatment, together with the increase of positive correlation between Cd and Fe concentrations in shoots under the influence of SA, indicates a possible mechanism of SA action through maintenance of ionic homeostasis.

Genotypic Difference in the Responses of Seedling Growth and Cd Toxicity in Rice ( Oryza sativa L.)

The experiment was carried out to study the genotypic difference in the responses of seed germination, growth and physiological characters of rice seedlings to Cd toxicity. The result showed that the germination was slightly stimulated under low Cd concentration (0.01–1.5 mM Cd), while severely depressed under higher Cd concentration (2.0 mM). Rice seedlings exposed to 0.01 mM Cd showed slight increases in plant height, root volume, biomass and chlorophyll concentration. These parameters were significantly reduced when Cd level in the medium was increased to 0.5 mM, and meanwhile corresponding increase in superoxide dismutase (SOD) and peroxidase (POD) activities, and MDA (malondialdehyde) content was observed. However, SOD and POD activities declined when plants were exposed to 1 mM Cd when compared with those under 0.5 mM Cd. Cadmium addition lowered Fe, Cu and Mn concentrations in roots and shoots. There was significant genotypic difference in the response of these parameters to Cd stress. Under Cd stress, Xiushui 110 had the least inhibition of growth and increase in MDA content, higher shoot Cd concentration, and greatest increase in POD and SOD activities, indicating its higher tolerance to Cd toxicity, while Bing 9914 had the greatest reduction of growth, and Zn, Cu, Fe, and Mn contents, but greatest increase in MDA content, and least increase in activities of antioxidative enzymes, indicating its sensitivity to Cd toxicity.

Effects of two iron sources on iron and cadmium allocation in poplar (Populus alba) plants exposed to cadmium

Effects of 10 microM cadmium (supplied as Cd nitrate) on the utilization and allocation of iron (Fe) were investigated in poplar (Populus alba L.) plants grown in nutrient solution with Fe(III)-EDTA or Fe(III)-citrate as the Fe source. The effects of Cd were also compared with those of Fe deprivation. The accumulation of Fe in roots was 10-fold higher in plants grown with Fe-citrate than with Fe-EDTA. Cadmium decreased leaf chlorophyll concentrations and photosynthetic rates, and these decreases were more marked in plants grown with Fe-citrate than with Fe-EDTA. In both Fe treatments, addition of Cd caused large increases in root and shoot apoplasmic and non-apoplasmic Cd contents and increases in root Fe content; however, Cd decreased shoot Fe content, especially in plants grown with Fe-citrate. New leaves of plants grown with Fe-citrate had small cellular (non-apoplasmic) Fe pools, whereas these pools were large in new leaves of plants grown with Fe-EDTA. Non-apoplasmic Cd pools in new leaves were smaller in plants grown with Fe-citrate than with Fe-EDTA, indicating that inactivation of non-apoplasmic Cd pools is facilitated more by Fe-EDTA than by Fe-citrate. In the presence of Cd, Fe-EDTA was also superior to Fe-citrate in maintaining an adequate Fe supply to poplar shoots. Differences in plant responses to Fe-EDTA and Fe-citrate may reflect differences in long-distance transport of Fe rather than in acquisition of Fe by roots.

QTLs for nutritional contents of rice seedlings (Oryza sativa L.) in solution cultures and its implication to tolerance to iron-toxicity

Iron toxicity is one of the major constraints for lowland rice production in highly weathered soils, which are widely distributed in tropics and subtropics and often lack macronutrients such as potassium (K) and phosphorus (P). To analyze the genetic factors for excess iron accumulation under K or P deficiency, a set of seedlings in F3 and F8 generations from an Oryza sativa cross between a japonica cultivar ‚Gimbozu’ and an indica cultivar ‚Kasalath’ were raised and exposed to nutritional stresses in a short period under nutritional solutions. In the F8 lines, contents of K, P, Fe, and Mg in dried shoots were measured. Quantitative trait loci (QTL) for the iron accumulation and related mineral contents in each plant were analyzed with composite interval mapping. QTLs for the Fe, P and Mg content in shoots were compared in the maps of F3 and F8. The QTLs for the Fe content in shoots varied in three types of nutritional conditions, but consistently indicated two overlapping regions on chromosome 3 and 4. The obtained QTLs were crosschecked with those reported before. Some of these QTLs were indicative of iron excluding the power of the root, which was expressed under reduced P content in solution.

Iron‐Manganese Interaction in Chickpea as Affected by Foliar and Soil Application of Iron in a Calcareous Soil

Soil application of inorganic source of iron (Fe) is not effective in correction of Fe deficiency in calcareous soils. The chelate form of Fe is, therefore, used for that purpose. Application of Fe‐chelate, however, may reduce crop yields due to the reduction of some nutrients availability including manganese (Mn). A greenhouse experiment was conducted in a completely randomized design to study the effect of Fe and Mn on the dry matter yield (DMY), interaction of Fe‐Mn, and concentration and uptake of other nutrients in chickpea (Cicer arietinum L. var. Pars). Treatments consisted of three Mn levels as Mn SO4·4H2O and four Fe levels (Foliar and soil application of FeSO4·7H2O and Fe‐EDDHA, respectively). Results showed that both foliar and soil application of Fe decreased mean shoot DMY, but Mn addition had no significant effect. Foliar application of Fe and addition of Mn increased mean shoot Fe concentration and uptake. Soil application of Fe and Mn increased mean shoot copper (Cu) concentration and uptake. Mean shoot zinc (Zn) concentration or uptake was not affected by Fe or Mn. These results showed that the suppressing effect of Fe on plant Mn concentration was not due to the reduction in root: shoot ratio, dilution effect, Fe toxicity or reduction in Mn uptake by root. Therefore, it may be concluded that the antagonistic effect of Fe on the translocation of Mn from root to shoot is the main reason for reduction in shoot Mn concentration in chickpea.

Nutrient attributes of tissues in relation to grazing in an evergreen sclerophyllous shrub ( Quercus coccifera L.) dominating vegetation in Mediterranean-type ecosystems

This study aims to identify differences in the nutrient attributes of Quercus coccifera (L.) tissues in response to grazing. For above-ground tissues, the analysis reveals a clear-cut distinction between samples from non-grazed, moderately grazed and overgrazed shrubs in relation to their nutrient attributes (N, P, Ca, Mg, K, and Fe concentrations). Variables with the greatest discriminatory power are those relating to the concentration of Mg, Fe and Ca in shoots. Analogous distinction is not recorded for below-ground tissues. The N and P concentrations in leaves (mg/g) are not affected by grazing while the amounts of Ca, Mg, Fe and N per unit leaf area, are significantly higher in the leaves of overgrazed shrubs.

Interaction of Cadmium and Four Microelements for Uptake and Translocation in Different Barley Genotypes

A hydroponic experiment was conducted in a greenhouse to study the interaction of cadmium (Cd) and four microelements [zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn)] for uptake, accumulation and distribution in barley during ontogenesis and their difference among genotypes. Cadmium addition to the medium not only significantly decreased Zn concentrations in all plant tissues, but also inhibited its translocation from roots to shoots, leading to higher root/shoot Zn ratio in Cd-treated plants. Cadmium addition also reduced Mn and Cu concentrations in kernels, roots and shoots and of Fe concentration in kernels and shoots. Significantly negative correlation was discovered between Zn, Cu, or Mn concentration and Cd concentration in different plant organs, suggesting the possibility of alleviating Cd accumulation in barley plants through application of these microelements on the Cd-contaminated soils. There was the significant difference among barley genotypes in uptake and translocation of Cd and four microelements.

Liming and Cultivars Affect Root Growth, Nodulation, Leaf to Stem Ratio, Herbage Yield, and Elemental Composition of Alfalfa on an Acid Soil

Soil acidity is one of the limiting factors affecting the production and sustainability of pastures and crops in many parts of the world. An on‐farm experiment was conducted in Australia to investigate the cultivar variation in alfalfa (lucerne) (Medicago sativa L.) with respect to soil acidity and response to applied lime. The experimental site was a brown sandy clay loam with a soil pH of 4.8 (1:5 calcium chloride). Ten cultivars (Hunter River, Hunterfield, Sceptre, Aurora, Genesis, Aquarius, Venus, PL90, PL55, and breeding line Y8804) were tested at two levels of lime (0 and 2 t ha−1). Lime application significantly increased the root growth, nodulation, leaf retention, leaf to stem ratio, herbage yield, and crude protein content of alfalfa. Liming had a significant effect on elemental composition of alfalfa shoots. Aluminum (Al) concentration was reduced from 93 mg kg−1 DM in nil lime treatment to 45 mg kg−1 DM in +lime treatment. Similarly, manganese (Mn) and iron (Fe) shoot concentrations were reduced from 74 mg kg−1 DM and 92 mg kg−1 DM to 59 mg kg−1 DM and 76 mg kg−1 DM, respectively. Liming significantly improved the calcium (Ca) concentration of shoots, while there was a little effect on phosphorus (P) and zinc (Zn) concentrations of alfalfa shoots. Cultivars had differential response to lime application. Response to lime application was greater in Y8804 and Aurora alfalfa where yield increased by 32% and 31%, while yield increase was 11–22% in other cultivars. Cultivars also differed significantly in root growth, nodulation, leaf drop, leaf to stem ratio, crude protein content, and elemental composition of shoots. Cultivars with better performance in no liming treatment had comparatively lower shoot Al, Mn, and Fe concentrations compared with other cultivars.

Amelioration of Manganese Toxicity in Young Rice Seedlings with Potassium

A hydroponic experiment was conducted in a controlled‐temperature glasshouse for 14 days to study the effect of additional potassium (K) on the amelioration of manganese (Mn) toxicity in young rice (Oryza sativa L. cv. Kakehashi) seedlings. Reduced growth, rolling of old leaves, brown spots and interveinal chlorosis on young leaves, and root browning were the main symptoms of Mn toxicity in plants grown with high Mn (1.0 mM) and adequate K (1.0 mM). Application of additional K (10 mM) to the nutrient solution increased chlorophyll concentration and dry matter yields of plants grown in high Mn, but did not restore dry matter accumulation to the level achieved in the control plants. Plants grown in 1.0 mM Mn and 10 mM K had lower tissue Mn concentration on a dry matter basis than plants grown in 1.0 mM Mn and 1.0 mM K and did not show leaf injury symptoms, but still showed root browning; however, the accumulation (per plant basis) of Mn was approximately the same, indicating that additional K increased the tolerance of the plant to high Mn. The concentration and accumulation of iron (Fe) in shoots of plants grown at 1.0 mM K with 1.0 mM Mn was lower than in the control plants, indicating an inhibition of Fe translocation to shoots by high Mn. Additional K increased both concentration and accumulation of Fe in shoots and roots of plants grown in high Mn. The higher phosphorus (P), K, zinc (Zn), and copper (Cu) concentrations in shoots and roots of plants grown in 1.0 mM Mn and 1.0 mM K could be a concentration effect because of severe growth reduction, while lower calcium (Ca) and magnesium (Mg) concentrations were probably due to competition with Mn at the absorption sites. Additional K further decreased Ca and Mg concentrations, indicating possible interference of K with the absorption and physiological availability of Ca and Mg. Additional K increased K concentrations and decreased P, Cu, and Zn concentrations in shoots and roots of plants grown with high Mn. These results suggest that additional K can partially alleviate the symptoms of Mn toxicity and Mn‐induced Fe deficiency in rice seedlings and significantly improve plant growth.

Phenotypic Characterization of Microbes in the Rhizosphere of Alyssum murale

Abstract Metal hyperaccumulator plants like Alyssum murale are used for phytoremediation of Ni contaminated soils. Soil microorganisms are known to play an important role in nutrient acquisition for plants, however, little is known about the rhizosphere microorganisms of hyperaccumulators. Fresh and dry weight, and Ni and Fe concentrations in plant shoots were higher when A. murale was grown in non‐sterilized compared to sterilized soils. The analysis of microbial populations in the rhizosphere of A. murale and in bulk soils demonstrated that microbial numbers were affected by the presence of the plant. Significantly higher numbers of culturable actinomycetes, bacteria and fungi were found in the rhizosphere compared to bulk soil. A higher percent of Ni‐resistant bacteria were also found in the rhizosphere compared to bulk soil. Percentage of acid producing bacteria was higher among the rhizosphere isolates compared to isolates from bulk soil. However, proportions of siderophore producing and phosphate solubilizing bacteria were not affected by the presence of the plant. We hypothesize that microbes in the rhizosphere of A. murale were capable of reducing soil pH leading to an increase in metal uptake by this hyperaccumulator.

Phenotypic characterization of microbes in the rhizosphere of alyssum murale

Metal hyperaccumulator plants like Alyssum murale are used for phytoremediation of Ni contaminated soils. Soil microorganisms are known to play an important role in nutrient acquisition for plants, however, little is known about the rhizosphere microorganisms of hyperaccumulators. Fresh and dry weight, and Ni and Fe concentrations in plant shoots were higher when A. murale was grown in non‐sterilized compared to sterilized soils. The analysis of microbial populations in the rhizosphere of A. murale and in bulk soils demonstrated that microbial numbers were affected by the presence of the plant. Significantly higher numbers of culturable actinomycetes, bacteria and fungi were found in the rhizosphere compared to bulk soil. A higher percent of Ni‐resistant bacteria were also found in the rhizosphere compared to bulk soil. Percentage of acid producing bacteria was higher among the rhizosphere isolates compared to isolates from bulk soil. However, proportions of siderophore producing and phosphate solubilizing bacteria were not affected by the presence of the plant. We hypothesize that microbes in the rhizosphere of A. murale were capable of reducing soil pH leading to an increase in metal uptake by this hyperaccumulator.

Alleviation of manganese toxicity and manganese-induced iron deficiency in barley by additional potassium supply in nutrient solution

Barley plants were grown hydroponically at two levels of K (3.0 and 30 mm) and Fe (1.0 and 10 μm) in the presence of excess Mn (25 μm) for 14 d in a phytotron. Plants grown under adequate K level (3.0 mm) were characterized by brown spots on old leaves, desiccation of old leaves, interveinal chlorosis on young leaves, browning of roots, and release of phytosiderophores (PS) from roots. These symptoms were more pronounced in the plants grown under suboptimal Fe level (1.0 p,M) than in the plants grown under adequate Fe level (10 μm). Plants grown in 10 μm Fe with additional K (30 mm) produced a larger amount of dry matter and released less PS than the plants grown under adequate K level (3.0 mm), and did not show leaf injury symptoms and root browning. On the other hand, the additional K supply in the presence of 1.0 μM Fe decreased the severity of brown spots, prevented leaf desiccation, and increased the leaf chlorophyll content, which was not sufficient for the regreening of chlorotic leaves. These results suggested that the additional K alleviated the symptoms of Mn toxicity depending on the Fe concentration in the nutrient solution. The concentration (per g dry matter) and accumulation (per plant) of Mn in shoots and roots of plants grown in 10 μm Fe and 30 mm K were much lower than those of the plants grown in 10 μm Fe and 3.0 mm K, indicating that additional K repressed the absorption of Mn. The concentration and accumulation of Fe in the shoots and roots of the plants grown in 10 μm Fe and 30 mm K were higher than those of the plants grown in 10 μm Fe and 3.0 mm K, indicating that the additional K increased the absorption of Fe under excess Mn level in the nutrient solution. The release of PS, chlorophyll content, and shoot Fe concentration were closely correlated.

Effects of Cd and Pb in sugar beet plants grown in nutrient solution: induced Fe deficiency and growth inhibition.

Effects of Cd and Pb toxicity were investigated in sugar beet (Beta vulgaris L.) grown in hydroponics under growth-chamber-controlled conditions. Chemical speciation calculations were used to estimate the chemical species in equilibrium. Cd, used as chloride salt or chelated to EDTA, decreased fresh and dry mass of both root and shoot, and increased root / shoot ratios. Plants developed few brownish roots with short laterals. Cd decreased N, P, Mg, K, Mn, Cu and Zn uptake, and facilitated Ca uptake. Leaves of plants treated with 10 or 50 μM Cd-EDTA and 10 μM CdCl2 developed symptoms of Fe deficiency. These symptoms included decreased leaf chlorophyll (Chl) and carotenoid concentrations, increased carotenoid / Chl and Chl a/b ratios, de-epoxidation of violaxanthin cycle pigments, and decreased photosynthetic rates and PSII efficiency. Plants treated with 50 μM CdCl2, however, had decreased growth but did not show marked leaf Fe-deficiency symptoms. All Cd treatments increased Fe(III)-chelate reductase activity in root tips, although Fe concentrations in shoots were similar to those found in control plants. Pb chelated with EDTA induced visual symptoms only at concentrations of 2 mM. Leaves of Pb-treated plants remained green and their edges were rolled inwards. Pb increased root fresh and dry mass with no changes in shoot mass, therefore increasing the root / shoot ratio. Changes in plant nutrient concentrations with Pb were only minor, although leaf Cu levels approached critical deficiency levels. No symptoms of Fe deficiency were apparent in leaves. Root tips of Pb-treated plants, however, had increased Fe(III)-chelate reductase activities.