Efficient iron plaque formation on tea(Camellia sinensis) roots contributes to acidic stress tolerance

Tea plants grow in acidic soil, but to date, their intrinsic mechanisms of acidic stress tolerance have not been elucidated. Here, we assessed the tea plant response to growth on NHt4 nutrient media having different p H and iron levels. When grown in standard NHt4 nutrient solution(iron insufficient, 0.35 mg Là1 Fe2t), tea roots exhibited significantly lower nitrogen accumulation, plasma membrane Ht-ATPase activity, and protein levels; net Htefflux was lower at pH 4.0 and 5.0 than at pH 6.0. Addition of30 mg Là1 Fe2t(iron sufficient, mimicking normal soil Fe2tconcentrations) to the NHt4 nutrient solution led to more efficient iron plaque formation on roots and increased root plasma membrane Ht-ATPase levels and activities at p H 4.0 eland 5.0, compared to the p H 6.0 condition. Furthermore,plants grown at pH 4.0 and 5.0, with sufficient iron,exhibited significantly higher nitrogen accumulation than those grown at pH 6.0. Together, these results support the hypothesis that efficient iron plaque formation, on tea roots, is important for acidic stress tolerance. Furthermore,our findings establish that efficient iron plaque formation is linked to increased levels and activities of the tea root plasma membrane Ht-ATPase, under low pH conditions.     

Understanding nucleosomal histone and DNA interactions: a biophysical study

Histones are associated with DNA to form nucleosome essential for chromatin structure and major nuclear processes like gene regulation and expression. Histones consist of H1, H2A, H2B and H3, H4 type proteins. In the present study, combined histones from calf thymus were complexed with ct DNA and their binding affinities were measured fluorimetrically. All the five histones were resolved on SDS page and their binding with DNA was visualized. The values of biding affinities varied with pH and salt concentration. Highest affinity (4.0?×?10⁵ M^?1) was recorded at pH 6.5 in 50 mM phosphate buffer and 1.5?×?10⁴ M^?1 in 2 M NaCl at pH 7.0. The CD spectra support the highest binding affinity with maximum conformational changes at pH 7.0. The time-resolved fluorescence data recorded two life times for histone tyrosine residues at 300 nm emission in phosphate buffer pH 6.5. These life times did not show much change upon binding with DNA in buffer as well as in 2 M NaCl. The isothermal calorimetric studies yielded thermodynamic parameters ΔG, ΔH and ΔS as ?1.6?×?10⁵ cal/mol, ?1.13?×?10³ cal/mol and ?3.80 cal/mol/deg, respectively, evidencing a spontaneous exothermic reaction. The dominant binding forces in building the nucleosome are electrostatic interactions.     

Effect of sequential deletion of extra N-terminal residues on the structure and stability of yeast iso-1-cytochrome-c

A sequence alignment of yeast cytochrome-c (y-cyt-c) with mammalian cyts-c shows that the yeast protein has a five residue long N-terminal extension. A question arises: Does this N-terminal extension play any roles in the stability, structure, and folding of the yeast protein? To answer this question, in silico and in vitro studies were carried out on the wild type (WT) protein and its five deletants (Δ(?5/?5), Δ(?5/?4), Δ(?5/?3), Δ(?5/?2), and Δ(?5/?1) where Δ denotes the deletion and the numbers refer to the residues deleted, e.g. Δ(?5/?1) denotes the deletion of residues numbered from ?5 to ?1 (TEFKA), while Δ(?5/?2) denotes the deletion of resides numbered from ?5 to ?2 (TEFK) and so on). The main conclusion of the in silico study is that the order of stability of deletants and WT protein is Δ(?5/?4) > WT > Δ(?5/?3) > Δ(?5/?5) > Δ(?5/?1) ~ Δ(?5/?2). In vitro studies involved (i) measurements of thermodynamic stability of all proteins by differential scanning calorimetry and from sigmoidal curves of two different structural properties ([θ]₂₂₂, a probe for detecting change in secondary structure, and Δε₄₀₅, a probe for detecting alteration in the heme environment), and (ii) characterization of all proteins by various spectral properties. The main conclusions of the in vitro studies are as follows: (i) The order of thermodynamic stability of all proteins is in excellent agreement with that predicted by in silico studies, and (ii) A sequential deletion of the N-terminal extension has no effects on protein structure and folding.     

Thermodynamics of equilibria of hemoglobins M Milwaukee-I and Saskatoon and isolated chains of hemoglobin a with carbon monoxide

The thermodynamic parameters of the CO-equilibria of isolated chains of hemoglobin A and of two α-chains in hemoglobins M Milwaukee-I and Saskatoon at 25°, pH 7.0 were determined. The parameters for the binding of the first CO molecule to the hemoglobins M were ΔH′=?17 and ?18 kcal/mole heme and ΔS′=?30 and ?29 e.u. for hemoglobins M Milwaukee-I and Saskatoon, respectively. In contrast to this the characteristics of the second step of the binding were ΔH′=+5.9^· and +4.3 kcal/mole and ΔS′=+51 and +49 e.u. These values for the second step were also significantly different from those of the isolated α-chain (ΔH′=?15 kcal/mole and ΔS′=?11 e.u.).     

Application of principal component analysis for the optimisation of lead(II) biosorption

Current study was focused on optimising lead(II) biosorption carried out by living cells of Arthrospira platensis using Principal Component Analysis. Various experimental conditions were considered: initial metal concentration (50 and 100 mg/l), solution pH (4.0, 4.5, 5.0, 5.5) and contact time (10, 20, 30, 40, 50 and 60 min) at constant rotary speed 200 rpm. It was found that when the biomass was separated from experimental solutions by the filtration, almost 50% of initial metal dose was removed by the filter paper. Moreover, pH was the most important parameter influencing examined processes. The Principal Component Analysis indicated that the most optimum conditions for lead(II) biosorption were metal initial concentration 100 mg/l, pH 4.5 and time 60 min. According to the analysis of the first component it might be stated that the lead(II) uptake increases in time. In overall, it was found to be useful for analysing data obtained in biosorption experiments and eliminating insignificant experimental conditions. Experimental data fitted Langmuir and Dubinin–Radushkevich models indicating that physical and chemical absorption take place at the same time. Further studies are necessary to verify how sorption–desorption cycles affect A. platensis cells.     

Removal of Acid Blue25 from aqueous solutions using Bengal gram fruit shell (BGFS) biomass

The feasibility for the removal of Acid Blue25 (AB25) by Bengal gram fruit shell (BGFS), an agricultural by-product, has been investigated as an alternative for high-cost adsorbents. The impact of various experimental parameters such as dose, different dye concentration, solution pH, and temperature on the removal of Acid Blue25 (AB25) has been studied under the batch mode of operation. pH is a significant impact on the sorption of AB25 onto BGFS. The maximum removal of AB25 was achieved at a pH of 2 (83.84%). The optimum dose of biosorbent was selected as 200 mg for the removal of AB25 onto BGFS. Kinetic studies reveal that equilibrium reached within 180 minutes. Biosorption kinetics has been described by Lagergren equation and biosorption isotherms by classical Langmuir and Freundlich models. Equilibrium data were found to fit well with the Langmuir and Freundlich models, and the maximum monolayer biosorption capacity was 29.41 mg g^?1 of AB25 onto BGFS. The kinetic studies indicated that the pseudo-second-order (PSO) model fitted the experimental data well. In addition, thermodynamic parameters have been calculated. The biosorption process was spontaneous and exothermic in nature with negative values of ΔG° (?1.6031 to ?0.1089 kJ mol^?1) and ΔH° (?16.7920 kJ mol^?1). The negative ΔG° indicates the feasibility of physical biosorption process. The results indicate that BGFS could be used as an eco-friendly and cost-effective biosorbent for the removal of AB25 from aqueous solution.     

Biosorption of Heavy Metals (Cd2+, Cu2+, Co2+, and Mn2+) by Thermophilic Bacteria,Geobacillus thermantarcticus and Anoxybacillus amylolyticus: Equilibrium and Kinetic Studies

ABSTRACT

Two strains of thermophilic bacteria, Geobacillus thermantarcticus and Anoxybacillus amylolyticus, were employed to investigate the biosorption of heavy metals including Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ ions. The effects of different biosorption parameters such as pH (2.0–10.0), initial metal concentrations (10.0–300.0 mg L^?1), amount of biomass (0.25–10 g L^?1), temperature (30–80°C), and contact time (15–120 min) were investigated. Concentrations of metal ions were determined by using an inductively coupled plasma optical emission spectrometry (ICP-OES). Optimum pHs for Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ biosorption by Geobacillus thermantarcticus were found to be 4.0, 4.0, 5.0, and 6.0, respectively. For Anoxybacillus amylolyticus, the optimum pHs for Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ biosorption were found to be 5.0, 4.0, 5.0, and 6.0, respectively. The Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ removals at 50 mg L^?1 in 60 min by 50 mg dried cells of Geobacillus thermantarcticus were 85.4%, 46.3%, 43.6%, and 65.1%, respectively, whereas 74.1%, 39.8%, 35.1%, and 36.6%, respectively, for Anoxybacillus amylolyticus. The optimum temperatures for heavy metal biosorption were near the optimum growth temperatures for both strains. Scatchard plot analysis was employed to obtain more compact information about the interaction between metal ions and biosorbents. The plot results were further studied to determine if they fit Langmuir and Freundlich models.     

Influence of pH on Cd and Cu uptake, distribution and their effect on nitrate reductase activity in cucumber (Cucumis sativus L.) seedling roots

Influence of different pH solutions (5.0 and 7.0) on Cu²⁺ and Cd²⁺ absorption and distribution in root cells as well as effects of these metals on nitrate reductase activity (NR) in roots of cucumber seedlings were estimated. The absorption of Cu and Cd by roots measured as metal depletion in uptake solution was similar, both metal absorption was independent of the pH of solution. However, after rinsing of roots in distilled water (30 minutes), more Cu than Cd was found in protoplasts of root cells. More Cu was measured in all cell fractions when Cu was uptaken from pH 5.0 than from 7.0. The nitrate reductase activity after one hour of metal treatments was drastically decreased by Cu. The strongest reduction of enzyme activity was observed in roots treated with Cu in buffer with pH 5.0. Influence of Cd on the enzyme activity was weaker and was independent of the pH of solution. Lower concentration of Cd in solution (20 μM) increased NR activity. The data obtained prove the higher mobility of Cu than Cd into the cells of root. The mobility of Cu depends on pH of solution. Cu ions, but not Cd, influenced membrane permeability (K leakage). Cu acted more drasticly than Cd on NR activity.     

Direct Interaction between Terbium Ion and Peroxidase in Horseradish at Different pH Values

Rare earth elements (REEs) entering plant cells can directly interact with peroxidase in plants, which is the structural basis for the decrease in the activity of peroxidase. Different cellular compartments have different pH values. However, little information is available regarding the direct interaction between REEs and peroxidase in plants at different pH values. Here, we investigated the charge distribution on the surface of horseradish peroxidase (HRP) molecule as well as the interaction of terbium ion (Tb³⁺, one type of REEs) and HRP at different pH values. Using the molecular dynamics simulation, we found that when the pH value was from 4.0 to 8.0, a large amount of negative charges were intensively distributed on the surface of HRP molecule, and thus, we speculated that Tb³⁺ with positive charges might directly interact with HRP at pH 4.0–8.0. Subsequently, using ultraviolet-visible spectroscopy, we demonstrated that Tb³⁺ could directly interact with HRP in the simulated physiological solution at pH 7.0 and did not interact with HRP in other solutions at pH 5.0, pH 6.0 and pH 8.0. In conclusion, we showed that the direct interaction between Tb³⁺ and HRP molecule depended on the pH value of cellular compartments.     

Metal phytoremediation potential of naturally growing plants on fly ash dumpsite of Patratu thermal power station,Jharkhand, India

Three naturally growing plants Ipomoea carnea, Lantana camara, and Solanum surattense were found in fly ash dumpsite of Patratu thermal power station, Jharkhand, India. They were assessed for their metal uptake potential. The fly ash was slightly alkaline with very less nitrogen and organic carbon but enriched with phosphorus and heavy metals. Lantana camara and Ipomoea carnea showed good translocation from root to shoot for most of the metals except Mn and Pb. The order of metal accumulation in stem of both the plants were Fe(205mg/kg)>Mn(65mg/kg)>Cu(22.35mg/kg)>Pb(6.6mg/kg)>Cr(3.05mg/kg)>Ni(1 mg/kg)>Cd(0.5 mg/kg) and Fe(741 mg/kg)>Mn(154.05 mg/kg)>Cu(20.75 mg/kg)>Pb(6.75 mg/kg)>Ni(4.0 mg/kg)>Cr(3.3mg/kg)>Cd(0.05mg/kg), respectively. But Solanum surattense accumulated most of the metals in roots. The order was in the following order, Mn (382.2mg/kg) >Fe (264.1mg/kg) > Cu (25.35mg/kg) >Pb (5.95 mg/kg) > Ni (1.9 mg/kg) > Cr (1.8mg/kg) > Cd (0.55 mg/kg). The order of Bioconcentration factor (BCF) in root and shoot followed almost the same order as, Mn>Fe>Ni>Pb>Cu>Cr≈ Cd in all the three species. ANOVA showed significant variation in metal accumulation by root and stem between the species. Finally, it can be concluded that Solanum surattense can be used as phytostabilizer and other two species as phytoextractor of metal for fly ash dumpsite reclamation.     

The effect of EDTA and EDDS on lead uptake and localization in hydroponically grown Pisum sativum L.

Pisum sativum plants were treated for 3 days with an aqueous solution of 100 μM Pb(NO₃)₂ or with a mixture of lead nitrate and ethylenediaminetetraacetic acid (EDTA) or [S,S]-ethylenediaminedisuccinic acid (EDDS) at equimolar concentrations. Lead decline from the incubation media and its accumulation and localization at the morphological and ultrastructural levels as well as plant growth parameters (root growth, root and shoot dry weight) were estimated after 1 and 3 days of treatment. The tested chelators, especially EDTA, significantly diminished Pb uptake by plants as compared to the lead nitrate-treated material. Simultaneously, EDTA significantly enhanced Pb translocation from roots to shoots. In the presence of both chelates, plant growth parameters remained considerably higher than in the case of uncomplexed Pb. Considerable differences between the tested chelators were visible in Pb localization both at the morphological and ultrastructural level. In Pb+EDTA-treated roots, lead was mainly located in the apical parts, while in Pb+EDDS-exposed material Pb was evenly distributed along the whole root length. Transmission electron microscopy and EDS analysis revealed that in meristematic cells of the roots incubated in Pb+EDTA, large electron-dense lead deposits were located in vacuoles and small granules were rarely noticed in cell walls or cytoplasm, while after Pb+EDDS treatment metal deposits were restricted to the border between plasmalemma and cell wall. Such results imply different ways of transport of those complexed Pb forms.     

Isolation and characterization of iron chelators from turmeric (<Emphasis Type="Italic">Curcuma longa</Emphasis>): selective metal binding by curcuminoids

Iron overload disorders may be treated by chelation therapy. This study describes a novel method for isolating iron chelators from complex mixtures including plant extracts. We demonstrate the one-step isolation of curcuminoids from turmeric, the medicinal food spice derived from Curcuma longa. The method uses iron-nitrilotriacetic acid (NTA)-agarose, to which curcumin binds rapidly, specifically, and reversibly. Curcumin, demethoxycurcumin, and bisdemethoxycurcumin each bound iron-NTA-agarose with comparable affinities and a stoichiometry near 1. Analyses of binding efficiencies and purity demonstrated that curcuminoids comprise the primary iron binding compounds recovered from a crude turmeric extract. Competition of curcuminoid binding to the iron resin was used to characterize the metal binding site on curcumin and to detect iron binding by added chelators. Curcumin-Iron-NTA-agarose binding was inhibited by other metals with relative potency: (>90% inhibition) Cu²⁺ ~ Al³⁺ > Zn²⁺ ≥ Ca²⁺ ~ Mg²⁺ ~ Mn²⁺ (<20% inhibition). Binding was also inhibited by pharmaceutical iron chelators (desferoxamine or EDTA) or by higher concentrations of weak iron chelators (citrate or silibinin). Investigation of the physiological effects of iron binding by curcumin revealed that curcumin uptake by cultured cells was reduced >80% by addition of iron to the media; uptake was completely restored by desferoxamine. Ranking of metals by relative potencies for blocking curcumin uptake agreed with their relative potencies in blocking curcumin binding to iron-NTA-agarose. We conclude that curcumin can selectively bind toxic metals including iron in a physiological setting, and propose inhibition of curcumin binding to iron-NTA-agarose for iron chelator screening.     

Signals of resilience to ocean change: high thermal tolerance of early stage Antarctic sea urchins (Sterechinus neumayeri) reared under present-day and future pCO2 and temperature

We tested the hypothesis that development of the Antarctic urchin Sterechinus neumayeri under future ocean conditions of warming and acidification would incur physiological costs, reducing the tolerance of a secondary stressor. The aim of this study is twofold: (1) quantify current austral spring temperature and pH near sea urchin habitat at Cape Evans in McMurdo Sound, Antarctica and (2) spawn S. neumayeri in the laboratory and raise early developmental stages (EDSs) under ambient (?0.7 °C; 400 µatm pCO₂) and future (+2.6 °C; 650 and 1,000 µatm pCO₂) ocean conditions and expose four EDSs (blastula, gastrula, prism, and 4-arm echinopluteus) to a one hour acute heat stress and assess survivorship. Results of field data from 2011 to 2012 show extremely stable inter-annual pH conditions ranging from 7.99 to 8.08, suggesting that future ocean acidification will drastically alter the pH-seascape for S. neumayeri. In the laboratory, S. neumayeri EDSs appear to be tolerant of temperatures and pCO₂ levels above their current habitat conditions. EDSs survived acute heat exposures >20 °C above habitat temperatures of ?1.9 °C. No pCO₂ effect was observed for EDSs reared at ?0.7 °C. When reared at +2.6 °C, small but significant pCO₂ effects were observed at the blastula and prism stage, suggesting that multiple stressors are more detrimental than single stressors. While surprisingly tolerant overall, blastulae were the most sensitive stage to ocean warming and acidification. We conclude that S. neumayeri may be unexpectedly physiologically tolerant of future ocean conditions.     

The Effect of pH and NaCl Levels on the Physicochemical and Emulsifying Properties of a Cruciferin Protein Isolate

The influence of pH (3.0, 5.0, and 7.0) and ionic strength (0, 50, 100 mM NaCl) on the physicochemical and emulsifying properties of a cruciferin-rich protein isolate (CPI) was investigated. Surface charge on the CPI was found to substantially reduced in the presence of NaCl. Surface hydrophobicity was found to be the lowest for CPI at pH 7.0 with 100 mM NaCl, and highest at pH 3.0 without NaCl. Solubility was found to be lowest at pH 5.0 and 7.0 without NaCl (<20 %), however greatly improved for all other pH and NaCl conditions (>80 %). Interfacial tension was found to be lowest at 10–11 mN/m for pH 5.0–0 mM NaCl and pH 7.0–50/100 mM NaCl, whereas under all other conditions interfacial tension was higher (15+ mN/m). Overall, NaCl has no effect on EAI at pH 3.0 where it ranged between 18.8 and 19.4 m²/g. At pH 5.0, EAI decreased from 21.1 to 12.8 m²/g as NaCl levels increased from 0 to 100 mM. At pH 7.0, EAI values were found to decrease from 14.9 to 5.2 m²/g as NaCl levels were raised from 0 to 100 mM. Overall, ESI was reduced with the addition of NaCl from ~15.7 min at 0 mM NaCl to ~11.6 min and ~12.0 min for the 50 and 100 mM NaCl levels, respectively.     

Role of four conserved aspartic acid residues of EF-loops in the metal ion binding and in the self-assembly of ciliate <Emphasis Type="Italic">Euplotes octocarinatus</Emphasis> centrin

Ciliate Euplotes octocarinatus centrin (EoCen) is an EF-hand calcium-binding protein closely related to the prototypical calcium sensor protein calmodulin. Four mutants (D37K, D73K, D110K and D146K) were created firstly to elucidate the importance of the first aspartic acid residues (Asp37, Asp73, Asp110 and Asp146) in the beginning of the four EF-loops of EoCen. Aromatic-sensitized Tb³⁺ fluorescence indicates that the aspartic acid residues are very important for the metal-binding of EoCen, except for Asp73 (in EF-loop II). Resonance light scattering (RLS) measurements for different metal ions (Ca²⁺ and Tb³⁺) binding proteins suggest that the order of four conserved aspartic acid residues for contributing to the self-assembly of EoCen is Asp37 > Asp146 > Asp110 > Asp73. Cross-linking experiment also exhibits that Asp37 and Asp146 play critical role in the self-assembly of EoCen. Asp37, in site I, which is located in the N-terminal domain, plays the most important role in the metal ion-dependent self-assembly of EoCen, and there is cooperativity between N-terminal and C-terminal domain (especially the site IV). In addition, the dependence of Tb³⁺ induced self-assembly of EoCen and the mutants on various factors, including ionic strength and pH, were characterized using RLS. Finally, 2-p-toluidinylnaphthalene-6-sulfonate (TNS) binding, ionic strength and pH control experiments indicate that in the process of EoCen self-assembly, molecular interactions are mediated by both electrostatic and hydrophobic forces, and the hydrophobic interaction has the important status.     

Comparative acid stress response of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella Typhimurium after habituation at different pH conditions

AIMS: The aim of the study was to evaluate the effect of habituation at different pH conditions on the acid resistance of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica serotype Typhimurium, and to identify potential differences between the adaptive responses of the three pathogens. METHODS: Stationary phase cells of L. monocytogenes, E. coli O157:H7 and S. Typhimurium, grown in glucose-free media, were exposed to pH 3.5 broth directly or after habituation for 90 min at various pH conditions from 4.0 to 6.0. Survivors at pH 3.5 were determined by plating on tryptic soy agar and incubating at 30 degrees C for 48 h. The kinetics (death rate) of the pathogens at pH 3.5 was calculated by fitting the data to an exponential model. RESULTS: Habituation to acidic environments provided protection of the pathogens against lethal acid conditions. This acid protection, however, was found to be pH dependent. For example, for E. coli O157:H7 an increased acid resistance was observed after habituation at a pH range from 4.0 to 5.5, while the maximum acid tolerance was induced at pH 5.0. Furthermore, the effect of low pH habituation was different among pathogens. For L. monocytogenes, E. coli O157:H7 and S. Typhimurium, the pH range within which habituation resulted to increased acid resistance was 5.0-6.0, 4.0-5.5 and 4.0-5.0, respectively, while the maximum acid tolerance was induced after habituation at pH 5.5, 5.0 and 4.5, respectively. SIGNIFICANCE: Acid stress conditions are common within current food processing technologies. The information on adaptive responses of L. monocytogenes, E. coli O157:H7 and S. Typhimurium after habituation to different pH environments provided in the present study, could lead to a more realistic evaluation of food safety concerns and to a better selection of processes in order to avoid adaptation phenomena and to minimize the potential for food safety risks.     

Purification and kinetic characterization of polygalacturonase - 3 from palmyrah palm (Borassus flabellifer L)

Polygalacturonase-3 was isolated and purified to homogeneity from palmyrah palm (Borassus flabellifer L.) fruit using Con A-Sepharose affinity column. The purified enzyme migrated as a single band on native and SDS–polyacrylamide gel electrophoresis. The molecular mass of the purified enzyme was estimated to be 66 kDa by size elution chromatography. Optimum polygalacturonase activity as a function of pH and temperature was determined using polygalacturonic acid as substrate. Optimum pH and temperature values ranged between the pH?4.0–5.0 and temperature 30–40 °C. At the optimum pH and temperature, the K_m and V_max values were determined by Lineweaver–Burk method. The value K_m (0.33 mM) reveals that polygalacturonase has significant reactivity towards polygalacturonic acid. The enzyme showed varied responses towards divalent and monovalent metal ions. Ca²⁺ activated the polygalacturonase-3 enzyme protein. Both teepol and cetyltrimethylammonium bromide inhibited polygalacturonase-3 activity by 44 %, while 2-mercaptoethanol stimulated the enzyme marginally.     

Aluminum effect on starch,soluble sugar,and phytohormone in roots of <Emphasis Type="Italic">Quercus serrata</Emphasis> Thunb. seedlings

Key message

Glucose was a key substance as an energy source in the root growth promotion by Al, and ABA may relate to metabolism involved with its process.

Abstract

Generally, excess aluminum (Al) ions in soil solution are toxic to many cultivated plant species, but beneficial effects of Al for plant growth have been reported. Previously, we reported stimulation of root growth and nitrate reductase (NR) activity by Al. In this study, we focused on sugars, such as sucrose, glucose, and fructose, as energy sources and also signaling substances to regulate root growth. To understand the mechanism of root growth stimulation by Al, we investigated the change in concentration of sugars and phytohormones, and the activity of NR in roots using Quercus serrata seedlings. Ten-week-old Q. serrata seedlings were hydroponically cultured with nutrient solution containing 2.5 mM Al (pH 4.0) or 3.25 mM calcium (Ca) (pH 4.0) for 3 and 15 days. The growth of first lateral root and NR activity was stimulated for 3 and 15 days of Al treatment. The concentration of starch and sucrose decreased, while the concentration of glucose increased in the Al-treated roots. The concentration of abscisic acid (ABA) in Al-treated roots increased gradually throughout the experiment. From the present study, the mechanism of root growth promotion by Al involves a complex signaling network. We suggest that glucose is a key substance as an energy source and a signaling substance to promote root growth induced by Al and ABA may relate to nitrogen (N) and carbon (C) metabolism involved with the signaling network to promote root growth induced by Al.

     

Element content in tissues of spruce seedlings from hydroponic cultures simulating acidification and deacidification

In order to determine the primary causes of coniferous fine root damage and disfunction in acidic soils, hydroponic cultures of young spruce in pH neutral, acidic, and metal ion-amended media were established. After five months, physiological stress in the roots was removed by raising the pH in the acid and metal ion-amended cultures to physiological neutrality. The cellular element analytical techniques of x-ray microprobe (EDXA) and laser-micromass-spectroscopy (LAMMA) were applied to samples of various tissues of the cultured spruce. Nutrient uptake by the fine roots was blocked by the following ions in order of decreasing severity: Al³⁺>H⁺>Fe³⁺>Mn²⁺. Magnesium uptake by the fine root apoplast was greatly inhibited by these blockers as was calcium. Al³⁺ and Fe³⁺ act predominantly in the root cortex, while Mn²⁺ is mobile throughout the whole plant. Besides the roots, nutrient deficiencies are also severe in the shoot bark and needles. Phloem processes might therefore be affected. The ion exchange functions of the fine roots are almost reversed by raising the pH of the solutions; the nutrient cations may then again be taken up by the apoplast and the crown status improved. The consequences of these findings are discussed with regard to soil processes and fertilization (liming) treatments under field conditions     

Phytoremediation Potential and Nutrient Status of Barringtonia acutangula Gaerth. Tree Seedlings Grown Under Different Chromium (CrVI) Treatments

To investigate the effect of different chromium (CrVI) treatments on seedlings of semi-aquatic plant Barringtonia acutangula, hydroponic experiments were conducted. Results revealed that B. acutangula could tolerate much higher CrVI concentration accumulated about 751–2,703 mg kg^?1 dry weight in roots and 50–1,101 mg kg^?1 dry weight in shoots, respectively, under 1.0, 2.0, 3.0, 4.0, and 5.0 mM chromium treatments. CrVI exposure at 1.0–4.0 mM does not exhibit toxicity signs; however, up to 4.0 mM CrVI exposure causes significant decline in growth parameters. Content of macronutrients such as Ca and K decreased under different Cr treatments in roots and shoots, while Mg content of roots and shoots did not influence at the range of 1.0–4.0 mM Cr; however, significant decrease at 5.0 mM Cr, besides P content, significantly shows increasing trends, respectively. Interestingly, sulfur content of roots and shoots show increasing trends at 1.0–2.0 mM Cr; however, severe decrease of up to 3.0–5.0 mM is shown in CrVI treatments. Furthermore, micronutrients content were enhanced under CrVI treatments excluding Cu and Fe since they show significant reduction in shoots as well as in roots. Bioaccumulation factor were also calculated on the basis of results obtained which shows the value of >1 without viewing chromium toxicity symptoms. This study demonstrated that B. acutangula could tolerate CrVI concentrations up to 1.0–4.0 mM Cr which may be useful in chromium phytoremediation programs.