Cell membrane surface potential (psi0) plays a dominant role in the phytotoxicity of copper and arsenate

Negative charges at cell membrane surfaces (CMS) create a surface electrical potential (psi(0)) that affects ion concentrations at the CMS and consequently affects the phytotoxicity of metallic cations and metalloid anions in different ways. The zeta potentials of root protoplasts of wheat (Triticum aestivum), as affected by the ionic environment of the solution, were measured and compared with the values of psi(0) calculated with a Gouy-Chapman-Stern model. The mechanisms for the effects of cations (H(+), Ca(2+), Mg(2+), Na(+), and K(+)) on the acute toxicity of Cu(2+) and As(V) to wheat were studied in terms of psi(0). The order of effectiveness of the ions in reducing the negativity of psi(0) was H(+) > Ca(2+) approximately Mg(2+) > Na(+) approximately K(+). The calculated values of psi(0) were proportional to the measured zeta potentials (r(2) = 0.93). Increasing Ca(2+) or Mg(2+) activities in bulk-phase media resulted in decreased CMS activities of Cu(2+) ({Cu(2+)}(0)) and increased CMS activities of As(V) ({As(V)}(0)). The 48-h EA50{Cu(2+)}(b) ({Cu(2+)} in bulk-phase media accounting for 50% inhibition of root elongation over 48 h) increased initially and then declined, whereas the 48-h EA50{As(V)}(b) decreased linearly. However, the intrinsic toxicity of Cu(2+) (toxicity expressed in terms of {Cu(2+)}(0)) appeared to be enhanced as psi(0) became less negative and the intrinsic toxicity of As(V) appeared to be reduced. The psi(0) effects, rather than site-specific competitions among ions at the CMS (invoked by the biotic ligand model), may play the dominant role in the phytotoxicities of Cu(2+) and As(V) to wheat.     

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

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

The influence of the ectomycorrhizal fungus Rhizopogon subareolatus on growth and nutrient element localisation in two varieties of Douglas fir (Pseudotsuga menziesii var. menziesii and var. glauca) in response to manganese stress

Acidification of forest ecosystems leads to increased plant availability of the micronutrient manganese (Mn), which is toxic when taken up in excess. To investigate whether ectomycorrhizas protect against excessive Mn by improving plant growth and nutrition or by retention of excess Mn in the hyphal mantle, seedlings of two populations of Douglas fir (Pseudotsuga menziesii), two varieties, one being menziesii (DFM) and the other being glauca (DFG), were inoculated with the ectomycorrhizal fungus Rhizopogon subareolatus in sand cultures. Five months after inoculation, half of the inoculated and non-inoculated seedlings were exposed to excess Mn in the nutrient solution for further 5 months. At the end of this period, plant productivity, nutrient concentrations, Mn uptake and subcellular compartmentalisation were evaluated. Non-inoculated, non-stressed DFM plants produced about 2.5 times more biomass than similarly treated DFG. Excess Mn in the nutrient solution led to high accumulation of Mn in needles and roots but only to marginal loss in biomass. Colonisation with R. subareolatus slightly suppressed DFM growth but strongly reduced that of DFG (-50%) despite positive effects of mycorrhizas on plant phosphorus nutrition. Growth reductions of inoculated Douglas fir seedlings were unexpected since the degree of mycorrhization was not high, i.e. ca. 30% in DFM and 8% in DFG. Accumulation of high Mn was not prevented in inoculated seedlings. The hyphal mantle of mycorrhizal root tips accumulated divalent cations such as Ca, but not Mn, thus not providing a barrier against excessive Mn uptake into the plants associated with R. subareolatus.     

New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(mu-OAc)(mu-OR)2]3+ core: synthesis, characterization and mechanistic studies of H2O2 disproportionation

Two new diMn(III) complexes [Mn(2)(III)L(1)(mu-AcO)(mu-MeO)(methanol)(2)]Br (1) and [Mn(2)(III)L(2)(mu-AcO)(mu-MeO)(methanol)(ClO(4))] (2) (L(1)H(3)=1,5-bis(2-hydroxybenzophenylideneamino)pentan-3-ol; L(2)H(3)=1,5-bis(2-hydroxynaphtylideneamino)pentan-3-ol) were synthesized and structurally characterized. Structural studies evidence that these complexes have a bis(mu-alkoxo)(mu-carboxylato) triply bridged diMn(III) core in the solid state and in solution, with two substitution-labile sites--one on each Mn ion--in cis-position. The two complexes show catalytic activity toward disproportionation of H(2)O(2), with saturation kinetics on [H(2)O(2)], in methanol and dimethyl formamide at 25 degrees C. Spectroscopic monitoring of the H(2)O(2) disproportionation reaction suggests that (i) complexes 1 and 2 dismutate H(2)O(2) by a mechanism involving redox cycling between Mn(2)(III) and Mn(2)(IV), (ii) the complexes retain the dinuclearity during catalysis, (iii) the active form of the catalyst contains bound acetate, and (iv) protons favors the formation of inactive Mn(II) species. Comparison to other dimanganese complexes of the same family shows that the rate of catalase reaction is not critically dependent on the redox potential of the catalyst, that substitution of phenolate by naphtolate in the Schiff base ligand favors formation of the catalyst-substrate adduct, and that, in the non-protic solvent, the bulkier substituent at the imine proton position hampers the binding to the substrate.     

Callose formation as parameter for assessing genotypical plant tolerance of aluminium and manganese

Callose ((1,3)--glucan) formation in plant tissues is induced by excess Al and Mn. In the present study callose was spectrophotometrically quantified in order to evaluate whether it could be used as a parameter to identify genotypical differences in Al and Mn tolerance. Mn leaf-tissue tolerance of cowpea and linseed genotypes was assessed using the technique of isolated leaf tissue floating on Mn solution. Genotypical differences in the density of brown speckles on the leaf tissue (Mn toxicity symptoms) correlated closely with the concentrations of callose for both plant species. In cell suspension cultures Mn excess also induced callose formation. However, differences in tolerance of cowpea genotypes using callose formation as a parameter could only be found in cultured cowpea cells if controls cultured at optimum Mn supply showed low background callose. As soon as after 1 h, Al supply (50 M) induced callose formation predominantly in the 5-mm root tip of soybean seedlings. Callose concentration in the 0–30 mm root tips was inversely related to the root elongation rate when roots were subjected to an increasing Al supply above 10 M. Three soybean genotypes differed in inhibition of root-elongation rate and induction of callose formation when treated with 50 M Al for 8 h. Relative callose concentrations and relative root-elongation rates for these genotypes were significantly negatively correlated.     

Aluminium alleviates manganese toxicity to rice by decreasing root symplastic Mn uptake and reducing availability to shoots of Mn stored in roots

Background and Aims Manganese (Mn) and aluminium (Al) phytotoxicities occur mainly in acid soils. In some plant species, Al alleviates Mn toxicity, but the mechanisms underlying this effect are obscure.Methods Rice (Oryza sativa) seedlings (11 d old) were grown in nutrient solution containing different concentrations of Mn²⁺ and Al³⁺ in short-term (24 h) and long-term (3 weeks) treatments. Measurements were taken of root symplastic sap, root Mn plaques, cell membrane electrical surface potential and Mn activity, root morphology and plant growth.Key Results In the 3-week treatment, addition of Al resulted in increased root and shoot dry weight for plants under toxic levels of Mn. This was associated with decreased Mn concentration in the shoots and increased Mn concentration in the roots. In the 24-h treatment, addition of Al resulted in decreased Mn accumulation in the root symplasts and in the shoots. This was attributed to higher cell membrane surface electrical potential and lower Mn²⁺ activity at the cell membrane surface. The increased Mn accumulation in roots from the 3-week treatment was attributed to the formation of Mn plaques, which were probably related to the Al-induced increase in root aerenchyma.Conclusions The results show that Al alleviated Mn toxicity in rice, and this could be attributed to decreased shoot Mn accumulation resulting from an Al-induced decrease in root symplastic Mn uptake. The decrease in root symplastic Mn uptake resulted from an Al-induced change in cell membrane potential. In addition, Al increased Mn plaques in the roots and changed the binding properties of the cell wall, resulting in accumulation of non-available Mn in roots.     

Characteristic responses of three tropical legumes to the inoculation of two species of VAM fungi in Andosol soils with different fertilities

The growth and mineral nutrition responses were evaluated of three tropical legumes, cowpea (Vigna unguiculata L. cv Kuromame), pigeonpea [Cajanus cajan L. (Millsp.) cv ICPL 86009] and groundnut (Arachis hypogaea cv Nakateyutaka) inoculated with two different species of VAM fungi, Glomus sp. (Glomus etunicatum-like species) and Gigaspora margarita, and grown in Andosols with different fertilities [Bray II-P: topsoil (72 ppm), subsoil (<0.1 ppm)]. Percent fungal root colonization was high in cowpea and groundnut but relatively low in pigeonpea in both soil types. Despite the low rate of root infection, significant growth responses were produced, especially in the inoculated pigeonpea plant. In all legumes, shoot dry matter production was favoured by the inoculations. Increases in shoot biomass due to mycorrhizae were greater in the subsoil than in the topsoil. Mycorrhization raised shoot concentrations of P and Ca (in cowpea and groundnut) and P and K (in pigeonpea) in the topsoil. Whereas the P concentration in shoots in the subsoil was not positively affected by VAM fungi, particularly in cowpea and pigeonpea, the concentration of K in such plants was significantly increased by VAM treatment. The results also showed that mycorrhizal enhancement of shoot micronutrient concentrations was very rare in all plants, with negative effects observed in certain cases. Cu concentration, in particular, was not affected by VAM formation in any of the plants, and Mn and Fe in pigeonpea and groundnut, respectively, remained the same whether plants were mycorrhizal or not. In both soils the three legumes responded to Glomus sp. better than to Gigaspora margarita, and the effects of the VAM fungi on each of the crops relative to the controls were greater in the subsoil than in the topsoil. However, shoot growth of groundnut was not affected as much as cowpea and pigeonpea by the type of soil used. In spite of the relatively low infection of its root, pigeonpea was generally the most responsive of the three legume species in terms of mycorrhizal/nonmycorrhizal ratios.     

A scale of metal ion binding strengths correlating with ionic charge, Pauling electronegativity, toxicity, and other physiological effects

Equilibrium constants for binding to plant plasma membranes have been reported for several metal ions, based upon adsorption studies and zeta-potential measurements. LogK values for the ions are these: Al(3+), 4.30; La(3+), 3.34; Cu(2+), 2.60; Ca(2+) and Mg(2+), 1.48; Na(+) and K(+), 0 M(-1). These values correlate well with logK values for ion binding to many organic and inorganic ligands. LogK values for metal ion binding to 12 ligands were normalized and averaged to produce a scale for the binding of 49 ions. The scale correlates well with the values presented above (R(2)=0.998) and with ion binding to cell walls and other biomass. The scale is closely related to the charge (Z) and Pauling electronegativity (PE) of 48 ions (all but Hg(2+)); R(2)=0.969 for the equation (Scale values)=-1.68+Z(1.22+0.444PE). Minimum rhizotoxicity of metal ions appears to be determined by binding strengths: log a(PM,M)=1.60-2.41exp[0.238(Scale values)] determines the value of ion activities at the plasma membrane surface (a(PM,M)) that will ensure inhibition of root elongation. Additional toxicity appears to be related to softness, accounting for the great toxicity of Ag(+), for example. These binding-strength values correlate with additional physiological effects and are suitable for the computation of cell-surface electrical potentials.     

Toxic effects of Pb2+ on the growth and mineral nutrition of signal grass (Brachiaria decumbens) and Rhodes grass (Chloris gayana)

Although grasses are commonly used to revegetate sites contaminated with lead (Pb), little is known regarding the Pb-tolerance of many of these species. Using dilute solution culture to mimic the soil solution, the growth of signal grass (Brachiaria decumbens Stapf cv. Basilisk) and Rhodes grass (Chloris gayana Kunth cv. Pioneer) was related to the mean activity of Pb²⁺ {Pb²⁺} in solution. There was a 50% reduction in fresh mass of signal grass shoots at 5 μM {Pb²⁺} and at 3 μM {Pb²⁺} for the roots. Rhodes grass was considerably more sensitive to Pb in solution, with shoot and root fresh mass being reduced by 50% at 0.5 μM {Pb²⁺}. The higher tolerance of signal grass to Pb appeared to result from the internal detoxification of Pb, rather than from the exclusion of Pb from the root. At toxic {Pb²⁺}, an interveinal chlorosis developed in the shoots of signal grass (possibly a Pb-induced Mn deficiency), whilst in Rhodes grass, Pb²⁺ caused a bending of the root tips and the formation of a swelling immediately behind some of the root apices. Root hair growth did not appear to be reduced by Pb²⁺ in solution, being prolific at all {Pb²⁺} in both species.     

Manganese toxicity: The significance of magnesium for the sensitivity of wheat plants

The tolerance of wheat to manganese was investigated in soil and solution culture. Although no critical toxicity concentration could be identified, growth was reduced when the ratio of magnesium to manganese in the shoots (R_p) fell below 20:1 (mgg^–1/mgg^–1). In soil, plant growth relative to unstressed plants (Y) could be described by the empirical equation: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeywaiabg2% da9iaaicdacaGGUaGaaGyoaiaaiwdacqGHsislcaaIWaGaaiOlaiaa% iMdacaaI1aGaaeyzaiaabIhacaqGWbGaaiikaiabgkHiTiaaicdaca% GGUaGaaGymaiaaiodacaaI5aGaaeOuamaaBaaaleaacaqGWbaabeaa% kiaacMcaaaa!4959!\[{\text{Y}} = 0.95 - 0.95{\text{exp}}( - 0.139{\text{R}}_{\text{p}} )\]In solution culture the value of R_p was related to the ratio of the two ions in the nutrient solution (R_s) according to the expression: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeysaiaab6% gacaqGGaGaaeOuamaaBaaaleaacaqGWbaabeaakiabg2da9iaaicda% caGGUaGaaGinaiaaikdacqGHRaWkcaaIWaGaaiOlaiaaisdacaaI4a% GaaeiiaiaabMeacaqGUbGaaeiiaiaabkfadaWgaaWcbaGaae4Caaqa% baGccaGGPaaaaa!47B6!\[{\text{In R}}_{\text{p}} = 0.42 + 0.48{\text{ In R}}_{\text{s}}\]The magnesium concentration in the nutrient solution for optimum growth at a given concentration of manganese was given by: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeysaiaab6% gacaqGGaGaae4waiaab2eacaqGNbGaaeyxaiabg2da9iaaikdacaGG% UaGaaGioaiaaiMdacqGHRaWkcaaIWaGaaiOlaiaaiwdacaaI0aGaae% iiaiaabMeacaqGUbGaaeiiaiaabUfacaqGnbGaaeOBaiaab2faaaa!4A0B!\[{\text{In [Mg]}} = 2.89 + 0.54{\text{ In [Mn]}}\]Magnesium increased the tolerance of plants to high concentrations of manganese in shoot tissue and also increased the ability of the plant to discriminate against manganese ions in translocation of nutrients from roots to shoots.     

Distribution and speciation of Mn in hydrated roots of cowpea at levels inhibiting root growth

The phytotoxicity of Mn is important globally due to its increased solubility in acid or waterlogged soils. Short‐term (≤24 h) solution culture studies with 150 µM Mn were conducted to investigate the in situ distribution and speciation of Mn in apical tissues of hydrated roots of cowpea [Vigna unguiculata (L.) Walp. cv. Red Caloona] using synchrotron‐based techniques. Accumulation of Mn was rapid; exposure to 150 µM Mn for only 5 min resulting in substantial Mn accumulation in the root cap and associated mucigel. The highest tissue concentrations of Mn were in the root cap, with linear combination fitting of the data suggesting that ≥80% of this Mn(II) was associated with citrate. Interestingly, although the primary site of Mn toxicity is typically the shoots, concentrations of Mn in the stele of the root were not noticeably higher than in the surrounding cortical tissues in the short‐term (≤24 h). The data provided here from the in situ analyses of hydrated roots exposed to excess Mn are, to our knowledge, the first of this type to be reported for Mn and provide important information regarding plant responses to high Mn in the rooting environment.     

Synthesis,Crystal Structure,and Biological Activities of Two Chiral Mononuclear Mn(III) Complexes

Two new chiral mononuclear Mn^(III) complexes, [Mn L ^{( R )}Cl (C₂H₅OH)]?C₂H₅OH ( 1 ) and [Mn L ^{( S )} (CH₃OH)₂]Cl?CH₃OH ( 2 ), {H₂ L = (R,R)‐or (S,S)‐N,N’‐bis‐(2‐hydroxy‐1‐naphthalidehydene)‐cyclohexanediamine} were synthesized and characterized by various physicochemical techniques. Bond valence sum (BVS) calculations and the Jahn‐Teller effect indicate that the Mn centers are in a +3 oxidation state. The statuses of the two complexes in the solution were confirmed as a pair of enantiomers by electrospray ionization, mass spectrometry (ESI‐MS) spectrum. The binding ability of the complexes with calf thymus CT‐DNA was investigated by spectroscopic and viscosity measurements. Both of the complexes could interact with CT‐DNA via an intercalative mode with the order of 1 ( R ‐enantiomer) > 2 ( S ‐enantiomer). Under the physiological conditions, the two compounds exhibit efficient DNA cleavage activities without any external agent, which also follows the order of R ‐enantiomer > S ‐enantiomer. Interestingly, the concentration‐dependent DNA cleavage experiments indicate an optimal concentration of 17.5 μM. In addition, the interaction of the compounds with bovine serum albumin (BSA) was also investigated, which indicated that the complexes could quench the intrinsic fluorescence of BSA by a static quenching mechanism. Chirality 27:142‐150, 2015. © 2014 Wiley Periodicals, Inc.     

Design, synthesis, and biological evaluation of callophycin A and analogues as potential chemopreventive and anticancer agents

Callophycin A was originally isolated from the red algae Callophycus oppositifolius and shown to mediate anticancer and cytotoxic effects. In our collaborative effort to identify potential chemopreventive and anticancer agents with enhanced potency and selectivity, we employed a tetrahydro-β-carboline-based template inspired by callophycin A for production of a chemical library. Utilizing a parallel synthetic approach, 50 various functionalized tetrahydro-β-carboline derivatives were prepared and assessed for activities related to cancer chemoprevention and cancer treatment: induction of quinone reductase 1 (QR1) and inhibition of aromatase, nitric oxide (NO) production, tumor necrosis factor (TNF)-α-induced NFκB activity, and MCF7 breast cancer cell proliferation. Biological results showed that the n-pentyl urea S-isomer 6a was the strongest inducer of QR1 with an induction ratio (IR) value of 4.9 at 50 μM [the concentration to double the activity (CD)=3.8 μM] and its corresponding R-isomer 6f had an IR value of 4.3 (CD=0.2 μM). The isobutyl carbamate derivative 3d with R stereochemistry demonstrated the most potent inhibitory activity of NFκB, with the half maximal inhibitory concentration (IC(50)) value of 4.8 μM, and also showed over 60% inhibition at 50 μM of NO production (IC(50)=2.8 μM). The R-isomer urea derivative 6j, having an appended adamantyl group, exhibited the most potent MCF7 cell proliferation inhibitory activity (IC(50)=14.7 μM). The S-isomer 12a of callophycin A showed the most potent activity in aromatase inhibition (IC(50)=10.5 μM).     

Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear Mn2(II,III) complex

Simulation of X- and Q-band electron paramagnetic resonance (EPR) spectra of an unsymmetric dinuclear [Mn(2)(II,III)L(mu-OAc)(2)]ClO(4) complex (1), (L is the dianion of 2-{[N,N-bis(2-pyridylmethyl)amino]methyl}-6-{[N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N-(2-pyridylmethyl)amino]methyl}-4-methylphenol) was performed using one consistent set of simulation parameters. Rhombic g-tensors and hyperfine tensors were necessary to obtain satisfactory simulation of the EPR spectra. The anisotropy of the effective hyperfine tensors of each individual (55)Mn ion was further analyzed in terms of intrinsic hyperfine tensors. Detailed analysis shows that the hyperfine anisotropy of the Mn(III) ion is a result of the Jahn-Teller effect and thus an inherent character. In contrast, the anomalous hyperfine anisotropy of the Mn(II) ion is attributed as being transferred from the Mn(III) ion through the spin exchange interaction. The anisotropy parameter for the Mn(II) is deduced as D(II)=-1.26+/-0.2cm(-1). This is the first reported D(II) value for a Mn(II) ion in a weakly exchange coupled mixed-valence Mn(2)(II,III) complex with a bis-mu-acetato-bridge. The [see text] electronic configuration of the Mn(III) ion in 1 is revealed by the negative sign of its intrinsic hyperfine tensor anisotropy, Deltaa(III)=a(z)-a(x,y)=-46cm(-1). Lower spectral resolution of the Q-band EPR spectrum as compared to the X-band EPR spectrum is associated to large line width broadening of the x- and y-components in contrast to the z-component. The origins of the unequal distribution of line width between the z- and x-, y-components are discussed.     

Synthesis, structure and interactions with DNA of novel tetranuclear, [Mn4(II/II/II/IV)] mixed valence complexes

Reaction of Mn(II) with phenoxyalkanoic acids and di-2-pyridyl ketone oxime (Hpko) leads to neutral tetranuclear complexes of the general formula Mn(4)(O)(pko)(4)(phenoxyalkanoato)(4) (phenoxyalkanoic acids: H-mcpa=2-methyl-4-chloro-phenoxy-acetic acid, H-2,4,5-T=2,4,5-trichloro-phenoxy-acetic acid or H3,4-D=3,4-dichloro-phenoxy-acetic acid). The compounds were synthesized by adding di-2-pyridyl ketone oxime to MnCl(2) in the presence of the sodium salts of the alkanoic acids in methanol. The crystal structure of Mn(4)(II/II/II/IV)(O)(pko)(4)(2,4,5-T)(4).2.5CH(3)OH.0.25H(2)O 1 shows that the complex consists of a [Mn(4)(mu(4)-O)](8+) core with a Mn(IV) and 3 Mn(II) ions in octahedral environment and a mu(4)-O atom bridging the four manganese ions. Spectroscopic studies of the interaction of these tetranuclear clusters with DNA showed that these compounds bind to dsDNA. The binding strength of the Mn(4)(II/II/II/IV)(O)(pko)(4)(2,4,5-T)(4) complex for calf thymus DNA is equal to 1.1x10(4)M(-1). Among the deoxyribonucleotides they bind preferentially to deoxyguanylic acid (dGMP). Competitive studies with ethidium bromide (EthBr) showed that the Mn(4)(II/II/II/IV)(O)(pko)(4)(2,4,5-T)(4) complex exhibited the ability to displace the DNA-bound EthBr indicating that the complex binds to DNA via intercalation in strong competition with EthBr for the intercalative binding site. Additionally, DNA electrophoretic mobility experiments showed that all three complexes, at low cluster concentration, are obviously capable of binding to pDNA causing its cleavage (relaxation) at physiological pH and temperature. At higher cluster concentration, catenated dimer forms of pDNA was formed.     

Aspects of the Fe and Mn nutrition of rice plants

Summary In three water-culture experiments, the effects of variations in pH, N form, and Si- and P level on the uptake and translocation of Fe and Mn, and on the chlorophyll contents of lowland rice were examined.It was found that Mn uptake increased with increasing pH, that it was not affected by variations in N form (NO₃ or NH₄), and that Si has a suppressive effect on Mn uptake. With increasing pH, the translocation of Fe to the shoots was reduced. This pH effect might be indirect, in that Fe translocation is hampered by excessive Mn uptake induced by high pH. Variations in N form and in Si level did not influence Fe uptake and- translocation.A combination of high P-and high Mn levels in solution proved to reduce the translocation of Fe to the rice shoots. Precipitation of Mn phosphate on the roots is likely to occur at high concentrations of both Mn and P in the root medium.A negative correlation was found between chlorophyll content and Mn content of the leaves. The chlorophyll content was not related to the iron content of the leaves. It is likely that chlorosis of rice leaves in an early growth stage can be caused by several combinations of the following factors: 1. high Mn supply, 2. NO₃ nutrition inducing an increase in solution pH favouring a further increase in Mn uptake, 3. absence of Si which exerts a suppressive effect on Mn uptake, and 4. high P supply. These factors can induce chlorosis, with and without exerting a concomitant influence on the uptake and translocation of Fe.     

Determination of the degree of acetylation of chitosan by UV spectrophotometry using dual standards

Determination of the degree of acetylation of chitosan by UV spectrophotometry using dual standards is investigated. The UV absorbance of a pure chitosan solution is contributed additively by the N-acetylglucosamine and glucosamine residues; the absorbance divided by the total molar concentration of the residues (A/c(t)) is linearly related to the degree of acetylation (DA). Using acetyl glucosamine and glucosamine hydrochloride as standards in 0.1M hydrochloric acid solution, the equation obtained by linear regression is A/c(t)=3.3615 DA+0.0218, R(2)=0.9958. The DA of the analytical sample (m milligram of chitosan in V liters solution) can be calculated by.     

Temporal and positional relationships between Mn uptake and low-pH-induced root hair formation in Lactuca sativa cv. Grand Rapids seedlings

We investigated whether low-pH-induced manganese (Mn) deficiency causes low-pH-induced root hair formation in lettuce seedlings. Both the number and length of root hairs increased in 0 μM Mn (Mn-free) at pH 6 and decreased in 3 mM Mn (excess Mn) at pH 4 compared with the values in 10 μM Mn (normal Mn). These results indicate an inhibitory effect of Mn on both root hair initiation and elongation. The time dependency of root hair induction caused by Mn deficiency corresponded to that caused by low pH. Within 1 h after the pH of the culture medium was reduced from pH 6 to pH 4, the Mn uptake by roots decreased to 43% of that at pH 6. These results suggest that low-pH-induced Mn deficiency promotes root hair formation. At low pH, the rate of Mn uptake was reduced in areas >2 mm from the root tip. Roots with low-pH-induced root hairs still showed low Mn uptake during 3 h of incubation at pH 6. Therefore, the additional root hairs induced by low pH did not compensate for the low-pH-induced decrease in Mn uptake     

Callose deposition in leaves of cowpea (Vigna unguiculata [L.] Walp.) as a sensitive response to high Mn supply

First macroscopic visible symptoms of Mn toxicity in cowpea (Vegna unguiculata [L.] Walp.) plants grown in solution culture were dark brown spots on the older leaves. Close to these spots, large quantities of substances which fluorescence with aniline blue were deposited, indicating formation of (1,3)-β-glucan (callose). Callose formation in the leaf epidermis was a more sensitive indicator of Mn toxicity than the appearance of macroscopic symptoms, or the Mn concentration in the leaf.