silicon and arsenic-acid

Arsenic (As) is the most hazardous soil contaminant, which inactivates metabolic enzymes and restrains plant growth. To withstand As stress conditions, use of some alleviative tools, such as arbuscular mycorrhizal (AM) fungi and silicon (Si), has gained importance. Therefore, the present study evaluated comparative and interactive effects of Si and arbuscular mycorrhiza-Rhizophagus irregularis on phytotoxicity of arsenate (As V) and arsenite (As III) on plant growth, ROS generation, and antioxidant defense responses in pigeonpea genotypes (Tolerant-Pusa 2002; Sensitive-Pusa 991). Roots of As III treated plants accumulated significantly higher total As than As V supplemented plants, more in Pusa 991 than Pusa 2002, which corresponded to proportionately decreased plant growth, root to biomass ratio, and oxidative burst. Although Si nutrition and AM inoculations improved plant growth by significantly reducing As uptake and the resultant oxidative burst, AM was relatively more efficient in upregulating enzymatic and non-enzymatic antioxidant defense responses as well as ascorbate-glutathione pathway when compared with Si. Pusa 2002 was more receptive to Si nourishment due to its ability to establish more efficient mycorrhizal symbiosis, which led to higher Si uptake and lower As concentrations. Moreover, +Si+AM bestowed better metalloid resistance by further reducing ROS and strengthening antioxidants. Results demonstrated that the genotype with more efficient AM symbiosis in As-contaminated soils could accrue higher benefits of Si fertilization in terms of metalloid tolerance in pigeonpea.

Topics: Antioxidants; Arsenates; Arsenic; Arsenites; Ascorbic Acid; Biomass; Cajanus; Genotype; Glomeromycota; Glutathione; Mycorrhizae; Plant Development; Plant Roots; Silicon; Soil Pollutants; Symbiosis; Vanadium

Silicon (Si) may decrease the uptake and accumulation of arsenic (As) in rice. However, the effects of Si/As ratios in growth medium on arsenic uptake, arsenite efflux to the external medium and translocation of arsenite in rice are currently unclear. Rice seedlings (Oryza sativa L.) were exposed to nutrient solutions with 10 μM arsenite [As(III)] or 10 μM arsenate [As(V)] to explore the influence of different silicic acid concentrations (0, 10, 100, 1000 μM) on arsenic uptake and translocation of arsenite with or without 91 μM phosphate for 24 h. Arsenic speciation was determined in nutrient solutions, roots, and shoots. In the arsenite treatments, different Si/As ratios (1:1, 10:1, 100:1) did not affect As(III) uptake by rice roots, however they did inhibit translocation of As(III) from roots to shoots significantly (P < 0.001) in the absence of P. In the arsenate treatments, a Si/As ratio of 100:1 significantly decreased As(V) uptake and As(III) efflux compared with the control (Si/As at 0:1), accounting for decreases of 27.4% and 15.1% for -P treatment and 47.8% and 61.1% for + P treatment, respectively. As(III) is the predominant species of arsenic in rice roots and shoots. A Si/As ratio of 100:1 reduced As(III) translocation from roots to shoots markedly without phosphate. When phosphate was supplied, As(III) translocation from roots to shoots was significantly inhibited by Si/As ratios of 10:1 and 100:1. The results indicated that in the presence of P, different silicic acid concentrations did not impact arsenite uptake and transport in rice when arsenite was supplied. However, a Si/As ratio of 100:1 inhibited As(V) uptake, as well as As(III) efflux and translocation from roots to shoots when arsenate was supplied.

Topics: Arsenates; Arsenic; Arsenites; Oryza; Plant Roots; Seedlings; Silicon; Soil Pollutants

A series of spiro-arsoranes bearing a phenyl moiety as the fifth substituent were synthesized applying open-chain, as well as cyclic vicinal diols, as chelating molecules by condensation reactions in aprotic solvents. The products synthesized are the spiro compounds of the general formula PhAs(DiolH(-2))(2) derived from the vicinal diols meso-2,3-butanediol, PhAs(meso-2,3-ButdH(-2))(2) (1), exo-cis-2,3-norbornanediol, PhAs{exo-cis-NobdH(-2)}(2) (2), cis-1,2-cyclopentanediol, PhAs(cis-1,2-CptdH(-2))(2) (3), anhydroerythritol, PhAs(AnErytH(-2))(2) (4), cis-1,2-cyclohexanediol, PhAs(cis-1,2-ChxdH(-2))(2) (5), and rac-trans-1,2-cyclohexanediol, rac-{PhAs(trans-1,2-ChxdH(-2))(2)} (6) which were identified as mononuclear compounds. A novel dimeric double-spiro environment for oxyarsoranes was found in the reaction products derived from the sterically demanding diols 1,1'-bicyclohexyl-1,1'-diol {PhAs(BhxdH(-2))O}(2) (7) and perfluorpinacol, {PhAs(FpinH(-2))O}(2) (8). The stability of the compounds in acidic and neutral aqueous media in the presence of organic co-solvents was investigated. A convenient synthetic procedure for spiro-oxyarsoranes, applying water as the solvent, was developed and proven to be advantageous. All of the compounds synthesized in this study were characterized by means of melting-point measurement, single-crystal X-ray analysis, NMR, IR, Raman, UV/vis, and mass spectrometry. The principles found for these reactions were valid for the methyl glycosides of beta-D-ribofuranose and alpha-D-mannopyranose. The spiro-arsorane derived from methyl alpha-D-mannopyranoside, PhAs(Me-alpha-D-Manp2,3H(-2))(2) (9), is the first example of a structurally characterized carbohydrate-arsenic(V) compound.

Topics: Alkylation; Arsenates; Arsenicals; Carbohydrates; Chelating Agents; Crystallography, X-Ray; Hydrolysis; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Structure; Silicon