Seema Mishra

Effect of arsenic on growth, oxidative stress, and antioxidant system in rice seedlings ☆

The physiological, biochemical, and proteomic changes in germinating rice seedlings were investigated under arsenic stress. A marked decrease in germination percentage, shoot, and root elongation as well as plant biomass was observed with arsenic treatments, as compared to control, whereas accumulation of arsenic and malondialdehyde (MDA) in seedlings were increased significantly with increasing arsenic concentration (both AsIII and AsV). The up-regulation of some antioxidant enzyme activities and the isozymes of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), peroxidase (POD, EC 1.11.1.7), and glutathione reductase (GR, 1.6.4.2) substantiated that arsenic accumulation generated oxidative stress, which was more pronounced in As(III) treatment. We also studied the protective effect of reduced glutathione (GSH) and cysteine (Cys) to As(III)/As(V) stressed seedlings. Both GSH and Cys imparted enhanced tolerance to seedlings against arsenic stress. Seedlings growth improved while level of MDA declined significantly when GSH and Cys were supplemented to As(III)/As(V) treatments suggesting GSH and Cys-mediated protection against oxidative stress. The arsenic content was highest in roots of seedlings grown in As(III) in the presence of GSH/Cys. However, in case of As(V) plus GSH or Cys, the arsenic content in seedlings was highest in shoots. The results are suggestive of differential metabolism of As(III) and As(V) in rice.

Thiol metabolism play significant role during cadmium detoxification by Ceratophyllum demersum L.

In the present study, the level of thiols and activity of related enzymes were investigated in coontail (Ceratophyllum demersum L.) plants to analyze their role in combating the stress caused upon exposure to cadmium (Cd; 0-10 microM) for a duration up to 7d. Plants showed the maximum accumulation of 1293 microg Cd g(-1)dw after 7d at 10 microM. Significant increases in the level of total non-protein thiols (NP-SH) including phytochelatins (PCs) as well as upstream metabolites of the PC biosynthetic pathway, cysteine and glutathione (GSH) were observed. In addition, significant increases in the activities of cysteine synthase (CS), glutathione-S-transferase (GST), glutathione reductase (GR), as well as in vitro activation of phytochelatin synthase (PCS), were noticed in response to Cd. In conclusion, under Cd stress, plants adapted to a new metabolic equilibrium of thiols through coordinated synthesis and consumption to combat Cd toxicity and to accumulate it.

Arsenate Exposure Affects Amino Acids, Mineral Nutrient Status and Antioxidants in Rice (Oryza sativa L.) Genotypes

Simulated pot experiments were conducted on four rice (Oryza sativa L.) genotypes (Triguna, IR-36, PNR-519, and IET-4786) to examine the effects of As(V) on amino acids and mineral nutrient status in grain along with antioxidant response to arsenic exposure. Rice genotypes responded differentially to As(V) exposure in terms of amino acids and antioxidant profiles. Total amino acid content in grains of all rice genotypes was positively correlated with arsenic accumulation. While, most of the essential amino acids increased in all cultivars except IR-36, glutamic acid and glycine increased in IET-4786 and PNR-519. The level of nonprotein thiols (NPTs) and the activities of superoxide dismutase (SOD; EC 1.15.1.1), glutathione reductase (GR; EC 1.6.4.2) and ascorbate peroxidase (APX; EC 1.11.1.11) increased in all rice cultivars except IET-4786. A significant genotypic variation was also observed in specific arsenic uptake (SAU; mg kg(-1)dw), which was in the order of Triguna (134) > IR-36 (71) > PNR-519 (53) > IET-4786 (29). Further, application of As(V) at lower doses (4 and 8 mg L(-1) As) enhanced the accumulation of selenium (Se) and other nutrients (Fe, P, Zn, and S), however, higher dose (12 mg L(-1) As) limits the nutrient uptake in rice. In conclusion, low As accumulating genotype, IET-4786, which also had significantly induced level of essential amino acids, seems suitable for cultivation in moderately As contaminated soil and would be safe for human consumption.

Phytoremediation efficiency of Portulaca tuberosa rox and Portulaca oleracea L. naturally growing in an industrial effluent irrigated area in Vadodra, Gujrat, India

Phytoremediation is a novel, solar-driven and cost-effective technology for the remediation of heavy metal contaminated environments through exploitation of plants ability to accumulate heavy metals in their harvestable shoot parts. In the present investigation, we collected plants of two species of Portulaca i.e. P. tuberosa and P. oleracea from field sites in Vadodra, Gujrat, India. At one site, field was being irrigated with industrial effluent while at other with tube well water. Analysis of heavy metals was performed in industrial effluent, tube well water, soils irrigated with them, and in different parts viz., roots, stem, leaves and flowers of the plant samples. Industrial effluent and soil irrigated with it had very high level of heavy metals (Fe, Zn, Cd, Cr and As) as compared to the tube well water and soil irrigated with that. Plants of both the species growing in effluent irrigated soils showed high accumulation of metals in all plant parts with the maximum being in roots and the least in flowers. Interestingly, both species of Portulaca hyperaccumulated more than one heavy metal viz., Cd, Cr and As. The total shoot concentrations (μg g−1 dw) of Cd, Cr and As in P. tuberosa were 1,571, 7,957 and 3,118, respectively while in P. oleracea, these were 1,128, 7,552 and 2,476, respectively. Portulaca plants have good biomass and high regeneration potential; hence appear to be suitable for the remediation of effluent (metal) contaminated areas.

Response of antioxidant enzymes in coontail (Ceratophyllum demersum L.) plants under cadmium stress

Cadmium (Cd) contamination of aquatic systems is of major concern since it is a nonessential element and hampers plant growth upon accumulation. The aim of this study was to investigate the Cd accumulation behavior of coontail plant, Ceratophyllum demersum L., toxicity induced and response of the antioxidant system. Plants were exposed to various concentrations of Cd (0–10 μM) for a period of 1–7 days. Accumulation of Cd was found to be a concentration duration dependent phenomenon. The maximum accumulation of Cd, 1293 μg g−1 dw, was observed after 7 days at 10 μM. Plants showed significant stimulation of the activities of various antioxidant enzymes viz., superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), guaiacol peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), and glutathione reductase (EC 1.6.4.2) and tolerated toxicity of Cd up to moderate concentration of 5 μM. At 10 μM exposure, enzyme activities declined and plants experienced toxicity, which was evident by the significant decrease in the photosynthetic pigments and by increase in the levels of H2O2, lipid peroxidation and ion leakage. In conclusion, modulation of antioxidant system in a coordinated manner in response to Cd accumulation appears to help plants tolerate toxicity of Cd up to 5 μM.

Characterization of native microalgal strains for their chromium bioaccumulation potential: Phytoplankton response in polluted habitats

Due to its various uses, Cr contamination has become widespread in a diverse array of environments. The present study was carried out during 2007-2008 to investigate the accumulation potential of metals (Cr, Cu, Fe, Mn, Ni and Zn) and metalloid (As) by green (GA) and blue green (BGA) microalgae growing naturally in selected Cr-contaminated sites in districts Unnao and Kanpur (Uttar Pradesh, India). This investigation is a preliminary work to identify suitable native microalgae for biomonitoring and phytoremediation purposes. A total of 22 GA and 11 BGA were encountered in three seasons (summer, rainy and winter). Among these, the accumulation potential was evaluated in high biomass producing strains of BGA (three) and GA (nine). The maximum accumulation of Cr was shown by Phormedium bohneri (8550 microg g(-1)dw) followed by Oscillatoria tenuis (7354 microg g(-1)dw), Chlamydomonas angulosa (5325 microg g(-1)dw), Ulothrix tenuissima (4564 microg g(-1)dw), and Oscillatoria nigra (1862 microg g(-1)dw); all of which demonstrated a transfer factor of >10% for Cr. The results also indicate that the phytoplankton diversity was modified by Cr pollution. BGA represented the dominant community where Cr concentration was higher (11.84 and 2.27 mg L(-1)) (r=0.695), whereas GA showed negative correlation with respect to Cr concentration (r=-0.567). In conclusion, different algal species were able to grow in Cr-contaminated sites and to accumulate significant amounts of Cr with a high transfer factor.

Effect of lead on growth and nitrate assimilation of Vigna radiata (L.) Wilczek seedlings in a salt affected environment

The inhibition of seedling growth and nitrate reductase activity in 5 d old Vigna radiata (L.) Wilczek cv. Pusa Baisakhi in the presence of 1.0 mM lead acetate increased drastically, if NaCl (6 and 12 EC) was also present in the nutrient media along with the metal salt. Correspondingly higher endogenous Na+ levels were accumulated in the roots and leaves of seedlings in presence of the two stresses. On the other hand, the levels of endogenous lead get reduced in presence of NaCl in both the roots and leaves. Roots accumulated more Pb2+ and Na+ than the leaves. The two stresses affect more drastically in the additive or even synergistic manner during the early growth phase of the seedlings.

Screening of native plants and algae growing on fly-ash affected areas near National Thermal Power Corporation, Tanda, Uttar Pradesh, India for accumulation of toxic heavy metals

The present investigation was carried out to screen native plants growing in fly-ash (FA) contaminated areas near National Thermal Power Corporation, Tanda, Uttar Pradesh, India with a view to using them for the eco-restoration of the area. A total number of 17 plants (9 aquatic, 6 terrestrial and 2 algal species) were collected and screened for heavy metal (Fe, Zn, Cu, Mo, B, Si, Al, Cr, Pb, Cd, Hg and As) accumulation. Differential accumulation of various heavy metals by different species of plants was observed. Hydrilla verticillata was found to be the most efficient metal accumulator among 9 aquatic plants, Eclipta alba among 6 terrestrial plants and Phormedium papyraceum between 2 algal species. In general, the maximum levels of most metals were found in terrestrial plants while the lowest in algal species. However, translocation of the metals from root to shoot was found to be higher in aquatic plants than terrestrial ones. These results suggest that various aquatic, terrestrial and algal species of plants may be used in a synergistic way to remediate and restore the FA contaminated areas.

Nitric Oxide Alleviated Arsenic Toxicity by Modulation of Antioxidants and Thiol Metabolism in Rice (Oryza sativa L.)

Nitric oxide (NO) is a gaseous signaling molecule and has a profound impact on plant growth and development. It is reported to serve as pro oxidant as well as antioxidant in plant system. In the present study, we evaluated the protective role of NO against arsenate (AsV) toxicity in rice plants. AsV exposure has hampered the plant growth, reduced the chlorophyll content, and enhanced the oxidative stress, while the exogenous NO supplementation has reverted these symptoms. NO supplementation has reduced the arsenic (As) accumulation in root as well as shoot. NO supplementation to AsV exposed plants has reduced the gene expression level of OsLsi1 and OsLsi2. AsV stress significantly impacted thiol metabolism, it reduced GSH content and GSH/GSSG ratio, and enhanced the level of PCs. NO supplementation maintained the GSH/GSSG ratio and reduced the level of PCs. NO supplementation reverted AsV induced iron deficiency in shoot and had significant impact of gene expression level of various iron transporters (OsYSL2, OsFRDL1, OsIRT1, and OsIRO2). Conclusively, exogenous application of NO could be advantageous against AsV toxicity and could confer the tolerance to AsV stress in rice.

Analysis of sublethal arsenic toxicity to Ceratophyllum demersum: subcellular distribution of arsenic and inhibition of chlorophyll biosynthesis

Highlight At sublethal toxic concentrations, arsenic is predominantly localized in the nucleus but is already able to inhibit chlorophyll biosynthesis upstream of coproporphyrinogen III.