R.D. Tripathi

Chromium (VI) accumulation reduces chlorophyll biosynthesis, nitrate reductase activity and protein content in Nymphaea alba L.

Plants of Nymphaea alba L. grown at various levels of chromium (VI) ranging from 1 to 200 microM accumulated chromium in concentration and duration-dependent manner. At all Cr levels, chromium accumulation by various plant tissues followed the order roots > leaves > rhizomes. Approximately 93% of total chromium present in the medium was accumulated by plants at lowest conentration (1 microM) used in the experiment. Chromium-induced toxicity appears at 1 microM chromium resulting in the build-up of delta-aminolevulinic acid (ALA) and reduced activities of delta-aminolevulinic acid dehydratase (ALAD) and nitrate reductase (NR), total chlorophyll (Chl) and protein contents. Ch1a was more sensitive than Ch1b to chromium toxicity. It could be inferred that chromium toxicity is not located at the level of ALA synthesis, but, probably at the ALAD activity which was more severely affected during chlorophyll biosynthesis. Finally, impaired chlorophyll biosynthesis resulted in reduced total chlorophyll content.

Comparative transcriptome analysis of arsenate and arsenite stresses in rice seedlings

The effect of arsenic (As) exposure on genome-wide expression was examined in rice (Oryza sativa L., ssp. Indica). A group of defense and stress-responsive genes, transporters, heat-shock proteins, metallothioneins, sulfate-metabolizing proteins, and regulatory genes showed differential expression in rice seedlings challenged with arsenate (AsV) and arsenite (AsIII). AsV stress led to upregulation or downregulation of an additional set of genes in comparison to AsIII. Differential expression of several genes that showed the highest contrast in a microarray analysis was validated by following the quantitative changes in the levels of individual transcripts following challenge with AsV, AsIII, Cd, Cr, and Pb. Most of the selected genes responded to challenge by heavy metals such as arsenic. However, expression of one of the cytochrome P450 genes (Os01g43740) in rice root was induced by AsV but not by other heavy metals. Similarly, one glutaredoxin (Os01g26912) is expressed specifically in the AsIII-treated shoot.

Antioxidant defense mechanism in hydroponically grown Zea mays seedlings under moderate lead stress.

The present study was designed to study the process of stress adaptation in roots and shoot of Zea mays seedlings grown under hydroponic conditions during exposure to lead (Pb) (0-200 microM) for 1-7 d. The alterations in growth and in the level of various biochemical parameters were accessed vis-à-vis Pb accumulation. The accumulation of Pb increased in a concentration-duration-dependent manner, however its translocation from root to shoot was low. At the same time, the level of malondialdehyde (MDA) increased with increasing Pb concentration. However, growth parameters, such as dry weight and root length did not show a significant decline to any of the Pb concentrations. In addition, the level of photosynthetic pigments decreased only upon exposure to high Pb concentrations. These results suggested an alleviation of the stress that was presumably being achieved by antioxidants viz., superoxide dismutase (SOD) and catalase (CAT) as well as ascorbic acid (AsA), which increased linearly with increasing Pb levels and exposure time. However, the level of non-protein thiols (NP-SH) in roots, in general, showed a decline beyond 4d that could be attributed to their consumption for the purpose of Pb detoxification. In conclusion, Zea mays can be used as an indicator species for Pb, and the various antioxidants might play a key role in the detoxification of Pb induced toxic effects.

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.

Role of glutathione and phytochelatin in Hydrilla verticillata (l.f.) Royle and Vallisneria spiralis L. under mercury stress

Abstract Both free (Hydrilla verticillata) and rooted (Vallisneria spiralis) submerged plants showed high potential to accumulate mercury, maximum being in roots of V. spiralis. During mercury stress these plants synthesized different species of phytochelatins (PCs), which bind with the accumulated mercury and showed high levels of cysteine and non-protein thiols. The induction of phytochelatins was accompanied by a decline in cellular levels of glutathione in both the plants, although the decline was only observed at high concentration and long duration of Hg in V. spiralis. Buthionine sulfoximine inhibited accumulation of non-protein thiols and glutathione, indicating the involvement of glutathione in phytochelatin synthesis. However, cycloheximide had no effect on early PC synthesis. Results showed that phytochelatins are synthesized in these plants and play a role in mercury detoxification.

Lead induced changes in glutathione and phytochelatin in Hydrilla verticillata (l. f.) Royle

Abstract Effects of lead were studied on cysteine, acid-soluble thiol, glutathione contents and synthesis of phytochelatins (PCs) in a submerged aquatic macrophyte, Hydrilia verticillata grown under cultural conditions. All concentrations of Pb ranging from 0.5–10.0 μM enhanced cysteine content and accumulation of acid-soluble thiols inside plant tissue and synthesis of phytochelatins. Isolated fractions of the Pb-binding complex indicated involvement of phytochelatins in Pb detoxification. The synthesis of these peptides was concomitant with a decline in total glutathione content. Buthionine sulfoximine, an inhibitor of glutathione synthesis, reduced accumulation of acid soluble thiols and total glutathione content. However, the protein synthesis inhibitor cycloheximide did not affect initial accumulation of acid soluble -SH. Results indicated that PC synthesis was induced under lead stress utilizing glutathione as a substrate.

Physico-chemical characteristics and pollution level of Lake Nainital (U.P., India): role of macrophytes and phytoplankton in biomonitoring and phytoremediation of toxic metal ions.

Lake Nainital is the sole source of drinking water for the local people and even to majority of tourists. In background of lake utility and its importance at national level, such study is essential which is focused on toxic metal pollution and current nutrient status of the lake and their magnification by algae and macrophytes. Study has shown that lake water is rich in nutrients which supports growth of many aquatic macrophytes and algal blooms. Besides, water is contaminated with metals like Cr, Cu, Fe, Mn, Ni, Pb and Zn. Concentration of some of them like Fe, Pb and Ni were higher than the recommended maximum permissible limits. Concentration of these metals were also found high in lake sediments. The level of metals amongst various components of lake varied considerably in different season. Plants and algae growing therein accumulated appreciable amount of metals and water roots of Salix being more efficient than others. High metal removing potential of these plants may be significant for biomonitoring studies and could be a useful phytoremediation technology to restore water quality by harvesting submerged and floating biomass inhabiting littoral zone of the lake.

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.

Bioaccumulation of toxic metals (Cr, Cd, Pb and Cu) by seeds of Euryale ferox Salisb. (Makhana) ☆

The level of toxic metals Cr, Cd, Pb and Cu was determined in seeds, water and sediments collected from nine closed waterbodies of Darbhanga, north Bihar, used for cultivation of the edible aquatic macrophyte Euryaleferox Salisb. during harvesting season of the crop for two successive years (1996 and 1997). Seeds bioconcentrated appreciable amount of these toxic metals in the order Pb > Cr > Cu > Cd. The increased load of metal pollution due to domestic and municipal discharges threatened the habitats of the plant. The toxic metal contents in seeds were found positively correlated with the ambient concentration of metals in water and sediments. The importance of these findings has been discussed for national water resource economy of the country and human health perspectives.

Constructed wetland as an ecotechnological tool for pollution treatment for conservation of Ganga river

With aim to develop an efficient and ecofriendly approach for on-site treatment of sewage, a sub-surface flow constructed wetland (CW) has been developed by raising potential aquatic macrophytes; Typha latifolia, Phragmites australis, Colocasia esculenta, Polygonum hydropiper, Alternanthera sessilis and Pistia stratoites in gravel as medium. Sewage treatment potential of CW was evaluated by varying retention time at three different stages of plant growth and stabilization. After 6 months, monitoring of fully established CW indicated reduction of 90%, 65%, 78%, 84%, 76% and 86% of BOD, TSS, TDS, NO3-N, PO4-P and NH4-N, respectively in comparison to inlet after 36 h of retention time. Sewage treatment through CW also resulted in reduction of heavy metal contents. Thus, CW proved an effective method for treatment of wastewater and may be developed along river Ganga stretch as an alternative technology. Treated water may be drained into river to check further deterioration of Ganga water quality.