Silicon-mediated genotoxic alterations in Brassica juncea under arsenic stress: A comparative study of biochemical and molecular markers

Arsenic (As), one of the most harmful toxicant at the global level, severely affects plant metabolism when taken up. Interestingly, the presence of silicon (Si) as a fertilizer in As-contaminated soil is an effective strategy to decrease As accumulation in plants. Brassica juncea (var. Varuna) were grown hydroponically to investigate the role of Si at biochemical and molecular levels under arsenite (As³⁺) stress. Seedlings of B. juncea were exposed to As³⁺, Si, and a combination of both elements. Our data demonstrated that seedlings exposed to As³⁺ showed an inhibition in shoot length, chlorophyll, carotenoid, and protein, while co-application of Si improved these growth parameters. Silicon supplementation reduced As accumulation in shoot. Increase/decrease was observed in stress-related parameters (cysteine and proline), antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, and catalase), and oxidative stress markers (malondialdehyde and H₂O₂), which were improved upon co-application of Si as compared to As³⁺ alone treatment. Random amplified polymorphic DNA (RAPD) is a suitable biomarker assay for plants for assessing the genotoxicity. Seven RAPD primers produced a total of 39 and 48 bands in the leaves of the untreated and treated seedlings, respectively. The RAPD band-profiles and genomic template stability were consistent with other growth and physiological parameters. In conclusion, the genotoxic alterations along with the biochemical parameters indicate that the exposure to Si mitigates As³⁺-induced oxidative stress by improving the stress-related parameters and antioxidant system in B. juncea.     

Selenium enriched Garden gress (<Emphasis Type="Italic">Lepidium sativum</Emphasis> L.): Role of antioxidants and stress markers

Selenium (Se) is considered as an essential micronutrient for humans and animals. Sprouts of Garden cress (Lepidium sativum) were treated with different concentration of Se, growth parameters, antioxidant enzymes and stress markers were studied. 10 μM Se would be more beneficial, as at this concentration it showed altered biochemical traits without showing any toxicity symptoms.     

Cadmium Regulated Nitrate Reductase Activity in Hydrilla Verticillata (1.f.) Royle

The study was conducted to evaluate the suitability of nitrate reductase activity and the level of some metabolites as an in vivo test system for cadmium toxicity in submerged macrophyte Hydrilla verticillata. Cadmium (Cd) concentrations ranging from 0.01-80 μM affected nitrate reductase activity in a differential way. It had stimulatory effect up to 1.0 μM Cd, while higher concentrations inhibited the enzyme activity significantly. The protein synthesis inhibitor cycloheximide inhibited Cd-stimulated nitrate reductase activity during in vivo and in vitro assays. However, the effect of Cd on NR activity under in vitro assay was more pronounced. Although low Cd exposures had no effect, higher metal exposures augmented nitrate uptake. This Cd-induced NO₃ ^- uptake did not result in recovery of inhibited enzyme activity in vivo. It appears that nitrate reductase activity is more sensitive to Cd toxicity than the eventual products of nitrate assimilation such as total organic nitrogen and soluble proteins. There was a differential response of chlorophyll levels to Cd; lower concentrations enhanced the pigment level while higher ones reduced it. Cadmium exposure always enhanced the levels of carotenoids. Results showed that nitrate reductase activity could serve as an useful bioassay for Cd contamination using H. verticillata.     

A Study on Fluoride Sorption by Montmorillonite and Kaolinite

Fluoride (F) sorption by acidified montmorillonite, montmorillonite and kaolinite has been investigated as a function of period of agitation, pH, initial fluoride concentration and clay amount. In case of montmorillonite and kaolinite, F sorption is insignificant at pH > 7, while it is maximum at pH 4. Enhanced F sorption by acidified montmorillonite is noted at pH < 10, maximum being at pH 6. Significant concentration of Al³⁺,Fe³⁺ and silica are released from acidified montmorillonite lattice (pH ≈ 2; 1:10 w/v), which decreased considerably owing to the formation of hydroxy (Al and Fe) silicates on subsequent base addition. Soluble fluoro-complexes at pH ≈ 2 and chemical interaction of F with hydroxy (Al and Fe) silicates at pH > 4, are potent sink for F in case of acidified montmorillonite. Soluble fluoro-complexes are also detected in case of montmorillonite and kaolinite at pH ≈ 4. Saturation indices (SIs) for acidified montmorillonite, over the studied pH range (2–10) has also been computed.