Stanislaus F. D’Souza

Identification and profiling of arsenic stress-induced microRNAs in Brassica juncea

MicroRNAs (miRNAs) constitute a novel mechanism of gene regulation affecting plant development, growth, and stress response. To study the role of miRNAs in arsenic (As) stress, microarray profiling of miRNAs was performed in Brassica juncea using a custom Phalanx Plant OneArray containing 381 unique miRNA probes representing 618 miRNAs from 22 plant species. miRNA microarray hybridization of roots exposed to As for 1h and 4h revealed that a total of 69 miRNAs belonging to 18 plant miRNA families had significantly altered expression. The As-responsive miRNAs also exhibited a time- and organ-dependent change in their expression. Putative target prediction for the miRNAs suggested that they regulate various developmental processes (e.g. miR156, miR169, and miR172), sulphur uptake, transport, and assimilation (miR395, miR838, and miR854), and hormonal biosynthesis and/or function (e.g. miR319, miR167, miR164, and miR159). Notable changes were observed in the level of auxins [indole-3-acetic acid (IAA), indole-3- butyric acid, and naphthalene acetic acid], jasmonates [jasmonic acid (JA) and methyl jasmonate], and abscisic acid. The exogenous supply of JA and IAA improved growth of plants under As stress and altered expression of miR167, miR319, and miR854, suggesting interplay of hormones and miRNAs in the regulation of As response. In conclusion, the present work demonstrates the role of miRNAs and associated mechanisms in the plants response towards As stress.

Effect of variable sulfur supply on arsenic tolerance and antioxidant responses in Hydrilla verticillata (L.f.) Royle

In the present study, Hydrilla verticillata plants were exposed to arsenate (AsV; 50 microM) and arsenite (AsIII; 5 microM) under variable S supply: deficient (2 microM S, -S), normal (1 mM S, +S) and excess (2 mM S, +HS). Arsenic accumulation (microg g(-1) dw) in +HS plants was about 2-fold higher upon exposure to both AsV (30) and AsIII (50) than that observed in +S (12 & 24) and -S (14 & 26) plants. Despite lower As accumulation, -S plants experienced the maximum oxidative stress owing to an inadequate response of enzymatic and molecular antioxidants and significant decline in total thiols and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG). By contrast +HS plants had significant increase in total thiols and an improved redox status, did not demonstrate any negative impact to antioxidants except catalase and hence experienced the least increase in oxidative stress parameters. In conclusion, an increase in S supply to plants may improve their accumulation capacity for As through enhanced tolerance caused by a positive effect on thiol metabolism and antioxidant status of the plants.

Grease immobilized on polyethyleneimine cotton cloth

Jack bean urease was immobilized on polyethylenimine-coated cotton cloth by adsorption following by crosslinking with dimethyl suberimidate. Of the various methods used, crosslinking with dimethyl suberimidate was found to stabilize the enzyme with minimal inactivation. Cloth-bound urease showed a shift in pH optimum towards the acidic side without appreciable change in temperature optimum and thermostability. Cloth-bound urease could be used repeatedly for urea hydrolysis without appreciable loss in activity. Alternatively, urease cloth could be stitched in the form of a bag containing ammonia adsorbent and used for urea hydrolysis with simultaneous removal of ammonia.

Mechanisms of Arsenic Tolerance and Detoxification in Plants and their Application in Transgenic Technology: A Critical Appraisal

Arsenic (As) contamination of the environment has emerged as a serious problem. Consequently, there is an urge to understand plants’ responses to As. The analysis of various hypertolerant and hyperaccumulator plants and comparison of their responses with non-tolerant and nonaccumulators have provided valuable information about the mechanisms of As tolerance and detoxification. Therefore, we understand why most of the pteridophytes are able to hyperacumulate As, why it is difficult to find hyperaccumulators among angiosperms and why rice is able to translocate As to its grains more efficiently than any other cereal crop. This information can be employed to generate As hyperaccumulators in angiosperms and to develop safe cultivars of rice for human consumption through biotechnological approaches. Although measurable success, in terms of application in the field, has so far not been achieved, transgenic research has yielded promising results, which shed light on the approaches to be taken up in future endeavor. In this review, we discuss the mechanisms of As tolerance and detoxification in plants and transgenic research conducted.

The effect of arsenic on pigment composition and photosynthesis in Hydrilla verticillata

The present study evaluated the effects of 100 and 500 μM arsenate (Na2HAsO4) on pigment composition and photosynthesis in Hydrilla verticillata (L.f.) Royle. Arsenic accumulation increased in concentration and duration dependent manner. The maximum accumulation [568 μg(As) g−1(d.m.)] was observed at 500 μM concentration and 96-h exposure. This concentration led to a significant decline in chlorophyll a content and PS II efficiency during the whole experiment, and in chlorophyll b and carotenoids after 96 h, but no significant changes in photosynthetic pigments were noticed at 100 μM arsenate. Net photosynthetic rate, electron transport rate, and water use efficiency declined whereas transpiration rate increased, and stomatal conductance and photochemical quenching did not show any effect or increased. The content of reactive oxygen species increased and content of reduced ascorbate declined at 500 μM arsenate in comparison to the control.

Thiourea orchestrates regulation of redox state and antioxidant responses to reduce the NaCl-induced oxidative damage in Indian mustard (Brassica juncea (L.) Czern.).

Thiourea (TU) has been found to enhance the stress tolerance of plants in our earlier field trials. In the present study, the TU mediated effect on the redox and antioxidant responses were studied in response to salinity (NaCl) stress in Indian mustard (Brassica juncea (L.) Czern.) seedlings. Biochemical analyses of reactive oxygen species (ROS) and lipid peroxidation revealed that TU supplementation to NaCl brought down their levels to near control values as compared to that of NaCl stress. These positive effects could be correlated to the significant increases in the 1,1-diphenyl-2-picrylhydrazyl (DPPH)-radical scavenging activity, in the levels of reduced glutathione (GSH) and GSH/GSSG (reduced/oxidized glutathione) ratio and in the activities of superoxide dismutase (SOD; EC 1.1.5.1.1) and glutathione reductase (GR; EC 1.6.4.2) in NaCl+TU treatment as compared to that of NaCl treatment. Further, TU supplementation allowed plants to avoid an over-accumulation of pyridine nucleotides, to stimulate alternative pathways (through higher glycolate oxidase activity; EC 1.1.3.15) for channeling reducing equivalents and thus, to maintain the redox state to near control levels. These positive responses were also linked to an increased energy utilization (analyzed in terms of ATP/ADP ratio) and presumably to an early signaling of the stress through stimulated activity of ascorbate oxidase (EC 1.10.3.3), an important component of stress signaling. A significant reduction observed in the level of sodium ion (Na(+)) accumulation indicated that TU mediated tolerance is attributable to salt avoidance. Thus, the present study suggested that TU treatment regulated redox and antioxidant machinery to reduce the NaCl-induced oxidative stress.

A simple approach for the simultaneous isolation and immobilization of invertase using crude extracts of yeast and Jack bean meal

Crude cell-free extract of yeast cells was mixed with sufficient amount of Jack bean meal extract so as to precipitate all the invertase. The precipitate was then cross-linked using 2% glutaraldehyde retaining over 60% of the activity. The immobilized invertase could be reused for over ten batches without loss in activity.

Phytoremediation of Metals and Radionuclides

Phytoremediation is an emerging technology for contaminated sites and is attractive due to its low cost, high public acceptance and environmental friendliness nature. It is not a panacea for all waste problems, but a supplement to the existing technologies. The technology has been demonstrated, but not yet commercially exploited. More research background for development of plant tailored for remediation needs use of genetic engineering. The concept of manipulating plant genes for toxic metal uptake is today a cutting edge research area. The likelihood of public acceptance of genetically engineered plants for phytoremediation will be welcomed, since it will clean up the environment of toxic metals. No doubt phytoremediation technology has attracted a great deal of attention in recent years and it is expected that phytoremediation will capture a significant share of the environmental market in the coming years.

Evaporation induced self assembled microstructures of silica nanoparticles and Streptococcus lactis cells as sorbent for uranium (VI)

An assembled microstructure of silica nanoparticles and Streptococcus lactis (S. lactis) cells has been synthesized by evaporation induced self assembly, with the objective of its application in bioremediation. Different morphologies have been realized by tuning the physico-chemical conditions of the assembly process. The potential of these microstructures in removal of uranium (VI) has been evaluated. Morphology dependent uptake has been demonstrated and maximum uptake was seen for the spray dried doughnut shaped microstructure (SDSM). For a fixed morphology, the variation in uptake varies with solution pH, contact time, temperature and initial uranium (VI) concentration. The U (VI) removal was significantly rapid, with more than 85 ± 2% of total uptake in 10 min. The maximum sorption capacity (qmax) of U (VI) at pH 5.0 and temperature 298 K was 169.5 mg/g using SDSM as sorbent. The kinetic data of adsorption of U (VI) are best described by a pseudo-second-order kinetic model. Calculated thermodynamic parameters reveal an endothermic and a spontaneous adsorption process. The present work opens up the possibility of a means for the functionalization of silica microstructures through the incorporation of micro-organism and the potential for the use of these functionalized materials for bioremediation.