BHU Institutional Repository :: Browsing by Author "Sharma, Pallavi"

Browsing by Author "Sharma, Pallavi"

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Arsenic Toxicity and Tolerance Mechanisms in Crop Plants
(Taylor and Francis, 2014) Sharma, Pallavi; Jha, Ambuj Bhushan; Dube, Rama Shanker
Arsenic (As) is a ubiquitous element present in the environment. Although metalloid, it is often grouped among the toxic metals. It is the 20th most abundant element in the Earth’s crust, with an average concentration ranging from 1.5 to 5 mg/kg (Cullen and Reimer, 1989). In noncontaminated soils, arsenic concentrations typically range from 0.2 to 40 mg/kg (World Health Organization, 1981), whereas in contaminated soils, arsenic concentrations as high as 100-2500 mg/kg have been reported (World Health Organization, 1981; Diaz-Barriga et al., 1993; Vaughan, 1993). Arsenic can enter soil through both natural processes such as weathering and erosion of arsenic-bearing rocks (Alloway, 1990; Yan-Chu, 1994) and anthropological activities such as mining, smelting of ores, coal combustion, release of arsenic-laden liquid and solid wastes from industrial plants, irrigation with arsenic-contaminated water, and use of arsenic-based pesticides, herbicides, and fertilizers (reviewed by Smith et al., 1998; Mahimairaja et al., 2005). Arsenic is a signicant contaminant of soils and groundwater in many regions of the world including Argentina, Bangladesh, Chile, Mexico, China, Hungary, India, and Vietnam (Mahimairaja et al., 2005 and references therein), and the situation is worst in the densely populated oodplains and river deltas of South and Southeast Asia (Nordstrom, 2002; Brammer and Ravenscroft, 2009). Arsenic leads to stimulation of plant growth at low concentrations (Woolson et al., 1971; Carbonell-Barrachina et al., 1997; Miteva, 2002; Garg and Singla, 2011); however, at high concentrations, it not only exerts toxic effects on plants and animals but may pose severe health complications for humans and animals. © 2014 by Taylor & Francis Group, LLC.
Ascorbate peroxidase from rice seedlings: Properties of enzyme isoforms, effects of stresses and protective roles of osmolytes
(2004) Sharma, Pallavi; Dubey, R.S.
Two isoforms of ascorbate peroxidase, namely, APX 1 and APX 2 with subunit molecular weight of 28.5 and 34 kDa, respectively, were purified from leaves of 15-day grown rice (Oryza sativa L.) plants. The molecular and enzymatic properties of the two isoforms differed significantly but both belonged to the class of ascorbate specific heme peroxidases and were inhibited by thiol reagents. The two isozymes were separated from each other at the DEAE-Sephacel chromatography step of purification and were named APX 1 and APX 2 in the order of elution in the chromatography. APX 2 accounted for 74% of the total activity. The Km values of APX 1 and APX 2 for ascorbate were 400 and 200 μM and those for hydrogen peroxide were 33 and 76 μM, respectively. Both isoforms had very high preference for ascorbate as electron donor. pH optima for APX 1 and APX 2 were 6.5 and 7.0, respectively. Activity of both isoforms was completely lost by heat treatment at 80°C for 20 min or in presence of 150 mM NaCl in the assay medium. A 40% polyethylene glycol (PEG-6000) in the assay medium led to about 50% inhibition in the activity of APX 1 and 65% inhibition of APX 2 with an increase in enzyme Km values. Incorporation of 1 M proline, glycine betaine or sucrose in presence of PEG in the assay medium led to a pronounced restoration in enzyme activity with decrease in Km values. Glycine betaine appeared to be an effective protectant for both isoforms under in vitro water stressed conditions. APX 2 appeared to be more sensitive to the metals Ni, Al and As when compared to APX 1. When rice seedlings were raised in sand cultures in nutrient solution containing 1 mM Al2(SO4)3, during a 5-20 day growth period about 0.5-1.3 times higher activity of APX was observed compared to the activity in controls. Similarly, rice seedlings subjected to polyethylene glycol induced water deficit for 24 h showed elevated APX activity compared to unstressed seedlings. Ascorbate peroxidase in rice seedlings appears to have an important role in detoxification of H 2O2 under abiotic stressful conditions. © 2004 Elsevier Ireland Ltd. All rights reserved.
Drought induces oxidative stress and enhances the activities of antioxidant enzymes in growing rice seedlings
(2005) Sharma, Pallavi; Dubey, Rama Shanker
When rice seedlings grown for 10 and 20 days were subjected to in vitro drought stress of -0.5 and -2.0 MPa for 24 h, an increase in the concentration of superoxide anion (O2 .-), increased level of lipid peroxidation and a decrease in the concentration of total soluble protein and thiols was observed in stressed seedlings compared to controls. The concentration of H2O2 as well as ascorbic acid declined with imposition of drought stress, however glutathione (GSH) concentration declined only under severe drought stress. The activities of total superoxide dismutases (SODs) as well as ascorbate peroxidase (APX) showed consistent increases with increasing levels of drought stress, however catalase activity declined. Mild drought stressed plants had higher guaiacol peroxidase (GPX) and chloroplastic ascorbate peroxidase (c-APX) activity than control grown plants but the activity declined at the higher level of drought stress. The activities of enzymes involved in regeneration of ascorbate i.e. monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were higher in drought stressed plants compared to controls. Results suggest that drought stress induces oxidative stress in rice plants and that besides SOD, the enzymes of ascorbate-glutathione cycle, which have not been studied in detail earlier under stressful conditions, appear to function as important component of antioxidative defense system under drought stress. © Springer 2005.
Effect of abiotic stresses on growth, metabolic alterations and tolerance mechanisms in rice crop
(Nova Science Publishers, Inc., 2009) Sharma, Pallavi; Jha, Ambuj Bhushan; Dubey, R.S.
Rice is a staple food crop for the majority of world population. Abiotic stressful conditions of the environment such as salinity, drought, heat, chilling, anaerobiosis, metal toxicity impose limitations on productivity of rice in the regions which are prone to such constraints. The manifestations of these stresses include non-expression of full genetic potential, differential transcription of many genes, induction of stress responsive genes leading to cellular metabolic changes, alteration in activity behaviours of many enzymes, overproduction of several compatible metabolites like amino acids, sugars, polyamines, phytochelatins, organic acids, increased synthesis of many enzymes and stress specific proteins. Salinity and drought are prime stressful conditions for rice crop in arid and semi arid regions of the world. Changes in temperature rhythm impose heat or chilling injury. Soil flooding or submergence causes oxygen deprivation leading to anaerobic stress. Metal ions such as Pb, Cd, Hg, As, Ni are key pollutants of the soil, whereas Al toxicity is a problem in acid upland soils. Most of the abiotic stresses cause overproduction of reactive oxygen species (ROS) within the cell which cause oxidative damage to membranes and biomolecules. Increased accumulation of compatible solutes, overproduction of antioxidative enzymes, overexpression of transcription factors have been shown to confer tolerance in rice plants to a wide range of stresses like salinity, drought and low temperature. Stress induced gene products those involved in stress tolerance and those involved in signal transduction or as transcription regulators have served as basis to engineer stress tolerant plants. To contribute to food security and sustainability in rice production, it is essential to produce stress tolerant rice plants suitable for cultivation in stress prone areas. This needs a detail understanding of physiological and molecular mechanisms associated with stress tolerance more specially gene products involved in stress tolerance and signal transduction. Transcriptome profiling of rice seedlings has helped in great way in understanding how rice plants respond to abiotic stresses. Successful attempts have been made to produce transgenic rice plants tolerant to different abiotic stresses. However, with the rapid progress in the areas of functional genomics, proteomics and metabolomics a more improved understanding of novel stress responsive genes and their expression under various stresses is anticipated which will provide the basis of new strategies to produce genetically engineered rice plants tolerant to a single or multiple of abiotic stresses. © 2009 Nova Science Publishers, Inc.
Involvement of oxidative stress and role of antioxidative defense system in growing rice seedlings exposed to toxic concentrations of aluminum
(2007) Sharma, Pallavi; Dubey, R.S.
When seedlings of rice (Oryza sativa L.) cultivar Pant-12 were raised in sand cultures containing 80 and 160 μM Al3+ in the medium for 5-20 days, a regular increase in Al3+ uptake with a concomitant decrease in the length of roots as well as shoots was observed. Al3+ treatment of 160 μM resulted in increased generation of superoxide anion (O 2 -) and hydrogen peroxide (H2O2), elevated amount of malondialdehyde, soluble protein and oxidized glutathione and decline in the concentrations of thiols (-SH) and ascorbic acid. Among antioxidative enzymes, activities of superoxide dismutase (SOD EC 1.15.1.1), guaiacol peroxidase (Guaiacol POX EC 1.11.1.7), ascorbate peroxidase (APX EC 1.11.1.11), monodehydroascorbate reductase (MDHAR EC 1.6.5.4), dehydroascorbate reductase (EC 1.8.5.1) and glutathione reductase (EC 1.6.4.2) increased significantly, whereas the activities of catalase (EC EC 1.11.1.6) and chloroplastic APX declined in 160 μM Al3+ stressed seedlings as compared to control seedlings. The results suggest that Al3+ toxicity is associated with induction of oxidative stress in rice plants and among antioxidative enzymes SOD, Guaiacol POX and cytosolic APX appear to serve as important components of an antioxidative defense mechanism under Al3+ toxicity. PAGE analysis confirmed the increased activity as well as appearance of new isoenzymes of APX in Al3+ stressed seedlings. Immunoblot analysis revealed that changes in the activities of APX are due to changes in the amounts of enzyme protein. Similar findings were obtained when the experiments were repeated using another popular rice cv. Malviya-36. © 2007 Springer-Verlag.
Lead toxicity in plants
(Sociedade Brasileira de Fisiologia Vegetal, 2005) Sharma, Pallavi; Dubey, Rama Shanker
Contamination of soils by heavy metals is of widespread occurrence as a result of human, agricultural and industrial activities. Among heavy metals, lead is a potential pollutant that readily accumulates in soils and sediments. Although lead is not an essential element for plants, it gets easily absorbed and accumulated in different plant parts. Uptake of Pb in plants is regulated by pH, particle size and cation exchange capacity of the soils as well as by root exudation and other physico-chemical parameters. Excess Pb causes a number of toxicity symptoms in plants e.g. stunted growth, chlorosis and blackening of root system. Pb inhibits photosynthesis, upsets mineral nutrition and water balance, changes hormonal status and affects membrane structure and permeability. This review addresses various morphological, physiological and biochemical effects of Pb toxicity and also strategies adopted by plants for Pb-detoxification and developing tolerance to Pb. Mechanisms of Pb-detoxification include sequestration of Pb in the vacuole, phytochelatin synthesis and binding to glutathione and aminoacids etc. Pb tolerance is associated with the capacity of plants to restrict Pb to the cell walls, synthesis of osmolytes and activation of antioxidant defense system. Remediation of soils contaminated with Pb using phytoremediation and rhizofiltration technologies appear to have great potential for cleaning of Pb-contaminated soils.
Modulation of nitrate reductase activity in rice seedlings under aluminium toxicity and water stress: Role of osmolytes as enzyme protectant
(Elsevier GmbH, 2005) Sharma, Pallavi; Shanker Dubey, Rama
Nitrate reductase (NR) activity in the presence of Mg2+ (NR act) representing the non-phosphorylated NR state and the activity in the presence of EDTA (NR max) representing maximum NR activity was measured in roots and shoots of 15 d grown aluminium and water stressed rice seedlings to examine changes in NR activation state due to these stresses. Seedlings subjected to a moderate water stress level of -0.5 MPa for 24 h or grown in presence of 80 μM Al3+showed decreased level of NR max but resulted in higher NR act and NR activation state. However, seedlings grown in presence of a higher level of 160 μM Al3+ showed a decline in NR act as well as NR max. With a higher water stress level of -2.0 MPa a marked decline in the levels of both NR act and NR max was observed, whereas NR activation state remained almost unaltered with severe water stress. NR activity appeared to be sensitive to H2O2, PEG-6000, NaCl and various metal salts. Incorporation of these components in the enzyme assay medium led to decreased affinity of enzyme towards its substrate with increase in Km and decrease in Vmax values. Addition of each of the osmolytes i.e. 1 mol/L proline, 1 mol/L glycine betaine or 1 mol/L sucrose in the enzyme assay medium caused a considerable protection to the enzyme against the damaging effects of stressful components. An enhanced level of proline and glycine betaine was observed in Al-stressed seedlings and sucrose in Al as well as water stressed seedlings. Results suggest that Al toxicity and water stress decrease total amount of functional NR in rice seedlings and the osmolytes proline, glycine betaine and sucrose appear to have a direct protective action on enzyme NR under stressful conditions © 2005 Elsevier GmbH. All rights reserved.
Oxidative stress and antioxidative defense systems in plants growing under abiotic stresses
(CRC Press, 2016) Sharma, Pallavi; Jha, Ambuj Bhushan; Dubey, Rama Shanker
[No abstract available]
Protein synthesis by plants under stressful conditions
(CRC Press, 2016) Sharma, Pallavi; Dubey, Rama Shanker
[No abstract available]
Reactive Oxygen Species Generation, Hazards, and Defense Mechanisms in Plants under Environmental (Abiotic and Biotic) Stress Conditions
(Taylor and Francis, 2014) Sharma, Pallavi; Jha, Ambuj Bhushan; Dubey, Rama Shanker; Pessarakli, Mohammad
Reactive oxygen species (ROS) are produced as a normal product of plant cellular metabolism. Various environmental stresses lead to excessive production of ROS causing progressive oxidative damage and ultimately cell death. Despite their destructive activity, they are well-described second messengers in a variety of cellular processes, including conferment of tolerance to various environmental stresses. Whether ROS would serve as signaling molecules or could cause oxidative damage to the tissues depends on the delicate equilibrium between ROS production and their scavenging. Efcient scavenging of ROS produced during various environmental stresses requires the action of several nonenzymatic as well as enzymatic antioxidants present in the tissues. In this review, we describe the generation, sites of production, and role of ROS as messenger molecules as well as inducers of oxidative damage. Further, the antioxidative defense mechanisms operating in the cells for scavenging of ROS overproduced under various stressful conditions of the environment have been discussed in detail. © 2014 by Taylor & Francis Group, LLC.
The efficient applications of native flora for phytorestoration of mine tailings: a pan-global survey
(Springer, 2024) Swain, Ankit Abhilash; Sharma, Pallavi; Keswani, Chetan; Minkina, Tatiana; Tukkaraja, Purushotham; Gadhamshetty, Venkataramana; Kumar, Sanjeev; Bauddh, Kuldeep; Kumar, Narendra; Shukla, Sushil Kumar; Kumar, Manoj; Dubey, Rama Shanker; Wong, Ming Hung
Mine tailings are the discarded materials resulting from mining processes after minerals have been extracted. They consist of leftover mineral fragments, excavated land masses, and disrupted ecosystems. The uncontrolled handling or discharge of tailings from abandoned mine lands (AMLs) poses a threat to the surrounding environment. Numerous untreated mine tailings have been abandoned globally, necessitating immediate reclamation and restoration efforts. The limited feasibility of conventional reclamation methods, such as cost and acceptability, presents challenges in reclaiming tailings around AMLs. This study focuses on phytorestoration as a sustainable method for treating mine tailings. Phytorestoration utilizes existing native plants on the mine sites while applying advanced principles of environmental biotechnology. These approaches can remediate toxic elements and simultaneously improve soil quality. The current study provides a global overview of phytorestoration methods, emphasizing the specifics of mine tailings and the research on native plant species to enhance restoration ecosystem services. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.

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