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. Efficient 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 paper, 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.

https://downloads.hindawi.com/archive/2012/217037.pdf

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Metal contamination issues are becoming increasingly common in India and elsewhere, with many documented cases of metal toxicity in mining industries, foundries, smelters, coal-burning power plants and agriculture. Heavy metals, such as cadmium, copper, lead, chromium and mercury are major environmental pollutants, particularly in areas with high anthropogenic pressure. Heavy metal accumulation in soils is of concern in agricultural production due to the adverse effects on food safety and marketability, crop growth due to phytotoxicity, and environmental health of soil organisms. The influence of plants and their metabolic activities affects the geological and biological redistribution of heavy metals through pollution of the air, water and soil. This article details the range of heavy metals, their occurrence and toxicity for plants. Metal toxicity has high impact and relevance to plants and consequently it affects the ecosystem, where the plants form an integral component. Plants growing in metal-polluted sites exhibit altered metabolism, growth reduction, lower biomass production and metal accumulation. Various physiological and biochemical processes in plants are affected by metals. The contemporary investigations into toxicity and tolerance in metal-stressed plants are prompted by the growing metal pollution in the environment. A few metals, including copper, manganese, cobalt, zinc and chromium are, however, essential to plant metabolism in trace amounts. It is only when metals are present in bioavailable forms and at excessive levels, they have the potential to become toxic to plants. This review focuses mainly on zinc, cadmium, copper, mercury, chromium, lead, arsenic, cobalt, nickel, manganese and iron.

Heavy metals, occurrence and toxicity for plants: a review

Phytoremediation of heavy metals—Concepts and applications

Response to cadmium in higher plants

Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.

Heavy metals in soils : trace metals and metalloids in soils and their bioavailability

Eighteen barley isolates of Bipolaris sorokiniana belonging to wild and clonal type of black, mixed and white subpopulations were quantitatively assayed for their melanin content and aggressiveness with respect to production of some of the extracellular enzymes such as cellulase, pectinase, amylase and protease. Cellulase and pectinase constituted major portion of the enzymes recovered from the black, mixed and white isolates. Enzyme production and aggressiveness were relatively higher in melanin devoid or low melanin isolates. The melanin deficient isolates were also differentiated from black and mixed isolates on the basis of variation in internal transcribed spacer region of the ribosomal DNA. Higher enzyme productions positively correlated with area under disease progress curve (AUDPC) and lesion development. Melanin content was negatively correlated with extracellular enzymes and aggressiveness of the isolates. Based on melanin content, lesion size, AUDPC and extracellular enzymes, the isolates were grouped in two major clusters (I and II) with further division of cluster II into two sub-clusters (II-A and II-B). The results appears to indicate a possible role of melanin in release of extracellular enzymes and hence in evolution and selection of aggressive isolates of B. sorokiniana in barley.

Role of Melanin in Release of Extracellular Enzymes and Selection of Aggressive Isolates of Bipolaris sorokiniana in Barley

Nitrate reductase from rice seedlings: Partial purification, characterization and the effects of in situ and in vitro NaCl salinity

Cadmium is a well known toxic heavy metal, which has various detrimental effects on plant system. In plants an important enzyme involved in the production of nitric oxide, nitrate reductase, is also affected by cadmium toxicity. According to many studies cadmium has an inhibitory effect on nitrate reductase activity. Similar effect of cadmium was found in our study where an inhibitory effect of cadmium on nitrate reductase activity was noted. However, the mechanism behind this inhibition has not been explored. With the help of homology, 3-D structure of rice-nitrate reductase is modeled in this study. Its binding with nitrate, nitrite and cadmium metal in silico has been explored. The bonds formed between the enzyme-substrate complex, enzyme-cadmium and differences in interactions in presence of cadmium has been studied in detail. The present study should help in understanding the modeled structure of rice-nitrate reductase in 3-D which may in turn guide enzyme related studies in silico. The present study also provides an insight as to how cadmium interacts with nitrate reductase to alter the enzyme activity.

Reduced Activity of Nitrate Reductase Under Heavy Metal Cadmium Stress in Rice: An in silico Answer.

Knowledge of rice genome brings new dimensions to the management of abiotic stresses; however, gene sequences in the rice genome are yet to be assigned structure and function. Hydrogen peroxide, salicylates and jasmonates act as signal molecules in plants employing common machinery to manage abiotic stress. The present work is primarily focused to assign a structurefunction relationship by modeling of the hypothetical proteins of SA-JA signaling pathway known in Arabidopsis thaliana and compare them with corresponding proteins in rice in silico. Thirteen known gene sequences with their encoded proteins for SA/JA pathway in model plant A. thaliana were obtained and similar gene sequences from rice were retrieved at NCBI. Five rice gene sequences Os09g0392100, Os03g0233200, OsJ_33269, OsJ_23610 and Os01g0194300 resulted in hypothetical protein products with unknown structure and function. Modeling and comparison of 5 proteins from rice and Arabidopsis showed 73 - 98% identity with acceptable RMSD values of 0.6 - 1.7 upon superimposition. Results suggest conserved nature of these proteins during evolution. The hypothetical protein from rice contains similar functional protein domain as that in A. thaliana and therefore are likely to perform similar functions in rice. There is a cross talk between the genes in SA/JA pathway wherein Os09g0392100 or EDS1, Os03g0233200 or PR5, OsJ_33269 or PAD4 and OsJ_23610 or SFD-1 activates the pathway and Os01g0194300 or NPR1 inhibit the pathway. Further investigation through wet-lab experiments are in progress to look into suppression/activation of the genes of SAJA signaling in rice plants exposed to abiotic stress.

/pdf/in-search-of-function-for-hypothetical-proteins-encoded-by-2gmd6yoiqn.pdf

In search of function for hypothetical proteins encoded by genes of SA-JA pathways in Oryza sativa by in silico comparison and structural modeling.

Role of salicylic acid in plants grown under metal contaminated soil is not yet understood. To investigate if signaling by Cd-induced H2O2 or SA, collide or integrate, rice cv. HUR3022, grown for 3, 7 and 10 day under 50 µM Cd/SA alone or in combination were studied. Dynamic distribution of Cd2+ and SA, cell viability, time-dependent changes in H2O2 levels, free proline, chlorophyll, ascorbate and glutathione pools and altered antioxidant enzymes in roots/shoots of rice were observed. Exogenous SA decelerated cell-death in Cd-stressed rice playing a positive role in protection against injury. Cd led to elevated activities of superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase and phenylalanine ammonia lyase and lowered catalase and glutathione reductase activities in roots and shoots of rice seedlings. By contrast, SA + Cd2+ reversed the trend of enzyme activities, levels of non-enzymatic antioxidants and GSH in roots/shoots suggesting alleviation of Cd-induced oxidative damage in rice. Suppression of Cd-uptake in presence of SA suggest an epistatic effect of SA-signal over Cd-induced ROS-signal in rice roots. No additive effects of SA or H2O2 signals were noted in Cd-stressed rice. Results indicate integration of different signals and SA-enhanced Cd2+ tolerance due to SA-regulated Cd2+ uptake as well as the SA-elevated enzymatic and non-enzymatic antioxidant pool in rice. Role of salicylic acid in rice plants grown under Cd-contaminated soil was studied. Cd-induced H2O2 or SA, signals both collide and/or integrate. Dynamic distribution of Cd2+ and SA, cell viability, time-dependent changes in H2O2 levels, free proline, chlorophyll, ascorbate and glutathione pools appear. Suppression of Cd-uptake in presence of SA were noted. Integration of different signals, SA-induced Cd2+ tolerance and SA-elevated enzymatic and non-enzymatic antioxidant pool in rice was observed.

Kavita Shah

Papers

Role of Melanin in Release of Extracellular Enzymes and Selection of Aggressive Isolates of Bipolaris sorokiniana in Barley

Nitrate reductase from rice seedlings: Partial purification, characterization and the effects of in situ and in vitro NaCl salinity

Reduced Activity of Nitrate Reductase Under Heavy Metal Cadmium Stress in Rice: An in silico Answer.

In search of function for hypothetical proteins encoded by genes of SA-JA pathways in Oryza sativa by in silico comparison and structural modeling.

Evidences for suppression of cadmium induced oxidative stress in presence of sulphosalicylic acid in rice seedlings