Pallavi Sharma

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

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.

Lead toxicity in plants

A contaminacao de solos por metais pesados e de ocorrencia generalizada como resultado das atividades humana, agricola e industrial. Entre os metais pesados, o chumbo (Pb) e um poluente potencial que, prontamente, se acumula nos solos e sedimentos. Apesar de nao ser um elemento essencial para as plantas, e facilmente absorvido e acumulado em diferentes partes delas. A absorcao de Pb e regulada pelo pH, tamanho de particulas e capacidade de troca de cations dos solos, assim como pela exsudacao e outros parâmetros fisicoquimicos. Excesso de Pb causa varios sintomas de toxicidade em plantas, por exemplo: reducao de crescimento, clorose e escurecimento do sistema radicular. Pb inibe a fotossintese, altera a nutricao mineral e o balanco hidrico, modifica o estado hormonal e afeta a estrutura e permeabilidade da membrana. Esta revisao aborda varios efeitos morfologicos, fisiologicos e bioquimicos da toxicidade de Pb e tambem as estrategias adotadas pelas plantas para a destoxificacao e o desenvolvimento de tolerância ao Pb. Mecanismos de destoxificacao ao Pb incluem o sequestro de Pb no vacuolo, sintese de fitoquelatinas e o acoplamento a glutationa e aminoacidos, etc. A tolerância ao Pb esta associada a capacidade das plantas a restringir o metal a parede celular, sintese de osmolitos, e ativacao do sistema antioxidante de defesa. Remediacao de solos contaminados com Pb usando as tecnologias de fitorremediacao e rizofiltracao parecem ter grande potencial para a limpeza de solos contaminados com esse metal pesado.

Differential response of arsenic stress in two varieties of Brassica juncea L.

Present study showed the toxicity caused by Arsenite (As(III)) and its detoxification responses in two varieties (Varuna and Pusa Bold) of Brassica juncea. Comparisons were made in leaves and roots of both the varieties, which showed that the accumulation pattern in both the varieties were dose and duration dependent, being more in roots for two days and in leaves for four days. Increase/decrease of antioxidant enzymes activities (SOD, CAT, GPX) showed not much changes at the given concentrations except that the enzyme activities showed significant increase at the lower concentrations. Semi quantitative RT-PCR analysis of PCS showed more expression of its transcript in P. Bold as compared to Varuna variety due to As(III) stress. The analysis of isoenzyme pattern in leaves of P. Bold showed five and two major bands of SOD and GPX, respectively. As(III) treatment leads to the activation of MAPK activity indicating role of this important cascade in transducing As(III) mediated signals. The data presented indicates the differential responses in both the varieties and also that the increased tolerance in P. Bold may be due to the defensive role of antioxidant enzymes, induction of MAPK and up regulation of PCS transcript which is responsible for the production of metal binding peptides.

Differential regulation of rice mitogen activated protein kinase kinase (MKK) by abiotic stress

Mitogen activated protein kinase cascade plays a crucial role in various biotic and abiotic stresses, hormones, cell division and developmental processes. MAP kinase kinase being integral part of this cascade performs an important function of integrating upstream signals to mitogen activated protein kinase for further appropriate cellular responses. We here report cloning of five MAP kinase kinase members from Oryza sativa indica cultivar var. Pusa Basmati 1, namely MAP kinase kinases 1, 3, 4, 6 and 10-2. All these members, except MKK10-2 possess fully canonical motif structures of MAP kinase kinase. The deduced amino acid sequence showed changes at certain position within japonica and indica variety of rice. Analysis of transcript regulation by quantitative real time PCR revealed that these five members are differentially regulated by cold, heat, salinity and drought stresses. MAP kinase kinases 4 and 6 are strongly regulated by cold and salt stresses while MAP kinase kinase 1 is regulated by salt and drought stresses. MAP kinase kinase 10-2 is regulated only by cold stress. The study provides the indication of involvement of specific MAP kinase kinase in different abiotic stress signaling and also possible cross talks that exist during the signaling processes.

A Light Scattering Study of the Interaction of Fibroblast Growth Factor (FGF) with its Receptor

Light scattering technique has been used to study the interaction between fibroblast growth factor (FGF) and its receptor. In this study, a general mathematical model has been developed where the concentration of product formed by the interaction of two proteins and its dependence on the initial concentration of interacting proteins have been determined using laser light scattering. Calculated hydrodynamic diameters reveal that both human fibroblast growth factor (hFGF-1) and its receptor domain (D2 domain) exist as monomers in solution. Titration of hFGF-1 and the D2 domain of FGFR show that they interact in a 1:1 stoichiometry in solution. The binding stoichiometry does not depend on the concentrations of the interacting proteins. The results of this study, for the first time to our knowledge, provide an unambiguous evidence that the 2:2 binary complex of FGF and FGFR observed in the crystal structures of the FGF-FGFR complex (in the absence of heparin) is possibly a crystallization artifact.

Functional Genomics For Crop Improvement

Plant breeding has had a tremendous influence on crop improvement. However, due to dwindling germplasm resources, identification of variability for incorporation into new cultivars is becoming more difficult. Therefore, there has been recourse to alternative approaches including mutagenesis, tissue culture and genetic transformation to aid breeding programs. Furthermore, with the vast repertoire of genome-wide data from different expression profiling techniques such as microarrays, more subtle understanding of gene expression is being obtained and is further helping plant breeders to entertain a different selection approach based on expression quantitative traits to maximize combinations of genes capable of conferring high performance. In this chapter, we review some of the aspects of plant breeding and the influence functional genomics has on breeding programs. Some of the challenges to functional genomics and breeding come from establishment of high-throughput transformation systems to assess gene function, which is limiting functional characterization of numerous genes in their respective crops. Therefore, this chapter also focuses on the need to gain better understanding of the development of gene transfer systems for crop plants to make use of the array of available gene information data.

Single Nucleotide Polymorphisms in B-Genome Specific UDP-Glucosyl Transferases Associated with Fusarium Head Blight Resistance and Reduced Deoxynivalenol Accumulation in Wheat Grain

An in vitro spike culture method was optimized to evaluate Fusarium head blight (FHB) resistance in wheat (Triticum aestivum) and used to screen a population of ethyl methane sulfonate treated spike culture-derived variants (SCDV). Of the 134 SCDV evaluated, the disease severity score of 47 of the variants was ≤30%. Single nucleotide polymorphisms (SNP) in the UDP-glucosyltransferase (UGT) genes, TaUGT-2B, TaUGT-3B, and TaUGT-EST, differed between AC Nanda (an FHB-susceptible wheat variety) and Sumai-3 (an FHB-resistant wheat cultivar). SNP at 450 and 1,558 bp from the translation initiation site in TaUGT-2B and TaUGT-3B, respectively were negatively correlated with FHB severity in the SCDV population, whereas the SNP in TaUGT-EST was not associated with FHB severity. Fusarium graminearum strain M7-07-1 induced early expression of TaUGT-2B and TaUGT-3B in FHB-resistant SCDV lines, which were associated with deoxynivalenol accumulation and reduced FHB disease progression. At 8 days after inoculation, deoxynivalenol concentration varied from 767 ppm in FHB-resistant variants to 2,576 ppm in FHB-susceptible variants. The FHB-resistant SCDV identified can be used as new sources of FHB resistance in wheat improvement programs.

A Study of Fibroblast Growth Factor and Its Receptor Complex Using Light Scattering

Dynamical light scattering technique was used to study the interaction of fibroblast growth factor and its receptor proteins in solution.