Browsing by Subject "Glutathione transferase"
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Item Analysis of an Arabidopsis mutant with altered stress responses(Texas Tech University, 2003-12) Shen, YinPlants face a variety of conditions that cause biotic and abiotic stress. Since plants are sessile, and therefore cannot move to escape stressful conditions, they have evolved complex strategies to survive harsh environments. One such strategy is the ability to quickly alter the expression of genes, which, in effect, acclimates the plant. Glutathione S-transferases (GST) are an example of these genes that are induced under stressful conditions. In order to identify the mechanisms that regulate stress responsive gene expression, I used a genetic strategy to identify stress signaling mutants in which the luciferase (LUC) reporter was expressed under control of the stressresponsive Arabidopsis GST6 promoter. After chemical mutagenesis by ethyl methanesulfonate (EMS), a number of potential mutants that affect the expression of the GST6:LUC reporter gene, and presumably, the stress signaling pathways were isolated. One of the mutants, cdg6 (constitutively down-regulated GST6), is dominant and has altered responses to abscisic acid (ABA), ethylene, and salicylic acid (SA). In addition, physiological studies of cdg6 mutant plants showed that the gene is not involved in the ethylene signaling or synthesis pathways. A transcriptional profile of cdg6 using microarray analysis gave us a genome-wide view of gene expression alterations in mutant plants compared to the wild type plants. This analysis showed that endogenous GST genes are down regulated in cdg6, while a number of defense related genes such as chitinase were up regulated. These data indicate that cdg6 may represent a mutation in a gene that regulates defense responses.Item Analysis of glutathione S-transferase (GST) gene expression in transgenic plants and its effects on environmental stress(Texas Tech University, 1998-08) Kang, Won-HeePlants cannot escape from biotic and abiotic stress factors such as extreme temperatures, high light intensity, drought, UV radiation, heavy metals, and pathogen attack. Anthropogenous stress factors, such as herbicides, also affect or block metabolism, growth, and development, and is being used every year. Plants have versatile detoxification systems to counter the phytotoxicity of a wide range of natural and synthetic compounds, which are present in the environment. Glutathione S-transferases (GSTs) are the enzymes that detoxify natural and exogenous toxic compounds by conjugation with glutathione. Glutathione, an endogenous tripeptide, is important as a reducing agent, nucleophilic scavenger, and alleviate the chemical toxicity in the plants by the reaction of GST. GSTs play an important role in the phase Ii of conjugation with xenobiotics, and have another role as glutathione peroxidase. Glutathione conjugates are can be transported to the vacuoles or apoplast and are generally much less toxic than the parent compounds. Oxygen radicals are also highly harmful to the cell components. Those toxic reactive oxygen species damage DNA, lipid layer, and proteins. Many GSTs can also act as glutathione peroxidases to sacvenge toxic peroxides from cells. A cDNA named Gh-5 was isolated from cotton fiber cDNA library, using PCR-based cloning methods. Analysis of this cDNA revealed high sequence similarity with other plant GSTs. Expression of Gh-5 in E. coli resulted in protein extracts with high GST activity. Overexpression of Gh-5 in tobacco has led to about a two-fold increase in GST specific activity compared to the nonexpressing control plants. These results indicate that Gh-5 encodes an active GST both bacterial and in plant cells. Antisense GST constructs were also developed to deactivate native cotton GST and to evaluate the effect of the decreased enzyme in cotton plants. In order to determine whether GST overexpression could confer protection to plants against oxidative stresses, transgenic plants were exposed to herbicides, salinity, low temperature, heavy metals and photooxidation. The GST overexpressing plants showed enhanced seedling tolerance to low temperature and salinaty. These results indicate that increased level of GST can protect plants from certain types of environmental stresses.Item Molecular analysis and expression of glutathione S-transferase-coding genes in tobacco(Texas Tech University, 1996-12) Roxas, Virginia P.Glutathione S-transferases (GSTs: EC 2.5.1.18) are enzymes that detoxify xenobiotic compounds by covalently linking glutathione to a substrate, forming a glutathione conjugate. Two auxin-responsive cDNAs (Nt 107 and parB) that code for GSTs were Isolated from 2,4-D (2,4-dichlorophenoxyacetic acid)-treated tobacco (Nicotiana tabacum cv. Xanthi) suspension culture cells using reverse transcription polymerase chain reaction. Expression of Nt 107 in Escherischia coli resulted in >300-fold increase in GST specific activity, demonstrating that Nt 107 encodes an active GST. E. coli cultures that express Nt 707 also exhibited glutathione peroxidase (GPX: EC 1.11.1.9) activity against the substrates cumene hydroperoxide, hydrogen peroxide and tert-butyl hydroperoxide. These findings indicate that Nt 107 is likely to be actively involved in the protection against cell stress. To determine the factors that affect the expression of Nt 107, we have analyzed its response to a wide variety of factors in the wild type tobacco. Stress-signaling compounds that include abscisic acid, hydrogen peroxide, methyl jasmonate and salicylic acid; heavy metals CuSO^ and FeS04; and salt were found to induce Nt 707 expression in a concentration-dependent manner, indicating that Nt 107 participates in the responses of plants to stress conditions.