Glutathione Metabolic Genes Coordinately Respond to Heavy Metals and Jasmonic Acid in Arabidopsis

Abstract

Glutathione plays a pivotal role in protecting plants from environmental stresses, oxidative stress, xenobiotics, and some heavy metals. Arabidopsis plants treated with cadmium or copper responded by increasing transcription of the genes for glutathione synthesis, ␥ -glutamylcysteine synthetase and glutathione synthetase, as well as glutathione reductase. The response was specific for those metals whose toxicity is thought to be mitigated through phytochelatins, and other toxic and nontoxic metals did not alter mRNA levels. Feeding experiments suggested that neither oxidative stress, as results from exposure to H 2 O 2 , nor oxidized or reduced glutathione levels were responsible for activating transcription of these genes. Jasmonic acid also activated the same suite of genes, which suggests that it might be involved in the signal transduction pathway for copper and cadmium. Jasmonic acid treatment increased mRNA levels and the capacity for glutathione synthesis but did not alter the glutathione content in unstressed plants, which supports the idea that the glutathione concentration is controlled at multiple levels. INTRODUCTIONGlutathione (GSH), the tripeptide ␥ -glutamylcysteinylglycine, is the major source of non-protein thiols in most plant cells (Bergmann and Rennenberg, 1993). GSH plays a central role in protecting plants from environmental stresses, including oxidative stress due to the generation of active oxygen species, xenobiotics, and some heavy metals.GSH is involved in quenching reactive oxygen species (Larson, 1988; Alscher, 1989; Foyer et al., 1994b). The ascorbate/GSH cycle reduces H 2 O 2 to water (Foyer and Halliwell, 1976; Alscher, 1989). Ascorbate is also important in maintaining ␣ -tocopherol in the reduced state and therefore links GSH to the dominant free radical scavenger in membranes (Hess, 1994). Plants detoxify many organic contaminants by conjugating them or their metabolites to GSH for storage or further metabolism (Lamoureux et al., 1994). These reactions are catalyzed by glutathione S -transferases (GSTs). Plants are protected from some metals, with cadmium and copper being the most studied, by a group of ␥ -glutamylcysteine ( ␥ -EC) peptides, the phytochelatins (PCs). These molecules have the general structure ( ␥ -Glu-Cys) 2-11 -Gly. They are formed by the polymerization of GSH catalyzed by the transpeptidase phytochelatin synthase (Grill et al., 1985(Grill et al., , 1987 Chen et al., 1997). The PCs bind metals in the cytosol, and the PC metal complex is sequestered in the vacuole (Rauser, 1990).GSH is synthesized from glutamate, cysteine, and glycine by a two-step ATP-dependent reaction (Meister and Anderson, 1983). The first reaction forms ␥ -EC from glutamate and cysteine by the enzyme ␥ -EC synthetase (Hell and Bergmann, 1990), which is encoded by gsh1 (May and Leaver, 1995). GSH is then synthesized by the ligation of ␥ -EC and glycine in the reaction catalyzed by the enzyme GSH synthetase, which is encoded by gsh2 (Wang and Oliver, 1996). When GSH is oxidized as part of ...

Up-regulation of antioxidant and glyoxalase systems by exogenous glycinebetaine and proline in mung bean confer tolerance to cadmium stress

“…Furthermore, GSH plays a protective role in salt tolerance by maintaining the redox state (Shalata et al 2001). The increased level of the GSH pool is generally regarded as a protective response against oxidative stress (May and Leaver 1993;Xiang and Oliver 1998), although defense against stress situations sometimes occurs irrespective of the GSH concentration (Potters et al 2004). In this study, Cd stress caused a significant increase in GSH content (Fig.…”

“…2a). Increase in GSH content in response to Cd stress were also reported in rice seedlings (Hu et al 2009;Xu et al 2009) and GSH metabolic genes coordinately respond to heavy metal stress (Xiang and Oliver 1998). The increase in GSSG content under Cd stress in the seedlings may partly be attributed to a decreased rate of GSH recycling or an increased rate of its degradation under the conditions of stress Hossain and Fujita 2010).…”

Genetic engineering in the improvement of plants for phytoremediation of metal polluted soils

“…MT gene expression has been found to correlate with copper tolerance in A. thaliana (Murphy and Taiz, 1995). Recently, Xiang and Oliver (1998) showed increased transcription of the genes for glutathione synthesis, gglutamylcysteine synthetase and glutathione synthetase as well as glutahione reductase by Cd and Cu. Glutathione plays a pivotal role in protecting plants from Cu and Cd.…”

Heavy Metal Detoxification in Plants: Phytochelatin Biosynthesis and Function

“…) scriptional regulation in response to Cd exposure of genes involved in sulfur transport and assimilation and in GSH biosynthesis in Brassica juncea and in Arabidopsis. In Arabidopsis, the signal molecule, jasmonate, mediated an effect similar to Cd exposure (17 ). However, whether or not jasmonate is itself the signal in response to Cd has not yet been demonstrated.…”