Elucidation of the role of glutathione reductase using transgenic plants

Abstract

The types of environmental stresses, both natural and anthropomorphic in origin, and physiological stresses that a plant is subjected to throughout its life are manifold. Examples are low temperatures combined with high light intensities, drought conditions, damage caused by pathogens, air-and waterborne pollutants and premature senescence [ 1,2].The physiological basis of the damage suffered by a plant during stress can often be explained as perturbations in oxygen metabolism leading to enhanced production of reactive oxygen intermediates (ROIs; hydrogen peroxide, superoxide anion and the hydroxyl radical). Most of the information available concerns the performance of photosynthesis in the leaf under stress [ 31. Disruption of the flow of energy from light-harvesting reactions, through electron-transport chains to CO, fixation, leads to 'leakage' of electrons to oxygen, causing the production of ROIs. If the protective mechanisms of the cell are compromised or overwhelmed, the effects on the plant are termed photooxidative damage. recognizing that during growth of the plant it is the chloroplast that is the primaryThe strategy of all aerobic organisms facing oxidative stress is to minimize production of KOls and to remove superoxide and hydrogen peroxide by reducing them to water by the concerted action of superoxide dismutases (S0I)s; EC 1.15.1 .l) and catalyses or peroxidases. In the chloroplast, the ~~ Abbreviations used: AI'X, ascorbate peroxidase; CaMV. cauliflower mosaic virus; GH, glutathione reductase; HOI. reactive oxygen intermediate: SO1 1, superoxide dis-$To whom correspondence should be addressed. 111utase.KOI-scavenging enzymes are Cu/%n-SOl)s (and sometimes Fe-SODS) [ 5 J and ascorbate peroxidase (APX; EC 1.11.1.7) [6J. The activities of these enzymes are supported by the antioxidants and enzymes of the glutathione-ascorbate cycle, which has been proposed to involve successive oxidations and reductions of ascorbate, glutathione and NADPI 1 by the enzymes APX. monodehydroascorbate reductase (EC 1.6.5.4), dehydroascorbate reductase (EC 1.8.5. I), glutathione reductase (GR; EC 1.6.4.2). Much of the information concerning this pathway has focused on its role in the prevention of photo-oxidative damage in the chloroplast, but the presence of enzymes of the glutathione-ascorbate cycle in non-photosynthetic tissues [7-9] demonstrates that this pathway may be functional in other cellular compartments. However, doubts about all, or part, of this cycle remain to be answered. In the chloroplast, an alternative route for the regeneration could be the direct reduction of monodehydroascorbate by electrons from photosystem I [ 101. The relative importance of glutathione-dependent versus glutathione-independent reactions for the regeneration of ascorbate and how the other roles of glutathione (see below) fit into this scheme have not been addressed.Our interest is to arrive at a more complete understanding of the roles of these enzymes in oxidative stress by applying molecular genetic techniques in conjunction wi...

A role for glutathione reductase and glutathione in the tolerance of Chlamydomonas reinhardtii to photo‐oxidative stress

“…This result is similar to the results obtained from transformation of GR localized in the cytosol (Foyer et al ) and is in contrast to the results obtained from the transformation of GR localized in the chloroplast in higher plants, i.e. that the glutathione pool size can be increased (Foyer et al , , Mullineaux et al ). Additionally, GR of bacterial origin can function in the chloroplasts of plant cells to increase both the GSH/GSSG ratio and the total glutathione pool (Noctor et al ).…”

Overexpression of Glutathione Reductase but Not Glutathione Synthetase Leads to Increases in Antioxidant Capacity and Resistance to Photoinhibition in Poplar Trees

“…Finally, GSH participates in many diverse cellular reactions; augmented levels may exert more indirect effects on protein synthesis and gene expression, which would contribute both to the observed decrease in susceptibility to photoinhibitory treatment and to the enhanced rates of recovery upon remova1 of the treatment. These results suggest that the high-chloroplastic-GR expressors are more robust as a result of the introduction of bacterial GR into the chloroplast, a conclusion in line with observations on other species transformed to express GR in the chloroplast (Aono et al, 1991(Aono et al, , 1993Mullineaux et al, 1994). This may prove to be of major ecological and practical significance and may have implications for improving methods of tree establishment.…”

“…This system may provide a means of studying the mechanisms that determine the level of GR activity in two discrete intracellular compartments. Recent work with N. tabacum (var Samsun) transformed with the GR cDNA from Pisum sativum (Creissen et al, 1991) has shown that overexpression of GR in the chloroplast, but not the cytosol, led to increases in the foliar GSH level by up to 50% (Mullineaux et al, 1994). In the present study, the foliar GSH level was also increased as a result of overexpression of bacterial GR in the chloroplast.…”

Glucose-6-phosphate dehydrogenase plays a central role in modulating reduced glutathione levels in reed callus under salt stress

“…The high-GSH pool maintained by GR in cells is necessary for active protein function and avoids unspecific formation of mixed disulfide bonds that cause protein inactivation or aggregation (Foyer and Noctor 2005b). Over-expression of the E. coli GR in chloroplast increased both total glutathione contents and GSH : GSSG ratio (Mullineaux et al 1994;Foyer et al 1995). GPX is the principle cellular enzyme capable of membrane lipid peroxidation repair and is generally considered to be the main line of enzymatic defense against oxidative membrane damage (Ursini et al 1995;Kühn and Borchert 2002).…”