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

Abstract

A poplar hybrid, Populus tremula x Populus alba, was transformed with the bacterial genes for either glutathione reductase (CR) (gor) or glutathione synthetase (CS) (gshln. When thegorgene was targeted to the chloroplasts, leaf CR activities were up to 1000 times greater than in all other lines. In contrast, targeting to the cytosol resulted in 2 to 10 times the CR activity. CR mRNA, protein, and activity levels suggest that bacterial CR is more stable in the chloroplast. When the gshll gene was expressed in the cytosol, CS activities were up to 100 times greater than in other lines. Overexpression of CR or CS in the cytosol had no effect on glutathione levels, but chloroplastic-GR expression caused a doubling of leaf glutathione and an increase in reduction state. The high-chloroplastic-CR expressors showed increased resistance to photoinhibition. The herbicide methyl viologen inhibited COz assimilation in alllines, but the increased leaf levels of glutathione and ascorbate in the high-chloroplastic-CR expressors persisted despite this treatment. These results suggest that overexpression of GR in the chloroplast increases the antioxidant capacity of the leaves and that this improves the capacity to withstand oxidative stress.

Modification of reactive oxygen species scavenging capacity of chloroplasts through plastid transformation

“…We found that elevation of plastid GR activity over-rides feedback control of glutathione synthesis leading to elevated total glutathione levels. Broadbent et al (1995) and Foyer et al (1995) report a similar finding in nuclear transformants of tobacco and poplar respectively.…”

“…However, our finding matches that of Creissen et al (1999) who increased GSH levels by transformation with a gene for a chloroplast-targeted c-glutamylcysteine synthetase (c-ECS) and found increased oxidative stress, which they explained on the basis of impaired redox sensing in the chloroplast. We contend that the increased MV sensitivity of the transplastomic lines over-expressing GR has a similar basis, although it is not reflected in a study in poplar (Foyer et al 1995) in which chloroplast targeted GR did result in improved oxidative stress tolerance. Another study with tobacco (Broadbent et al 1995) showed considerable interline variation, some GR over-expressing lines giving a modest increase in oxidative stress tolerance, while others did not.…”

“…Catalase over-expression in tobacco resulted in enhanced recovery from high light intensity and MV (Miyagawa et al 2000), while expression of an ascorbate peroxidase gene resulted in protection against aminotriazole (but not paraquat)-induced oxidative stress (Wang et al 1999) and heat stress (Shi et al 2001) in Arabidopsis, and salt and drought stress in tobacco (Badawi et al 2004a). A similar outcome was achieved through the overexpression of glutathione reductase in tobacco (Aono et al 1993) and poplar (Foyer et al 1995). Some investigators have extended the transgenic approach to explore simultaneous over-expression of more than one enzyme associated with ROS scavenging.…”

Comparison of an antioxidant system in tolerant and susceptible wheat seedlings in response to salt stress

“…Several genes encoding for plant antioxidant enzymes have been cloned, characterized, and used in the construction of transgenic lines. Transgenic plants overexpressing SOD (Bowler et al, 1991;Van Camp et al, 1996;Breusegem et al, 1999;Alscher et al, 2002;Feki et al, 2016), APX (Wang et al, 1999), GR (Foyer et al, 1995), GPX (Roxas et al, 1997(Roxas et al, , 2000 and CAT (Feki et al, 2015) showed tolerance to various abiotic stresses.…”

Induction of Oxidative Stress by Sunflower Phytotoxins in Germinating Mustard Seeds

“…Synthesis of SOD and CAT as an adaptive response to oxidative stress has been reviewed (Mittler, 2002). In addition, effective resistance to prolonged stress would necessitate an augmented capacity for ascorbate regeneration, a process at least partly dependent on the tripeptide thiol (glutathione) in higher plants (Foyer et al, 1995). An important role in glutathione oxidation to glutathione disulfate is played by the latter enzyme in the ascorbate-glutathione cycle, glutathione reductase (GR).…”