The dehydrogenase‐mediated recycling of NADPH is a key antioxidant system against salt‐induced oxidative stress in olive plants

Abstract

NADPH is an important molecule in the redox balance of the cell. In this paper, using olive tissue cultures as a model of the function of the NADPH-generating dehydrogenases in the mechanism of oxidative stress induced by severe salinity conditions was studied. When olive ( Olea europaea ) plants were grown with 200 m M NaCl, a 40% reduction in leaf fresh weight was produced. The content of nonenzymatic antioxidants such as ascorbate and glutathione was diminished between 20% to 39%, whereas the H 2 O 2 content was increased threefold. In contrast, the analysis of the activity and protein contents of the main antioxidative enzymes showed a significant increase of catalase, superoxide dismutase and glutathione reductase. Overall, these changes strongly suggests that NaCl induces oxidative stress in olive plants. On the other hand, while the content of glucose-6-phosphate was increased almost eightfold in leaves of plants grown under salt stress, the content of NAD(P)H (reduced and oxided forms) did not show significant variations. Under salt stress conditions, the activity and protein contents of the main NADPH-recycling enzymes, glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (ICDH), malic enzyme (ME) and ferrodoxin-NADP reductase (FNR) showed an enhancement of 30-50%. In leaves of olive plants grown with 200 m M NaCl, analysis of G6PDH by immunocytochemistry and confocal laser scanning microscopy showed a general increase of this protein in epidermis, palisade and spongy mesophyll cells. These results indicate that in olive plants, salinity causes reactive oxygen species (ROS)-mediated oxidative stress, and plants respond to this situation by inducing different antioxidative enzymes, especially the NADPH-producing dehydrogenases in order to recycle NADPH necessary for the protection against oxidative damages. These NADP-dehydrogenases appear to be key antioxidative enzymes in olive plants under salt stress conditions.

Stress-Induced GSK3 Regulates the Redox Stress Response by Phosphorylating Glucose-6-Phosphate Dehydrogenase in Arabidopsis

“…The activity of G6PD, a key enzyme of the OPPP, increased in Arabidopsis plants upon high salinity stress. Consistently, G6PD activity was reported to be induced by NaCl treatment in other plant species (Valderrama et al, 2006;Wang et al, 2008). Importantly, loss of G6PD6 impinged on the redox status of glutathione and rendered plants more sensitive to salt stress.…”

“…In plants, G6PD activity is present in the plastids and cytosol (Debnam and Emes, 1999). G6PD activity has been positively correlated with environmental stresses such as salt stress (Valderrama et al, 2006;Wang et al, 2008), aluminum toxicity (Slaski et al, 2006), drought (Scharte et al, 2009), and infection by viral and fungal pathogens (Sindelár and Sindelárová, 2002;Scharte et al, 2009); by contrast, a decrease in chloroplastic G6PD activity has been shown to be beneficial for withstanding oxidative stress (Debnam et al, 2004). Thus, the role of G6PD in the stress response is currently unclear.…”

“…Membranes were probed with a 1:5000 dilution of anti-ASKa, anti-Myc (Santa-Cruz), or anti-HA (Santa-Cruz) antibodies. To detect total G6PD protein levels, a 1:6000 dilution of polyclonal antibody against Saccharomyces cerevisiae G6PD (Sigma-Aldrich) was used as described for plants (Valderrama et al, 2006). Alkaline phosphatase-conjugated goat anti-rabbit IgG (Santa-Cruz) was used as the secondary antibody.…”

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…Proteins that function to reduce NAD(P) to NAD(P)H or alter the level of ATP were found to be essential for plant tolerance to oxidative stress (Chai et al, 2006;Valderrama et al, 2006;Marino et al, 2007;Noctor et al, 2007;Rodriguez et al, 2007;Vidal et al, 2007). These reports strengthen the link between ROS scavenging and metabolism and demonstrate that proper regulation of ROS requires reducing power that can be supplied by photosynthesis, respiration, and/or different carbon utilization pathways.…”

Salt-Induced Changes in Antioxidative Enzyme Activities in Shoot Tissues of Two Atriplex Varieties

“…The ROS concentration in the tissues directly exposed to salt are strongly influenced by the coordinated action of different antioxidative enzymes (Munns and Tester, 2008). Recently, it has been reported that salinity provoked in plant leaves an imbalance between ROS production and antioxidant defenses, with the induction of oxidative stress (Valderrama et al, 2006). To counteract the toxicity of ROS, defense systems that scavenge cellular ROS have been developed in plants to cope with oxidative stress via the nonenzymatic and enzymatic systems (Noctor and Foyer, 1998).…”