Sphaerophysa kotschyana, an endemic species from Central Anatolia: antioxidant system responses under salt stress

Sphaerophysa kotschyana is a Turkish endemic and endangered plant that grows near Salt Lake, in Konya, Turkey. However, little is known about the ability of this plant to generate/remove reactive oxygen species (ROS) or its adaptive biochemical responses to saline environments. After exposure of S. kotschyana to 0, 150, and 300 mM NaCl for 7 and 14 days, we investigated (1) the activities and isozyme compositions of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), and glutathione reductase (GR); (2) the oxidative stress parameters NADPH oxidase (NOX) activity, lipid peroxidation (MDA), total ascorbate (tAsA) content, and total glutathione content (tGlut); and (3) ROS levels for superoxide anion radical (O 2 (·-) ), hydrogen peroxide (H2O2), hydroxyl radicals (OH·), and histochemical staining of O 2 (·-) and H2O2. H2O2 content increased after 14 days of salt stress, which was consistent with the results from histochemical staining and NOX activity measurements. In contrast, oxidative stress induced by 150 mM NaCl was more efficiently prevented, as indicated by low malondialdehyde (MDA) levels and especially at 7 days, by increased levels of SOD, POX, APX, and GR. However, at 300 mM NaCl, decreased levels of protective enzymes such as SOD, CAT, POX, and GR, particularly with long-term stress (14 days), resulted in limited ROS scavenging activity and increased MDA levels. Moreover, at 300 mM NaCl, the high H2O2 content caused oxidative damage rather than inducing protective responses against H2O2. These results suggest that S. kotschyana is potentially tolerant to salt-induced damage only at low salt concentrations.