Investigation of antioxidant enzymes activity and photosynthetic pigments content changes of stevia medicinal plant inoculated with Piriformospora indica fungi under salt stress

In order to evaluate the effect of Piriformospora indica fungi inoculation on antioxidant systems and photosynthetic pigments of Stevia under salt stress, an experiment was conducted in a factorial based completely randomized design with four replications under in vitro culture conditions. Factors include salinity at six levels (0, 50, 100, 150, 200 and 250 mM of NaCl) and inoculation of mycorrhizae like fungi at two levels (non-inoculated and inoculation with fungi). The results showed that the hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentration and catalase (CAT) activity was increased linearly in control plants while in inoculated plants fitted by a segmented equation. Accordingly, in mild stress the activity of these enzymes were reduced. Chlorophyll a, b and a content changed as a segmented model in both inoculated and uninoculated plants. Carotenoid content, however, linearly decreased in both inoculated (slope of -0.007) and uninoculated (slope of -0.005) plants. In conclusion, the results indicated that P. indica, particularly in low levels of salt stress, could reduce hydrogen peroxide (by two percent up to 124 mM of NaCl) and malondialdehyde content (17 percent up to 50 mM of NaCl) which resulted in decreased antioxidant activities and improved photosynthetic pigments and relatively increased tolerance to salt stress in stevia plants.