Cell-type-specific H+-ATPase activity and antioxidant enzymes improve the Echinacea purpurea L. Moench tolerance to salinity stress at different NO3-/NH4+ ratios

While the importance of biochemical processes in plant adaptive responses is widely accepted, only a limited number of studies have addressed cell-type specific and enzymatic activities in E. purpurea under salt stress conditions. So, various antioxidant enzymatic activities, H+ transport activity, and non-invasive ion flux mechanisms in the root apex and mature zones of E. purpurea grown at different NO3-/NH4+ ratios (90:10, 80:20, and 70:30) were studied in salinity stress condition (0, 15, 30, and 60 mM NaCl). Various parameters, photosynthetic and transpiration rates, gas exchange, ion accumulation, electrolyte leakage (EL) in addition to antioxidant enzyme activities and cell-specific mechanisms were measured according to the standard methods. Based on the results, 60 mM NaCl salinity stress significantly decomposed the cell membrane, causing to increase in the electrolyte leakage and malondialdehyde (MDA) content (89.4% compared with control) and a decrease in the photosynthetic rate (84% compared with control). The activity of antioxidant enzymes such as superoxide dismutase (SOD) and ascorbate peroxidase (APX), catalase (CAT), and glutathione peroxidase (GP) significantly increased up to 30 mM NaCl to diminish the free radicals content by increasing the hydrogen peroxide (H2O2) concentration (89.4% compared with control). High Na+ and Cl- content and their accumulation in the leaves caused to inhibit the antioxidants enzymes activities at 60 mM NaCl salinity stress. Based on the nitrogen (N) supply form, more antioxidant activities and physiological properties were found at the 90:10 NO3-/NH4+ ratio. Salinity stress is caused to limit the root apex growth in a high tissue- and treatment-specific manner. The differential sensitivity between the two zones originates from a 10-fold difference in K+ efflux and H+-ATPase activity between the mature zone and the apical region.