Exposed to salt stress, Salvia virgata Jacq. effects of elisitor application on physiological and antioxidant capacity

In this study, Salvia virgata plant was exposed to salt (NaCl) stress and zinc oxide nanoparticle (ZnONP), salicylic acid (SA) and ZnONP+SA combination was applied to plants divided into various groups. The photosynthetic pigment (chlorophyll a, chlorophyll b and carotenoids), proline (a stress-related amino acid), malondialdehyde (MDA, lipid peroxidation indicator), total phenolic and total flavonoid content of the plants were determined. Additionally, free radical scavenging activities such as DPPH, ABTS, and CUPRAC were measured to evaluate antioxidant capacity, and all the obtained data were evaluated comparatively. For this purpose, Salvia virgata plant was grown from seed and exposed to ¼ hoagland nutrient solution for 4 weeks and at the end of this period, other plants except the control group were exposed to 100 mM NaCl stress for 2 weeks. After a total of six weeks of growth, SA and ZnONP applications were made for 10 days on the potted plants. The pots were divided into five groups as follows: "Control, 100 mM NaCI, 100 mM NaCI + 500 μM SA, 100 mM NaCI + 20 mg/L ZnONP, and 100 mM NaCI + 500 μM SA + 20 mg/L ZnONP" and after the 10th day has been harvested. While salt stress application caused a decrease in chlorophyll a, chlorophyll b and carotenoid contents, SA, ZnONP, SA+ZnONP elicitors applied together with salt stress increased the content of all three pigments. Proline and MDA content increased as a result of salt stress application. Proline content increased more with elicitor applications, but MDA content decreased with elicitor applications compared to plants treated with only salt. The lowest amount of proline in the control group (2.293±0.13 mM g-1), the highest amount of proline in NaCl+SA+ZnONP (4.128±0.18 mM g-1) application; the lowest MDA content was found in the control group (1.674±0.09 µM g-1), and the highest MDA content was determined in NaCl (3.666±0.11 µM g-1) application. The application of salt stress and the combined application of SA, ZnONP, and SA+ZnONP increased the total phenolic and total flavonoid content compared to the control group. Moreover, it was observed that elicitor applications resulted in a greater increase in total phenolic and flavonoid content than salt stress alone. The lowest total phenolic content (166.82± 1.72 μg) and total flavonoid content (62.25± 0.78 μg) in the control group; the highest total phenolic content (314.96±3.47 μg) and total flavonoid content (114.50±1.96 μg) in the NaCl+ZnONP treatment group were observed. The results obtained from the DPPH, ABTS, and CUPRAC methods, used to determine total antioxidant activity, showed similarities. Salt stress and all elicitor applications with salt increased antioxidant activity compared to the control group. The antioxidant activity of the three methods were similar and the activity sorting from largest to smallest was determined as NaCI+ZnONP > NaCI+SA > NaCI+SA+ZnONP > NaCI > Control. In addition, it was observed that the activity values obtained from the SA, ZnONP, and SA+ZnONP applications in the DPPH method exhibited higher antioxidant activity than the positive control BHT, while in the ABTS and CUPRAC methods, the NaCl+ZnONP application showed higher antioxidant activity than the positive control BHA. According to the obtained results, it can be concluded that the NaCI+SA+ZnONP elicitor application is more effective in terms of photosynthetic pigment, proline, and MDA content, while the NaCI+ZnONP elicitor application is more effective in terms of total phenolic and total flavonoid content, as well as total antioxidant activity. Additionally, when evaluating the effects of SA and ZnONP on reducing stress damage and secondary metabolite (phenolic, flavonoid, carotenoid) production together, it was observed that SA and ZnONP exhibit a synergistic effect, especially in reducing stress damage. SA and ZnONP applications may have the potential to reduce the effects of stress in plants under salt stress. However, it should be noted that these effects may vary depending on the plant species, stress conditions, application methods and concentrations of elicitors used. Therefore, further research on the use of elicitors such as SA and ZnONP in stress management strategies is recommended. Such research can help us better understand the effectiveness and application protocols of these elicitors and develop strategies that support better adaptation of plants to environmental stresses like salt stress.