Scanning electron microscopy, biochemical and enzymatic studies to evaluate hydro-priming and cold plasma treatment effects on the germination of Salvia leriifolia Benth. seeds

Finding a suitable method to increase seed germination rates of medicinal plants is critical to saving them from extinction. The effects of cold plasma (CP) treatments (using surface power densities of 80 and 100 W, with exposure times of 0, 120, 180, and 240 s) and incorporating hydropriming (carried out for 24 and 2 h on normal and uncovered seeds, respectively) to enhance the seed germination of Salvia leriifolia Benth a native endangered Iranian medicinal plant, were evaluated in this study. Scanning electron microscopy (SEM) images identified more destroyed mesh-like structures in hydro-primed and uncovered seeds than in normal and dry seeds. In comparison to the control, and other treatments, employing 100 W of CP for 240 s produced the maximum germination percentage and rate, as well as a seedling vigor of I and II in hydro-primed and uncovered seeds. The levels of alpha-amylase activity increased when the power and exposure times of CP were increased. The uncovering and hydropriming of S. leriifolia seeds resulted in increased enzyme activity. Malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents were enhanced by increasing the power and exposure time of CP, especially in uncovered and hydro-primed seeds. The activity of antioxidant enzymes, including catalase (CAT) and superoxide dismutase (SOD), was correlated to changes in MDA and H2O2 levels. Finally, direct contact of CP with uncovered seeds in a short exposure time can improve the germination of S. leriifolia seeds via microscopic etching and activation of enzymes.