Salt tolerance mechanisms in five Asteraceae species: seed germination and seedling growth, cellular damage, enzymatic and non-enzymatic antioxidants

Exploring the saline-adapted species and the mechanisms by which they have evolved in saline conditions would be a feasible way to utilize saline soils. Based on this approach, this study aimed to evaluate the seed germination and seedling responses of the five abundant Asteraceae species to salinity stress and determine the antioxidant and non-antioxidant defense strategies by which these species demonstrated variations in salinity tolerance. Milk thistle (Silybum marianum), blessed thistle (Cnicus benedictus), pot marigold (Calendula officinalis), safflower (Carthamus tinctorius), and cardoon (Cynara cardunculus) were subjected to 0 (control), 50, 100, 150, 200 and 250 Mm NaCl concentrations. Calendula officinalis (CO) showed the highest, Silybum marianum (SM) and Cnicus benedictus (CB) moderate, and Carthamus tinctorius (CT) followed by Cynara cardunculus (CC) the least inhibition of seed germination and seedling growth at all given salinity levels. Each species utilized different antioxidant mechanisms in response to salinity. Peroxidase (POX) was the major antioxidative enzyme in resistance species, CT and CC, while catalase and superoxide dismutase were more pronounced in moderate, SM and CB, and susceptible, CO, species, respectively. Besides, all species accumulate a considerable amount of proline in response to salinity, which was more evident in the 150 and 200 Mm NaCl concentrations. From the results, it can be concluded that CT and CC had superior saline-tolerance capacity compared to other species due to their longer seedling roots, higher POX activity, and proline accumulation associated with reduced cellular damage.