Responses of ajowan (Trachyspermum ammi L.) to exogenous salicylic acid and iron oxide nanoparticles under salt stress

This research with a factorial arrangement was undertaken to investigate physiological responses of ajowan plants to foliar treatment of salicylic acid (1 mM) and nano-Fe2O3 (3 mM) under various salinity levels (0, 4, 8, 12 dS m−1 NaCl, respectively). Rising salinity enhanced sodium and endogenous SA contents, soluble sugars, protein, glycine betaine, proline, antioxidant enzymes activities, ROS generation, and lipid peroxidation, while reduced potassium and iron contents, membrane stability index, leaf water content, leaf pigments, root and shoot biomasses, and seed yield. Application of particularly SA and SA+nano-Fe2O3 alleviated salt toxicity via enhancing K+ uptake, K+/Na+ ratio, Fe content, endogenous level of SA, the activities of antioxidant enzymes (superoxide dismutase, catalase, peroxidase, and polyphenol oxidase), and most of the osmolytes. These changes were resulted in improving membrane stability index, leaf water content, leaf pigments, root and shoot growth, and finally seed yield of plants under moderate and severe salinities. Therefore, these treatments can additively enhance salt tolerance and physiological performance of ajowan through increasing antioxidant capacity, osmolytes, and photosynthetic pigments.