The induction of salt stress tolerance by jasmonic acid treatment in roselle (Hibiscus sabdariffa L.) seedlings through enhancing antioxidant enzymes activity and metabolic changes

The objective of the present study was to assess the effects of exogenous application of 1 mM Jasmonic acid (JA), an endogenous plant growth regulator, on mitigation of oxidative and osmotic stresses caused by various levels of NaCl: none (0 mM), light (50 mM), moderate (150 mM), and severe (300 mM) in roselle (Hibiscus sabdariffa L.) seedlings. Salt stress without any change in leaf water content negatively affected seedlings growth from the aspect of plant height, root length, leaf morphological properties, plant biomass and levels of pigments, reducing sugars, starch, proteins and free amino acids, but accumulated higher levels of non-reducing sugars, total phenols, anthocyanins, flavonoids, proline and increased activities of both enzymatic and non-enzymatic antioxidants, such as ascorbate peroxidase (APX), pyrogallol peroxidase (PPX) and polyphenol oxidase (PPO). JA-treated seedlings exhibited a significant increase in growth parameters and activities of APX and PPX under salt stress, with hyper-accumulation of metabolite levels, but accumulated lower amounts of dry matter in roots and decreased the activity of PPO. These results clearly showed that exogenous JA treatment protected roselle seedlings against salt-induced damage through up-regulating the activity of H2O2-decomposing enzymes, osmoprotectants biosynthesis, and the accumulation of metabolites.