Different approaches to improve the tolerance of aromatic and medicinal plants to salt stressed conditions

Salinity is a global environmental constraint that hinders the growth and development of various aromatic and medicinal plants (AMPs) and declines their yield and productivity. This is due mainly to the overaccumulation of salt ions in plant tissues, which affects negatively the physiology and cellular metabolic homeostasis. Recent investigations highlighted that the major functions driving plant growth and development and plant's survival such as seed germination, photosynthesis and water and mineral nutrition, are severely reduced in various AMPs under salinity constraint. Regarding their economic potential and their importance in worldwide health, improving the growth and production of AMPs, especially under salt-stressed conditions, is an important necessity and represents a global challenge. In this regard, seed priming and application of exogenous compounds have been reported among the most applied ecofriendly techniques to mitigate the effects of salt stress in various AMPs. Here, we first analyzed the harmful effects of salt stress on the growth and production of AMPs, by reporting the effects of salt ions on seed germination, flowering, photosynthesis, primary and secondary metabolite biosynthesis and essential oil production. This review also describes the potential effects of seed priming and exogenous compounds application in enhancing salt stress tolerance of several AMPs. Results and proposal mechanisms by which these approaches mitigate the negative effects of salinity on AMPs' growth and productivity are analyzed and critically discussed.