Physiochemical and molecular responses of salt-stressed lemon balm (Melissa officinalis L.) to exogenous protectants

Worldwide, salt stress is one the major limiting factors of crop production particularly in arid and semi-arid areas. Here, responses of salt-stressed lemon balm (Melissa officinalis L.) to exogenously applied protective substances including reduced glutathione (GSH), proline and salicylic acid were studied to elucidate the regulatory roles of these protectants at the physiochemical and molecular levels. Under salinity, supplying exogenous protectants improved the contents of photosynthetic pigments and proline, triggered accumulation of phenolic compounds and expression of related biosynthetic genes, enhanced antioxidant capacity and modulated stress-induced lipid peroxidation which indicate the regulatory functions of applied protectants in lemon balm plant in this condition. In addition, there were strong correlations between the expression levels of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) genes, as key components of the phenylpropanoid pathway and the contents of total phenolics and flavonoids. In this study, a partial-length of lemon balm CHS gene was also cloned and sequenced for the first time.