The Roles of Selenium in Protecting Lemon Balm against Salt Stress

Plant metabolism and productivity is influenced adversely by salinity. Exogenous selenium (Se), applied as sodium selenate in biofortification programmes, has been found effective in alleviating the salt induced damage in plants. The study was conducted in order to determine the effects of exogenous Se supply (10 μM) on the resistance of lemon balm (Melissa officinalis L.) plants to salt stress (40 mM NaCl). Plant growth was negatively affected by salinity and dry mass production as well as chlorophyll a and b accumulation severely reduced. Selenium significantly improved the growth rate and increased the photosynthetic pigments and total amino acid contents in lemon balm plants subjected to salt stress. Salinity stress caused great membrane damage, as assessed by lipid peroxidation, but Se application significantly reduced the membrane damage because of an efficient scavenging by peroxidases (POD) and glutathione peroxidase (GSH-Px). Compared with the non-selenium treatment, application of Se increased the activity of phenylalanine ammonia-lyase (PAL) under salinity. As a result, the physiological and biochemical parameters measured in this study indicated that the salinity had adverse effects on growth of lemon balm plants, but the data also showed that presence of exogenous Se in nutrient solution could alleviate seedling damage under high levels of NaCl in the medium.