Exogenous melatonin enhances salt stress tolerance in tomato seedlings

Melatonin (N-acetyl-5-methoxytryptamine) is an essential molecule which regulates plant growth and development and alleviates the damaging effects of abiotic stresses. To evaluate the important functions of melatonin in response to salinity stress, the effects of exogenous melatonin on the antioxidant system and growth of tomato (Solanum lycopersicum L.) under 150 mM NaCl stress were investigated. The application of 100 mu M melatonin compensated the growth inhibition caused by salt-stress. Melatonin treated seedlings had an increased fresh and dry masses of shoots and roots. The application of 1 200 mu M melatonin notably enhanced the relative chlorophyll content (SPAD index), root characteristics, and gas exchange in tomato seedlings subjected to salt stress compared to seedlings treated with salt stress alone. Moreover, melatonin pretreatment minimized accumulation of reactive oxygen species and improved activities of antioxidative enzymes including catalase, superoxide dismutase, glutathione reductase, and ascorbate peroxidase.