Enhancement of salt tolerance in quinoa (Chenopodium quinoa var. Titicaca) by seed priming with melatonin

In plants, melatonin (N-acetyl-5-methoxytryptamine) contributes to various environmental stress responses and developmental processes. Accordingly, the effect of seed priming with melatonin (1250 µM) on increasing salt tolerance at 40 dS m-1 NaCl was studied in Chenopodium quinoa var. Titicaca (quinoa) using a factorial experiment based on a completely randomized design at Shahrekord University in 2019. In the present experiment, different levels of NaCl and melatonin were first applied and according to the obtained results, 1250 μM melatonin and 40 dS m-1 NaCl were selected for the main study. The measured traits and indices included the fresh and dry weight, the content of photosynthetic pigments, hydrogen peroxide (H2O2), malondialdehyde (MDA), as well as the activity of catalase, ascorbate peroxidase, and guaiacol peroxidase. Seed priming with melatonin reduced the adverse effects of NaCl in the salt-stressed quinoa plants by increasing the dry weight (two-fold) and the level of photosynthetic pigments (1.2-fold) compared to the salinity stress alone. Also, the application of melatonin by changing the activity of antioxidant enzymes, reduced the content of H2O2 by 25% and MDA by 42%, which resulted in the reduction of oxidative stress in the quinoa plants under salinity conditions. Overall, it can be concluded that seed priming with an optimal level of melatonin can be a proper technique to increase salt tolerance in quinoa under highly saline conditions by reducing the harmful effects of salinity-induced oxidative stress by reducing the H2O2 and lipid peroxidation levels. It also protects the photosynthetic machinery by reducing the degradation of photosynthetic pigments which leads to the increased growth of the quinoa plants under salinity conditions.