Melatonin mitigates adverse effects of salinity in stevia through physiological and biochemical adjustments

Stevia is a valuable medicinal plant known for its abundance of sterols, phytochemicals, natural antioxidants, and glycosides-stevioside. Its traditional use extends to the regulation of blood pressure and diabetes. However, the production of stevia faces challenges due to various abiotic stresses, with salinity being a prominent constraint affecting its sustainable productivity. In light of this, the current study was designed to assess the impact of melatonin (MEL) (100 mu M) on stevia plants growing under normal and saline conditions (0, 40, 80 and 120 mM NaCl). The findings of this study highlight the significant effect of MEL sprays on stevia growth and yield under saline conditions. MEL supplementation significantly played a crucial role in regulating photosynthetic pigments, net photosynthesis, and stomatal conductance, effectively mitigating the adverse effect of different salinity levels. MEL improved plant defense system by reducing oxidative stress activities such as H2O2 and MDA, which are known indicators of cellular damage caused by salinity stress. Importantly, MEL supplementation also played a significant role in regulating the uptake of sodium (Na+) and potassium (K+) in stevia plants under saline conditions. This regulation of ion uptake helps maintain ion homeostasis and prevents ion toxicity, thus contributing to the overall improvement of stevia plant health and productivity in saline environments. Overall, the results of this study provide valuable insights into the effectiveness of MEL in promoting sustainable stevia production under saline conditions.