Elucidating effect of ZnO-Nanoparticles and melatonin on physiological adjustments and growth of Solanum melongena under salinity stress

Abiotic stress is a major constraint to the successful growth and development of vegetables. Melatonin (MT) is a tryptophan derivative, a multipurpose phytochemical that ameliorates the adversity of abiotic stress on plants. In this study, Zinc oxide nanoparticles (ZnO-NPs) and melatonin were applied to Solanum melongena (Brinjal) cultivated in a salinity-stressed environment to effectively reduce the harmful effect of salt stress. Seeds of S. melongena were grown in plastic pots and exposed to various treatments, including control and seed priming with ZnO-NPs1, ZnO-NPs2, and ZnO-NPs3 for 25 days at concentrations of 50 mM, 100 mM, 200 mM and, 200 mM MT. In a seed primed with 60mg/L ZnO-NPs and a 100 mM salt solution, the maximum shoot length was 16.3 cm. Under 100 mM salt solution, concentrations of chlorophyll a and b in 80 mg/L ZnO-NPs and 200 mM MT primed seed grew dramatically to 0.42, 0.49, 0.50, and 0.57 mg/g respectively. Under 50 mM of salt solution, 40 mg/L of ZnO-NP-primed seeds dramatically increased total chlorophyll contents to 1.12 mg/g. In 200 mM MT primed seed, the content of carotenoids dramatically increased to 3.3 mg/g. Nanoparticles and MT-induced growth of Brinjal, especially under conditions of salt stress, were found to be related to higher levels of photosynthetic pigments, total soluble sugars, total soluble proteins, and total free amino acids. Therefore, it is concluded that exogenous melatonin along with Zinc oxide nanoparticle treatment useful for enhancing plants' ability to survive undunder salt stress.