Melatonin Inhibited Cadmium Accumulation and Protected Plant Photosynthetic Machinery in Eggplant Seedlings

Abstract

Cadmium (Cd) is one of the most injurious heavy metals, affecting plant growth and development. Melatonin (MEL), as a plant growth regulator, has been used to alleviate Cd toxicity in many plant species; however, the underlying molecular mechanisms responsible for Cd toxicity in eggplant are still poorly understood. Our results showed that MEL (100 mM), led to positive effects on Cd tolerance, including a significant increase in growth, photosynthetic pigments, and proline content. Exogenous MEL could improve photosynthetic assimilation rate in Cd-treated plants, probably through an increase in proline. Further, MEL led to a decrease in Cd translocation to the shoots. Based on the results, MEL considerably increased antioxidant enzymes (SOD, POD, CAT, APX, GR, GST) activities as well as the production of anthocyanin, total phenols, and flavonoids. The increased activity of antioxidant enzymes led to a decrease in electrolyte leakage (EL), malonaldehyde (MDA), superoxide ion (O₂^•−) and hydrogen peroxide (H₂O₂) content in the plants exposed to Cd stress. Furthermore, MEL application efficiently increased the mineral nutrient accumulation in plants. In conclusion, the results showed that the use of MEL could reduce oxidative stress and improve biomass in the plants exposed to Cd. These results may be used to develop novel techniques for enhancing agricultural yield sustainably, especially in metal-contaminated soils.