Melatonin-mediated nitric oxide signaling enhances adaptation of tomato plants to aluminum stress

Recently, the significance of the interplay between nitric oxide (NO) and melatonin (ML) in the defense responses of plants against abiotic stresses has gained considerable attention. However, the impact of this relationship on plant adaptation to aluminum (Al) contamination is yet to be determined. The current study investigated the relationship between the application of external ML (150 mM) and internal NO on the defense mechanisms of tomato plants during Al (148 mM) stress. Applying Al stress resulted in elevated lev -els of malondialdehyde, electrolyte leakage, superoxide anion, hydrogen peroxide, and Al concentration in the roots and leaves. These increases were accompanied by a decline in growth, biomass, and photosynthetic pigments. The addition of ML to the roots of tomatoes experiencing Al contamination resulted in enhanced activity of antioxidant enzymes, which protected the cell membranes and photosynthetic pigments against AL toxicity by lowering the internal level of ROS. ML treatment increased quantities of phytochelatins, gluta-thione, and NO in the leaves and roots of plants under Al contamination. This increase in thiol compounds and NO contributed to the reduction of Al translocation to the leaves by promoting the immobilization mech-anism of Al in the roots. However, when ML-exposed plants were subjected to a NO scavenger, carboxy-PTIO, the protective impacts of ML were suppressed. This indicates the involvement of NO in the induced defense responses by ML. Thus, our findings demonstrate that ML facilitates the adaptation of tomato seedlings under Al stress by regulating internal NO.(c) 2023 SAAB. Published by Elsevier B.V. All rights reserved.