Melatonin promotes the normal cellular mitochondrial function of lotus seeds through stimulating nitric oxide production

• Melatonin treatment induced endogenous nitric oxide production of lotus seeds. • Postharvest browning of lotus seeds was accelerated by nitric oxide scavenger. • Melatonin alleviated mitochondrial oxidative damage and ATP loss in lotus seeds. • Melatonin maintained normal cellular mitochondrial functioning of lotus seeds. Melatonin (MT) plays a vital role in diverse physiological processes of postharvest fruit and vegetables but information on the involvement of nitric oxide (NO) in the MT pathway is limited. The effect of NO, MT and MT combined with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (MT + cPTIO) on the cellular mitochondrial function of lotus seeds was investigated. The browning of lotus seeds was delayed by NO and MT treatments but aggravated by cPTIO treatment. Reactive oxygen species in the mitochondria of NO and MT-treated seeds were efficiently scavenged by antioxidant enzymes stimulated by the treatment, thus inhibiting malondialdehyde production and oxidative damage of the mitochondria. The activities of energy metabolism-related enzymes involved in the respiratory chain were also increased by NO and MT treatments, thereby enhancing ATP production in the lotus seeds. This resulted in increased mitochondrial membrane potential and oxygen consumption during respiratory metabolism. However, the MT + cPTIO treatment produced the opposite effect to MT alone that increased NOS activity but showed no consistent effect on NR activity. These findings suggested that exogenous MT treatment maintained normal mitochondrial function in lotus seeds by inducing endogenous NO production, which could be resulted from the increased NOS activity.