Melatonin Alleviates Oxidative Damage of Photosynthesis Under Heat Stress in Tomato

Melatonin ( N -acetyl-5-methoxytryptamine) is a pleiotropic signaling molecule first found in animals which has multiple functions in plant resistance to abiotic stress. To elucidate how is melatonin (MT) affects the photosynthesis of tomatoes under heat stress. In this study, 50 μmol·L -1 MT pretreatment followed by exposure to heat stress for 7 days. Under heat stress, chlorophyll content and carbon assimilation were decreased in tomato seedlings; The ability of photosystem II (PSII) was hurt by light capture and utilize reduction; The number of active reaction centers was decreased, as well as the proportion of absorbed light used for electron transfer in varying degrees; The activity both of oxygen-evolving complex (OEC) on PSII electron donor side and electrons transfer process of Q A to Q B on PSII electron receptor side was blocked; PSII core proteins were degraded with reactive oxygen species (ROS) bursting. Oxidative damage is one of the main factors which limit the photosynthetic efficiency under heat stress. Exogenous MT significantly mitigated photosynthetic systems limited by heat stress. In particular, melatonin alleviated the oxidative damage of PSII by balancing the electron transfer of the donor side, reaction center, and receptor side. Further, redox proteomics suggested that phosphorylated and redox proteins of heat resistant signaling pathway were regulated by melatonin which increases the expression of oxidative genes in downstream. The abundance of antioxidant enzymes were alleviated to maintain their activity and ROS homeostasis by melatonin in heat stress. The revelation of redox proteins that responded to heat stress provided a basis for tomato breeding. The positive roles of MT enhanced scientific regulation of crop growth and increased crop yield