Deciphering the molecular mechanisms of leaf senescence: from nutrient remobilization to stress tolerance improvement

Leaf senescence is a natural phenomenon observed in plants, representing the final stage of leaf development, which is a strictly regulated process. It is a strategy for plants to optimize the nutrient utilization and enhance survival under changing environments. In aging leaves, the degradation of numerous macromolecules provides additional sources of nutrients by transporting metabolites to young tissues or storage organs, especially in seeds of annual crops. Both internal and external factors can influence senescence including aging, phytohormones, nutrient limitation, extreme temperatures, drought, high salinity, shading, and pathogen attack. This review generalized the influence of phytohormones on leaf aging and regulatory pathways involved in stress-induced leaf senescence. Reactive oxygen species (ROS) play an important role in programmed cell death, the final stage of leaf senescence. Therefore, the functions of ROS in the regulation of leaf senescence in Arabidopsis, representative crop plants and leafy vegetables are also summarized. Lastly, we discussed and prospected the application of leaf senescence mechanism in agricultural production in terms of ripening control and stress tolerance improvement. The precise timing and initiation of leaf senescence are of great significance for crop yield, vegetable preservation, and adversity adaptation.