Physiological and Molecular Responses of Lotus to Chilling Stress: Roles of ROS Signaling and Antioxidant Systems

Lotus (Nelumbo nucifera Gaertn.) is an economically important aquatic plant valued for its ornamental, nutritional, and medicinal properties however, its productivity is significantly constrained by chilling stress. Low-temperature exposure disrupts cellular metabolism and induces excessive accumulation of reactive oxygen species (ROS), leading to oxidative damage to lipids, proteins, and nucleic acids. To mitigate these effects, lotus activates complex physiological, biochemical, and molecular defense mechanisms, primarily involving antioxidant systems and stress-responsive gene regulation. This review summarizes current knowledge on ROS signaling and antioxidant defense in lotus under chilling stress, with emphasis on enzymatic antioxidants such as superoxide dismutase, catalase, peroxidases, and peroxiredoxins, as well as key genes including NnMSD1, NnCAT, and NnPER1. It also highlights the role of cold acclimation in enhancing stress tolerance through osmotic adjustment, metabolic reprogramming, and transcriptional regulation involving Q-type C2H2 zinc finger proteins and MAPK signaling cascades. Furthermore, the crosstalk between ROS signaling and phytohormones such as abscisic acid, jasmonic acid, auxin, ethylene, and salicylic acid is discussed in relation to stress adaptation and postharvest physiology. Recent genomic and functional studies indicate that coordinated regulation of antioxidant defense and signaling networks is essential for maintaining redox homeostasis and improving stress resilience. The review also considers postharvest treatments, including melatonin, 1-methylcyclopropene, and lacquer wax, which enhance antioxidant capacity and reduce oxidative damage. Overall, understanding ROS-mediated signaling and antioxidant regulation provides valuable insights into chilling tolerance mechanisms in lotus and offers potential targets for developing stress-resilient cultivars.