The role of cytokinins during flooding stress in plants

In a world where climate change is increasingly affecting crop production, research into the functions of phytohormones during environmental stresses is crucial for the development of resilient crops. Cytokinins (CKs), conventionally recognized for their roles in cell division and vascular development, also exhibit involvement in stress adaptation. In the current climate setting, flooding events are increasing in both frequency and severity. Plants may suffer severe acute or chronic hypoxia, resulting in substantial yield losses. In this paper, the biosynthesis, signaling and transport of CKs, the impact of flooding on plants and the associated hypoxia signaling pathway of the group VII ethylene response factors are reviewed. Furthermore, this review summarizes the involvement of CKs specifically in flooding stress. Our review illuminates that CKs act as key phytohormones in regulating a number of processes associated with flooding stress, including epinasty, adventitious root formation, leaf chlorophyll degradation and transpiration. A hypoxia-induced alteration in root cytokinin expression pattern reduces root CK levels, thereby lowering CK transport to the shoot, and concomitantly affects shoot growth. The precise molecular mechanisms governing cytokinin-mediated responses to hypoxia remain incomplete. Future research could investigate a direct association between oxygen sensing and the cytokinin pathway.