Progress and perspective in research on plant resistance mediated by root exudates

Root exudates are a variety of biochemical substances actively or passively secreted by plant roots that play an important role in mediating material exchange, energy transfer and information exchange in plant rhizosphere microenvironments, as well as in plant responses to environmental stresses. Biotic and abiotic stresses can change the composition and quantity of root exudates and increase the content of defensive compounds in plant root exudates. Plants use different root exudates to resist biotic and abiotic stresses, including releasing toxic substances for direct defense, releasing volatile substances to attract natural enemies, interacting with microorganisms to resist biotic stresses, releasing root exudates with osmotic regulation and antioxidant capacity and coordinating hormone signals to resist abiotic stress. Additionally, root exudate flow increases the concentration of many common metabolites, changing the soil physical and chemical properties and microbial activities, and affecting the physiological and biochemical processes at the soil-plant interface, thereby, directly or indirectly improving plant stress resistance. In this paper, the effects of biotic and abiotic stresses on the composition and quantity of plant root exudates were reviewed, the mechanisms of plant defense against biotic and abiotic stresses mediated by root exudates were summarized, and the aspects needed to be further studied were also suggested, to provide a reference for further research on the adaptive mechanism of plants under stress.