| humic substances (HS) is one of the most stable forms of organic matter with biological activity in vitro. This article reviews the chemical composition, structural characteristics and physiological activity of HS, and discussed the internal mechanism of the physiological activity based on the relationship between its chemical composition, structural characteristics and physiological activity. The chemical composition of HS is uncertain, and the supramolecular structure model of HS is currently generally accepted. HS promotes absorption and utilization of mineral elements by promoting formation of root hairs and lateral root development, activating plasma membrane H+-ATPase to generate favorable electrochemical gradients, and chelating mineral elements with acidic functional groups. With hormone-like activity, HS IAA secreted by plant rhizosphere growth-promoting bacteria (PGPR) or HS autologous component can activate plasma membrane H+-ATPase. HS can also increase endogenous plant hormone levels and promote plant growth and development. HS activates plasma membrane H+-ATPase by mediating messenger NO to eliminate reactive oxygen species (ROS) generated from HS-affected cells. HS mediates root development and morphological structure by regulating intracellular ROS homeostasis through NO and antioxidant enzymes. This article also focuses on the correlation between HS physiological activity and its chemical composition; the role of active sites such as -COOH and -OH, the electron transfers of quinone groups, and HS hydrophilic-hydrophobic balance are closely related to HS physiological activities. The focus of future HS research work is to in-depth study of HS molecular structure, clarify the "common structural element" with physiological activity, of the cross-feedback mechanism between HS-induced intracellular signal transduction pathways, and reveal the regulation mechanism of HS on gene expression related to material and energy metabolism in cells, aiming to provide theoretical basis for in-depth study of HS physiogical activity mechanism and afterward agricultural application. |
