No data to date are available on the underlying mechanisms by which coumarin (COU) alleviates plant aluminum (Al) toxicity. Citrus grandis (L.) Osbeck seedlings were submitted to 0 (Al0) or 1.2 (Al1.2 or Al3+ toxicity) mM AlCl3·6H2O and 0 (COU0) or 50 (COU50) μM COU for 18 weeks. The results demonstrated that COU50 attenuated Al1.2-induced decreases of seedling growth, chlorophyll (Chl) level, and CO2 assimilation (ACO2) and impairment of the photosynthetic electron transport chain (PETC). Further analysis suggested that reduced tissue Al concentration and enhanced capability to maintain nutrient and redox homeostasis played a role in COU-mediated amelioration of seedling growth inhibition, leaf Chl and ACO2 decline, and PETC impairment. Notably, seedlings treated with COU0 showed some adaptive responses to Al1.2. For example, Al1.2 decreased the biosynthesis and accumulation of proteins and amino acids to meet the increased need for energy; increased the diphenylpicrylhydrazyl (DPPH) scavenging activity and phenolic compound accumulation to meet the elevated demand for reactive oxygen species (ROS) and Al detoxification; and increased the accumulation of soluble sugars (glucose, fructose, and sucrose) to meet the augmented demand for ROS scavenging and energy. To conclude, the research revealed some mechanisms for COU-mediated amelioration of plant Al3+ toxicity.
Yang et al. (Sat,) studied this question.