AMF-Mediated samarium tolerance in Avena sativa: Insights into primary metabolism, amino acid biosynthesis, and flavonoid accumulation

Samarium (Sm), a rare earth heavy metal, poses significant threats to plant health and productivity. In oat plants, elevated Sm exposure reduced grain yield by up to 60% and decreased photosynthetic efficiency by 43.2–60%. This decline in photosynthesis led to reduced growth due to energy deficiencies. Sm stress also caused metabolic imbalances and oxidative stress. Inoculation with arbuscular mycorrhizal fungi (AMF) mitigated these negative impacts. AMF symbiosis reduced Sm accumulation in plant tissues, improving grain yield by up to 33.9%. AMF also maintained photosynthetic activity, limiting its decline to only 2.5%. This was reflected in enhanced primary metabolism, with increased glucose and starch synthase activity providing better sugar availability. AMF stimulated the synthesis of amino acids (e.g., phenylalanine, arginine), organic and fatty acids. The activation of nitrogen metabolism enzymes like GS and GDH further supported the synthesis of these amino acids. Subsequently, these increased amino acids acted as vital precursors for secondary metabolites, notably flavonoids, phenolics and tocopherols (increased by 24.2–33.6%). By restoring nutrient levels and modulating metabolic pathways, AMF effectively mitigated Sm's detrimental effects, contributing to plant recovery and metabolic flexibility under stress. Overall, AMF inoculation enhanced plant resilience to Sm stress.