AMF-mediated systemic regulation induces Zn-deficiency tolerance through nutrient and metabolic adjustment in pea plants

Zinc (Zn) deficiency limits plant growth and productivity, yet the role of arbuscular mycorrhizal fungi (AMF) in Zn-deficiency tolerance in pea plants remains unclear. In this study, we investigated the effect of Rhizophagus irregularis on pea plants exposed to Zn deficiency in hydroponic conditions. Microscopic observation and qPCR-based quantification of AMF abundance confirmed successful colonization only in AMF-inoculated plants, accompanied by the presence of different AMF structures in the roots. Zn deficiency severely impaired plant health, resulting in reduced biomass, photosynthetic parameters, and Zn status in tissues. Zn deficiency also increased hydrogen peroxide accumulation, electrolyte leakage, and altered mineral homeostasis. However, AMF inoculation significantly alleviated these detrimental effects by improving growth performance, photosynthetic traits, and Zn accumulation under Zn-deficient conditions. AMF further induced the expression of Zn transporter-related genes ( ZIP1 and ZIP2 ), suggesting enhanced Zn acquisition in inoculated plants. In addition, Zn deficiency caused substantial reprogramming of amino acid metabolism, characterized by increased stress-associated amino acids and reductions in several growth-related amino acids, including leucine, isoleucine, glycine, and tyrosine. AMF inoculation restored several of these metabolites under Zn-deficient conditions, indicating metabolic adjustment associated with stress recovery and physiological stabilization. Importantly, split-root analysis showed improved shoot growth, biomass, and chlorophyll status even when AMF colonized only one portion of the root system, providing evidence for systemic regulation. Overall, these findings demonstrate that AMF alleviate Zn deficiency through coordinated regulation of Zn acquisition, metabolic adjustment, and systemic physiological responses, highlighting their potential for improving plant performance under Zn-limited conditions.