Mycorrhiza-induced cadmium tolerance in squash: roles of antioxidant defense, secondary metabolites, and restricted metal uptake and translocation

Abstract

Climate change-associated environmental pollution has intensified heavy metal contamination, particularly cadmium (Cd), posing a serious threat to agricultural productivity and food safety. The present study investigated the potential role of arbuscular mycorrhizal fungi (AMF) in mitigating Cd-induced toxicity in squash plants cultivated under Cd-stressed soil conditions (100 µM Cd). For this purpose, four treatments were performed, i.e., Group I- Control; Group II- Cd (100 µM); Group III- AMF; Group IV- AMF + Cd (100 µM). Exposure to Cd markedly suppressed squash growth and physiological performance, as evidenced by reductions in root biomass (fresh: 18.18% and dry: 20.92%), shoot height (11.32%), root length (12.32%), chlorophyll contents (19.05%) and Carotenoids (19.32%) accompanied by excessive Cd accumulation in both roots and shoots. Cd stress also induced severe oxidative damage through increased hydrogen peroxide (H2O2) production. In contrast, AMF inoculation substantially alleviated Cd toxicity by significantly improving morphological and physiological traits relative to Cd-stressed plants. AMF treatment enhanced chlorophyll content (11.40%) and Carotenoids (16.76%), reduced H2O2 accumulation, and stimulated osmoprotective and antioxidative defense systems. Specifically, AMF significantly increased proline and protein contents, along with the activities of peroxidase, ascorbate peroxidase, polyphenol oxidase, and catalase. Furthermore, AMF restricted Cd uptake and reduced its translocation from roots to shoots, indicating improved metal sequestration and limited Cd mobility within plant tissues. Enhanced accumulation of secondary metabolites, particularly total phenolics and flavonoids, was also observed in AMF-inoculated plants under Cd stress. Overall, AMF effectively mitigated Cd-induced phytotoxicity in squash plants through modulation of antioxidant defense mechanisms, osmolyte accumulation, secondary metabolite biosynthesis, and limitation of Cd translocation. These findings highlight the promising potential of AMF as an eco-friendly and sustainable strategy for improving plant tolerance and productivity under heavy metal-contaminated conditions.