Symbiotic Fungus Serendipita indica as a Natural Bioenhancer Against Cadmium Toxicity in Chinese Cabbage

Heavy metal toxicity, particularly cadmium (Cd), poses a growing threat to agriculture and human health due to its persistence and high solubility, which facilitates its entry into the food chain. Among the strategies proposed to reduce Cd toxicity in plants and the environment, the use of beneficial microorganisms, such as endophytic fungi, has gained attention due to its effectiveness and eco-friendliness. This study investigates the potential of the root-colonizing fungus <i>Serendipita indica</i> (formerly <i>Piriformospora indica</i>) to mitigate cadmium (Cd) stress in Chinese cabbage (<i>Brassica rapa</i> L. subsp. <i>Pekinensis</i>) grown hydroponically under varying Cd concentrations (0, 1, 3, and 4 mM). Several parameters were assessed, including morphological traits, physiological and biochemical responses, and changes in leaf composition. Exposure to Cd significantly reduced plant growth, increased membrane electrolyte leakage, and decreased relative water content and root colonization, while enhancing antioxidant enzyme activities and the accumulation of phenolics, flavonoids, proline, glycine betaine, and carbohydrates. Notably, plants treated with <i>S. indica</i> showed improved tolerance to Cd stress, indicating the potential of the fungus. These findings suggest that <i>S. indica</i> can enhance plant resilience in Cd-contaminated environments and may offer a promising biological strategy for sustainable crop production under heavy metal stress.