Nano‐Biointerface of Magnesium–Selenium Nanocomposites Enhance Stress Tolerance in Eggplant ( Solanum melongena ) Under Cadmium Toxicity

Cadmium (Cd) toxicity severely impairs plant growth, physiology, and biochemical processes. This study investigated the effectiveness of nanoparticle‐based supplements (NCs‐I and NCs‐II) in alleviating Cd‐induced stress in eggplant ( Solanum melongena L.). Cadmium stress significantly reduced root length (41.11%), shoot length (26.97%), shoot fresh weight (35.02%), shoot dry weight (18.08%), chlorophyll a (62.38%), chlorophyll b (81.60%), carotenoids (43.17%), photosynthetic rate (32.44%), stomatal conductance (60.00%), transpiration rate (37.35%), and selenium accumulation in shoots (58.59%) and roots (66.67%). In contrast, Cd stress increased malondialdehyde (MDA) by 36.32%, hydrogen peroxide (H 2 O 2 ) by 77.27%, relative membrane permeability by 58.97%, electrolyte leakage by 47.06%, and proline accumulation by 76.52%, indicating severe oxidative damage. Application of NCs‐I and NCs‐II markedly mitigated Cd toxicity. Compared with Cd treatment alone, Cd + NCs‐II enhanced root length, shoot length, shoot fresh weight, and shoot dry weight by 116.83%, 59.49%, 71.86%, and 47.87%, respectively. Chlorophyll a, chlorophyll b, and carotenoid contents increased by 187.34%, 247.83%, and 193.52%, while relative water content improved by 43.89%. Photosynthetic rate, stomatal conductance, and transpiration rate increased by 62.30%, 185.00%, and 223.08%, respectively. Antioxidant defense was strengthened through increases in CAT (29.41%), POD (31.32%), and APX (71.64%) activities. Furthermore, Cd + NCs‐II enhanced shoot and root selenium accumulation by 235.66% and 377.81%, respectively, while restoring ionic balance through substantial increases in K + , Ca 2+ , and Mg 2+ contents. NCs‐I alone produced the highest improvements in several physiological traits, including chlorophyll content, photosynthetic efficiency, antioxidant enzyme activity, and water status.