Cu-II-directed self-assembly of fullerenols to ameliorate copper stress in maize seedlings

Widespread use of copper-based agrochemical may cause copper excessive accumulation in agricultural soil to seriously threaten crop production. Recently, fullerenols are playing important roles in helping crops build resistance to abiotic stresses by giving ingenious and successful resolutions. However, there is a lack of knowledge on their beneficial effects in crops under stresses induced by heavy metals. Herein, the visual observation of Cu²⁺-mediated assembly of fullerenols via electrostatic and coordination actions was carried out in vitro, showing that water-soluble nanocomplexes and water-insoluble cross-linking nanohybrids were selectively fabricated by precisely adjusting feeding ratios of fullerenols and CuSO₄. Furthermore, maize simultaneous exposure of fullerenols and CuSO₄ solutions was tested to investigate the comparative effects of seed germination and seedling growth relative to exposure of CuSO₄ alone. Under moderate Cu²⁺ stresses (40 and 80 μM), fullerenols significantly mitigated the detrimental effects of seedlings, including phenotype, root and shoot elongation, biomass accumulation, antioxidant capacity, and Cu²⁺ uptake and copper transporter-related gene expressions in roots. Under 160 μM of Cu²⁺ as a stressor, fullerenols also accelerated germination of Cu²⁺-stressed seeds eventually up to the level of the control. Summarily, fullerenols can enhance tolerance of Cu²⁺-stressed maize mainly due to direct detoxification through fullerenol-Cu²⁺ interactions restraining the Cu²⁺ intake into roots and reducing free Cu²⁺ content in vivo, as well as fullerenol-maize interactions to enhance resistance by maintaining balance of reactive oxygen species and optimizing the excretion and transport of Cu²⁺. This will unveil valuable insights into the beneficial roles of fullerenols and its mechanism mode in alleviating heavy metal stress on crop plants.