Sulfonated graphene-induced hormesis is mediated through oxidative stress in the roots of maize seedlings

The present study investigated the impact of sulfonated graphene (SG) on the growth of maize seedlings at a concentration range of 0-500mgL^-1. Stress-related parameters including reactive oxygen species (ROS), intracellular Ca²⁺, antioxidant enzyme activities, lipid peroxidation, membrane leakage, cell death and root morphology were examined to reveal the potential mechanisms. The results indicate that SG induced a hormesis effect on plant height, i.e., low-concentration (50mgL^-1) stimulation and high-concentration (500mgL^-1) inhibition. The hormesis effect of SG on plant height was directly correlated with ROS levels in roots. A low concentration (50mgL^-1) of SG promoted ROS scavenging, alleviated oxidative stress, enhanced the soluble protein (SP) content, and decreased intracellular Ca²⁺ and cell death in the roots. At a higher concentration (500mgL^-1), SG stimulated the generation of ROS in the roots, decreased SP content in the leaves, increased antioxidant enzyme activities, intracellular Ca²⁺, electrolyte leakage and cell death in the roots, and increased the malondialdehyde (MDA) content in both roots and leaves. Different changes were observed for root morphology at SG concentrations of 50 and 500mgL^-1, and a larger amount of SG was deposited onto the root surface at a concentration of 500mgL^-1 compared with 50mgL^-1.