Potential toxicity of nano-graphene oxide on callus cell of Plantago major L. under polyethylene glycol-induced dehydration

Graphene-based nanomaterials have shown a great potential towards improving plant performance in various contexts. However, their increased application over the last few years has raised concerns about their potential biological and environmental risks, warranting optimization and safety assessment considerations. The current study was performed to explore the potential impacts of nano-garphene oxide (NGO) at various concentrations (100-800 mu g mL(-1)) on morphological, physiological and biochemical responses of Plantago major L. calli cultures under normal and polyethylene glycol-induced drought stress conditions. Leaf-derived calli on the 1/2 MS treated medium with polyethylene glycol showed a decrease in relative growth rate (78.5%), osmotic potential value (48.2%) and an increase in dry matter (35.1%) and H2O2 (54.2%) contents at the highest employed NGO concentration compared with control (p < 0.05). The engineered NGO affected secondary metabolites and amino acid contents under normal water availability as well: at 800 mu g mL(-1), NGO significantly increased total phenolic (40.9%) and flavonoid (35.3%) contents, but significantly reduced praline (26.9%) content compared to the respective control. The integrated biological marker (IBR/n) index for antioxidant enzymes (SOD, CAT, POD, and APX) activities was differentially influenced by the experimental treatments. Overall, the results demonstrated that NGO can positively affect the performance of P. major L. calli cells when applied at specific concentrations, and provide useful inputs into the further studies on phytotoxicity assessment of NGO.