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 μg 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 ½ MStreated 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 μg mL−1, NGO significantly increased total phenolic (40.9%) and flavonoid (35.3%) contents, but significantly reduced proline (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.
