In this study, seeds of Hyoscyamus niger were exposed to different concentrations (50–800 g mL−1)of single-walled carbon nanotubes (SWCNTs) under different levels of drought stress (0.5–1.5 MPa) for14 days. Germinated seeds were subsequently allowed to grow in the same culture media for 7 moredays to test the further response of the seedlings in terms of biochemical changes to the employed treat-ments. Seeds subjected to drought showed reduction in germination percentage, vigor and lengths ofroots and shoots. However, inclusion of SWCNTs at the two lowest concentrations significantly alle-viated the drought stress (up to moderate levels only)-induced reduction in germination and growthattributes. This happened due to increased water uptake, up-regulation of mechanisms involved instarch hydrolysis, and reduction in oxidative injury indices including H2O2, malondialdehyde contentsand electrolyte leakage. The improved plant performance under PEG-induced drought stress was aconsequence of changes in the expression of various antioxidant enzymes including SOD, POD, CAT,and APX, and also biosynthesis of proteins, phenolics, and specific metabolites such as proline. Results demonstrate that treatment by low concentrations of SWCNTs can induce tolerance in seedlings againstlow to moderate levels of drought through enhancing water uptake and activating plant defense system.
