Mechanisms underlying toxicity and stimulatory role of single-walled carbon nanotubes in Hyoscyamus niger during drought stress simulated by polyethylene glycol.

In this study, seeds of Hyoscyamus niger were exposed to different concentrations (50-800μgmL-1 ) of single-walled carbon nanotubes (SWCNTs) under different levels of drought stress (0.5-1.5MPa) for 14days. Germinated seeds were subsequently allowed to grow in the same culture media for 7 more days to test the further response of the seedlings in terms of biochemical changes to the employed treatments. Seeds subjected to drought showed reduction in germination percentage, vigor and lengths of roots and shoots. However, inclusion of SWCNTs at the two lowest concentrations significantly alleviated the drought stress (up to moderate levels only)-induced reduction in germination and growth attributes. This happened due to increased water uptake, up-regulation of mechanisms involved in starch hydrolysis, and reduction in oxidative injury indices including H2 O2 , malondialdehyde contents and electrolyte leakage. The improved plant performance under PEG-induced drought stress was a consequence 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 against low to moderate levels of drought through enhancing water uptake and activating plant defense system.