Proteomic and physiological analyses to elucidate nitric oxide-mediated adaptive responses of barley under cadmium stress

Nitric oxide (NO) is known to induce plant resistance for several environmental stresses. The protective roles of NO in cadmium (Cd) toxicity have been well documented for various plant species; nevertheless, little information is available about its molecular regulation in improving Cd tolerance of barley plants. Therefore, we combined a comparative proteomics with physiological analyses to evaluate the potential roles of NO in alleviating Cd stress (50 μM) in barley (Hordeum vulgare L.) seedlings. Exogenous application of NO donor sodium nitroprusside (SNP, 100 μM) decreased the Cd-mediated seedling growth inhibition. This observation was supported by the reduction of lipid peroxidation as well as the improvement of chlorophyll content and inhibition of hydrogen peroxide accumulation. Activities of the superoxide dismutase and guaiacol peroxidase were reduced following the application of SNP, while ascorbate peroxidase activity was enhanced. In this study, a total of 34 proteins were significantly regulated by NO in the leaves under Cd stress using a gel-based proteomic approach. The proteomic analysis showed that several pathways were noticeably influenced by NO including photosynthesis and carbohydrate metabolism, protein metabolism, energy metabolism, stress defense, and signal transduction. These results provide new evidence that NO induce photosynthesis and energy metabolism which may enhance Cd tolerance in barley seedlings.