MWCNTs (Multi-walled carbon nanotubes), as an important nanomaterial, enters the soil through various anthropogenic sources. Our understanding of MWCNTs effects on plant growth is still not complete and needs to be more studied. In this study, the possible effects of MWCNTs (500, 1000 and 2000 mg kg -1 ) and 100 μM exogenous sodium nitroprusside (SNP, as NO donor) on growth, physiological and photosynthetic performance of barley plants under 100 and 200 mM NaCl stress were investigated in

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... ouse conditions. The most of physiological and photosynthesis characteristics of barley seedling negatively impressed when the plants were grown in different concentrations of NaCl. In the presence of SNP, 500 mg kg -1 dosage of MWCNTs significantly enhanced relative water content (RWC), chlorophyll content, photosynthesis parameters and growth indices. Also, MWCNTs-treated plants combined with 100 μM SNP showed higher antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and lower malonyldialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) content under salinity stress. It is suggested that, MWCNTs in presence of SNP can greatly improve growth, as well as salt tolerance of barley plant by promoting water uptake, activities of antioxidant enzymes and photosynthesis performance.