Role of foliar application of sodium nitroprusside on induction of antioxidant enzyme activities of narcissus (Narcissus tazetta L.) in response to saline water irrigation

The present experiment was aimed to investigate the improvement of salt tolerance in narcissus by exogenous application of sodium nitroprusside (SNP) in a factorial complete randomized block design with three replications at the Research Greenhouse, Islamic Azad University, Isfahan (Khorasgan) Branch during 2019-2020. Experimental treatments included irrigation by saline water at two levels 4 and 8 dS m-1 and control (without saline), as well as SNP (0, 100, 200, and 400 µM). The results indicated that elevated salt stress levels induce oxidative stress, including an increase in the hydrogen peroxide by 82% and malondialdehyde by 118% in plants. Severe salt stress reduced morphological traits, including a 40% decrease in flower longevity on the plant and a 49% decrease in the flowering duration of narcissus compared to non-stress conditions. The salt stress led to the change of antioxidant enzymes activities at different concentrations. The activity of superoxide dismutase enzyme positively correlated with salt treatment and increased up to 23%. While catalase enzyme increased up to 4 dS m-1 treatment by 87% and then decreased at a higher concentration in the leaves. However, SNP reduced oxidative damage in plants by improving antioxidant enzymes, proline and flavonoid content, ultimately, preventing the reduction of plant biomass. Finally, the present study showed that the exogenous application of SNP, especially at a concentration of 200 µM, improved narcissus tolerance to salinity stress by reducing the uptake of Na by 16%, as well as decreasing membrane lipid peroxides by 17%.