The interaction effects of NaCl stress and sodium nitroprusside on growth, physiological and biochemical responses of Calendula officinalis L

Sodium nitroprusside (SNP), as a nitric oxide (NO) donor, has well-documented properties for increasing plant tolerance to environmental stresses such as salinity. Here, we evaluated the effect of SNP (0, 50 and 100 mu M) on growth, metabolism of chlorophyll, proline and glutathione (GSH), ionic homeostasis, nitrate reductase, the antioxidant defense system and the glyoxalase system in pot marigold (Calendula officinalis) under NaCl (0, 50, 100 and 150 mM) treatments. The results showed that 100 and 150 mM NaCl reduced photosynthetic pigments and plant growth by diminishing nutrient uptake (K, Ca, P and N) and disrupting ionic homeostasis as well as increasing the levels of toxic compounds (hydrogen peroxide, methylglyoxal and superoxide anion) and inducing oxidative stress. SNP application improved the performance of photosynthetic apparatus and increased the plant growth and biomass under salinity by modulating chlorophyll metabolism. SNP also increased proline and GSH and improved plant salinity tolerance by inducing proline and GSH metabolisms. SNP increased the K/Na ratio and maintained ion homeostasis under salinity by decreasing the uptake of Na and Cl and increasing the uptake of K, P, N and Ca. By inducing the activity of enzymes involved in the antioxidant defense system and the glyoxalase system, SNP diminished the level of toxic compounds and mitigated oxidative stress under salinity. Our results revealed that concentrations of more than 100 mM NaCl can induce salt stress in pot marigolds; however, the exogenous application of SNP as a stress alleviator can improve pot marigold tolerance under salinity.