Endogenous nitric oxide contributes to chloride and sulphate salinity tolerance by modulation of ion transporter expression and reestablishment of redox balance in Brassica napus cultivars

Salinity is an adverse environmental stress for crop plants and the mechanism of salinity tolerance and its interaction with phytohormone like nitric oxide (NO) is still lacking, especially for Na₂SO₄ in B. napus. Therefore, in the present study, B. napus cultivars were grown under equimolar concentrations of NaCl/Na₂SO₄ and with their anions (KCl/K₂SO₄), to discriminate toxic responses of different types of salts on growth, oxidative stress, antioxidant defense, anion concentration and endogenous production of NO. Results showed that plant growth, photosynthetic rate and pigments productions were strongly inhibited under Na⁺ dominated salt treatments (NaCl/Na₂SO₄). As a result, production of oxidative stress (H₂O₂, O₂.⁻, MDA, EL) related parameters were significantly induced under these treatments. The uptake of Na⁺ was high in B. napus cultivars irrespective of chloride/sulphate anions presence. However, Cl⁻ and SO₄²⁻ anions accumulation was only high in sensitive cultivars. The differential responses of B. napus cultivars against salinity treatments were associated with endogenous production of NO. The tolerant cultivar maintained higher level of NO, while sensitive cultivars experience a reduction in NO and inhibition of its biosynthesis enzymes, upon exposure to salinity treatments. To prove NO involvement, NO scavenger was applied on the leaves of B. napus cultivars, which significantly induced salt toxicity symptoms, oxidative stress and upregulated gene expression of ion transporters and uptake of Na⁺, Cl⁻ and SO₄²⁻. Conversely, application of NO donor (sodium nitroprusside) reversed the salinity induce oxidative stress, ion accumulation and stimulated antioxidant defense in B. napus cultivars. Thus, the present study shows that endogenous NO level could act as an essential signaling molecule for triggering and activating the salinity adaptive response in rapeseed and Na⁺ toxicity plays a dominate role in growth inhibition, while the additive effect of chloride/sulphate anions may be cultivar dependent.