Exogenous application of nitric oxide promotes growth and oxidative defense system in highly boron stressed tomato plants bearing fruit

• Exogenous application of NO partly mitigated the damaging effects of B toxicity in tomato plants.
• Exogenous application of NO could modulate oxidative defense system in tomato plants.
• Exogenous NO reduced the concentrations of B, MDA and H2O2 as well as electrolyte leakage in tomato plant leaves.

To assess the effectiveness of foliage spray of nitric oxide (NO) on some key physio-biochemical variables of tomato (Lycopercison esculentum cv. ‘Target NF1’) plants subjected to boron (B) toxicity, a glasshouse trial was established. A factorial experiment was conducted with three levels of B (0.5, 3.5 and 6.5 mg/L) and 0 or 0.1 mM NO as foliar spray. Boron toxicity caused marked decrease in dry matter and fruit yield in tomato plants as compared to non-stresses plants, but increased electrolyte leakage (EL), proline, malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents coupled with superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7), catalase (CAT; EC. 1.11.1.6) activities and total antioxidant activity (TAA). However, exogenous application of NO partly mitigated the damaging effects of B toxicity on key growth parameters which due to low membrane permeability, H2O2 and MDA contents, TAA and antioxidant enzyme activities. Leaf B was higher in tomato plants at B treatments than that in the control plants. High B reduced leaf Ca2+, N and K+ as compared to those in the control plants. Foliar application of NO lowered B concentration and increased Ca2+, K+ and N levels in the leaves. The study clearly reveals that exogenous NO can overcome the deleterious effects of B toxicity on tomato fruit yield and whole plant biomass by reducing the concentrations of B, MDA and H2O2as well as electrolyte leakage in the leaves.