Effects of exogenous nitric oxide on photosynthetic, bioluminescent characteristics and mineral element contents in tomato under copper stress

Nitric oxide (NO) serves as a bioactive molecule involved in antioxidant and anti-stress agent in tolerance responses to abiotic stress. A hydroponic experiment was conducted to investigate the effects of exogenous sodium nitroprusside (SNP), a NO donor, on photosynthetic characteristics, bioluminescence intensity, chlorophyll and mineral element contents in tomato (Lycopersicon esculentum Mill.) plants treated with 50 μmol/L CuCl2. The application of 100 μmol/L SNP significantly increased chlorophyll contents, net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), copper(Cu), calcium (Ca), iron (Fe), zinc (Zn), manganese (Mn) contents in leaves and copper(Cu), potassium (K), iron (Fe), zinc (Zn) contents in roots; and dramatically decreased ultraweak luminescence intensity, fluorescence intensity, phosphorescence intensity and calcium (Ca) content in roots induced by CuCl2. While the mitigate response of SNP to Cu stress were inhibited by addition of hemoglobin (a NO scavenger). No significant difference on photosynthetic, bioluminescent characteristics and mineral element contents in tomato was observed by the application of sodium nitrate or nitrite (the decomposition products of NO or its donor SNP) or sodium ferrocyanide (an analog of SNP) which did not release NO. We concluded that exogenous NO could improve photosynthetic characteristics, decrease ultraweak luminescence intensity, fluorescence intensity, phosphorescence intensity, maintain the mineral nutrition balance, alleviate the inhibition of tomato by copper stress.