Responses of nitrogen metabolism parameters to sublethal SO 2 pollution in wheat [ Triticum aestivum cv Wilgoyne (Ciano/Gallo)] under mild NaCl stress

Abstract

Wheat plants were exposed to a factorial combination of two levels of salinity (control and 50 mM NaCl), and three levels of SO 2 (<10, 231, and 441 nl l −1) in fumigation chambers with rain-exclusion tops for 4 hr day −1 for up to 51 days. Exposure to 441 nl l −1 SO 2 initially increased nitrate reductase activity (NRA) in the youngest fully expanded leaves, but it decreased later. NRA was decreased more in older leaves than in young leaves with SO 2. Nitrogen utilization, but not uptake into plants, appeared to be affected by SO 2 fumigation, resulting in an increase in total amino acid concentration and soluble protein in the old leaves. NaCl treatment decreased nitrogen uptake rate per unit root dry weight. Concentrations of total amino acids and soluble protein increased with NaCl salinity. Both NaCl and SO 2 increased concentrations of total amino acids and soluble protein in leaves. Generally, effects of SO 2 fumigation and NaCl salinity were additive on nitrogen uptake rate g −1 root dry wt, leaf NRA, total nitrogen concentration, and total amino acid concentration in plants.