INTERACTION BETWEEN MILD SALINITY AND SUBLETHAL SO2 POLLUTION ON WHEAT (TRITICUM-AESTIVUM CULTIVAR WILGOYNE (CIANO GALLO)) .2. ACCUMULATION OF SULFUR AND IONS

Wheat (Triticum aestivum cultivar 'Wilgoyne' (Ciano/Gallo)) plants were exposed to a factorial combination of two levels of salinity (control and 50 mM NaCl), and three levels of SO2 ( < 10, 231, and 441 nl l-1) in fumigation chambers with rain-exclusion tops for 4 h day-1 for up to 42 days. The study was to investigate whether mild salinity stress could influence the accumulation and reduction of SO2 absorbed and SO2 fumigation could modify the salt ion concentrations in the plant tissues. SO2 fumigation significantly increased sulphur concentration in the shoots, but not in the roots. The SO2 absorbed in the leaves was mostly oxidized into sulphate and little reduced into organic sulphur compounds. NaCl salinity decreased the sulphate concentration in leaves, but did not affect the organic sulphur concentration. There was an antagonistic interaction between SO2 fumigation and NaCl salinity on the concentration of sulphate in the leaves. SO2 fumigation, salinity, and their combination affected the concentrations of Cl-, K+, Na+, Ca2+ and Mg2+ in the plant tissues Exposure to SO2 increased the K+ concentration in the leaves, but decreased the Cl-, Ca2+ and Mg2+ concentrations. SO2 fumigation and NaCl salinity had an antagonistic interaction on the concentrations of K+, Cl-, Ca2+ and Mg2+ in the leaf tissue. The Na+ concentration in the youngest fully expanded leaves of the saline plants was decreased by exposure to 441 nl l-1 SO2. Plant tolerance to NaCl salinity may have been enhanced by SO2 fumigation by decreasing Na+ and Cl- concentration and increasing the K+ concentration in the leaves. The antagonistic interactions between SO2 fumigation and NaCl salinity on the SO2 uptake and salt accumulation in the leaves may be responsible for their antagonistic interaction on plant growth.