[en] Wheat, Triticum vulgare and spinach, Spinacia oleracea plants were exposed to two different concentrations of ³⁵SO₂ - released by lactic acid from Na₂³⁵SO₃ - for 45 minutes, and distribution of radioactivity was studied in leaves, stem and roots. After 24 hours, the specific activity of the leaves of both plants was reduced while that of the roots was increased, suggesting ³⁵S translocation from leaves to roots. Translocation to the stem and roots of ³⁵S products was much higher in wheat than in spinach. In leaves of both plant species, ethanol-soluble products were much higher than the ethanol-insoluble fraction during the first 6 hours of exposure. The ethanol-soluble fraction contained sulphate, sulphite and unidentified material. The study suggests that SO₂ is metabolized in preference to endogenous S, that the wheat plant is more susceptible to SO₂, and that tolerance is related to the capacity of converting SO₂ to sulphate and reducing its further conversion. Uptake of ³⁵SO₂ by young and old wheat and spinach plants was studied with a view to determining susceptibility to SO₂ exposure as a function of the developmental stage of the plant. In wheat, young plants metabolize endogenous sulphur in preference to absorbed SO₂ while older plants are active in converting absorbed sulphur into organic (ethanol-insoluble) form. In spinach, young plants are more active in transporting ³⁵S products from leaves to roots and older plants show higher incorporation percentage of ³⁵S into the organic fraction of leaves. Uptake of 1-¹⁴C-acetate by lipids of leaf discs from spinach and wheat was investigated in normal and SO₂-stressed plants. The incorporation of radioacetate into lipids of leaf tissues of both plants was strongly inhibited in SO0 plants. Also U-¹⁴C-lysine incorporation into proteins of leaf tissue was significantly inhibited by 0.2-2.0 ppm aqueous SO₂