Resistance to Injury by Sulfur Dioxide 1: Correlation with Its Reduction to, and Emission of, Hydrogen Sulfide in Cucurbitaceae

In Cucurbitaceae young leaves are resistant to injury from acute exposure to SO₂, whereas mature leaves are sensitive. After exposure of cucumber (Cucumis sativus L.) plants to SO₂ at injurious concentrations, illuminated leaves emit volatile sulfur, which is solely H₂S. Young leaves emit H₂S many times more rapidly than do mature leaves. Young leaves convert approximately 10% of absorbed [³⁵S]SO₂ to emitted [³⁵S]H₂S, but mature leaves convert less than 2%. These results suggest that a high capability for the reduction of SO₂ to H₂S and emission of the H₂S is a part of the biochemical basis of the resistance of young leaves to SO₂.