Effect of sulfur dioxide on physiological responses, cysteine, and glutathione in pepper and eggplant

This study was carried out to investigate the photosynthetic rate, water use efficiency, chlorophyll content, morphological changes, and cysteine and glutathione contents of pepper and eggplant plants treated with 50 µg·kg^-1 sulfur dioxide (SO₂) in a controlled environment chamber. Plants were treated with 50 µg·kg^-1 SO₂ for 24 h/day in a naturally irradiated phytotron. After exposure, SO₂ damage was examined by evaluating photosynthetic rate, water use efficiency (WUE), chlorophyll and carotenoid content, visible injury, stomata characteristics, and cysteine and glutathione content. The photosynthetic rate was significantly lower in treated plants compared to the control, and WUE increased with the SO₂ treatment in both pepper and eggplant compared to untreated plants. The chlorophyll and carotenoid content also decreased in plants treated with SO₂. The visible injury to leaves appeared after about 14 d of SO₂ exposure in pepper and 18 d after SO₂ exposure in eggplant. The leaves had yellow and white spots on their surface in both the pepper and eggplant plants. Over a period of SO₂ exposure, necrosis was observed in both pepper and eggplant leaves. Stomatal density and size decreased in response to SO₂ exposure in both of pepper and eggplant. The cysteine and glutathione levels significantly increased after SO₂ exposure in both pepper and eggplant.