Effect of SO2 on Ascorbic Acid Content in Crop Plants --First Line of Defence against Oxidative Stress

Effect of different SO₂ concentrations on the ascorbic acid content in the leaves of three economically important plant species, viz., Vigna radiata (Mung bean), Solanum esculentum (= Lycopersicon esculentum)[Tomato] and Zea mays (Maize) was studied . Controlled fumigation experiments were carried out using three different treatments of SO₂ : T-1 = 0.05 ppm (134.0µg m^-3 SO₂) [x 4h], T-2 = 0.1 ppm(268.0 µg m^-3 SO₂) [x 2h] and T-3 = 0.2 ppm (536.0 µg m^-3 SO₂) [x 1h] for 60 days. Whereas SO₂ fumigation resulted in a progressive decrease in ascorbate content in both mung bean and tomato, there was in fact, a marginal increase in ascorbate in T-1 of Z.mays after 30 days followed by negligible reduction in the subsequent treatments. These studies highlight a positive correlation between ascorbic acid content and SO₂-sensitivity of plants and indicate that Z.mays exhibits a relatively greater resistance to SO₂-stress.