Possible Implications of Heavy Metals (Pb²⁺ and Hg²⁺) in the Free Radical - Mediated Membrane Damage in Two Rice Cultivars.

When seeds of two cultivars of rice (Oryza sativa L.) viz. Ratna and IR36, were subjected to heavy metal (Pb²⁺ and Hg²⁺) stress, an increase in leakage of electrolytes Was observed. The increase was more pornounced in Ratna than in IR36 and the root was more affected than the shoot. The injury index data also corroborated the above results. Malondialdehyde content and lipoxygenase activity also increased by treatments with both heavy metals. Pb²⁺ increased the activity of catalase and peroxidase and decreased the activity of superoxide-dismutase (SOD) and the H₂O₂ level. On the other hand, Hg²⁺ increased the activity of peroxidase and the level of H₂O₂ while decreasing the activity of SOD and catalase. It was concluded that the membrane damage was mediated by reactive oxygen species and hydroperoxides induced by Pb²⁺ and Hg²⁺ and Ratna was more susceptible to these metals than IR36.