Antioxidant enzyme activities are upregulated in response to cadmium in sensitive, but not in tolerant, rice (Oryza sativa L.) seedlings

Abstract

Changes in H 2 O 2 and malondialdehyde (MDA) contents and antioxidant enzyme activities in Cd-treated rice (Oryza sativa L.) seedlings of two cultivars were investigated. On treatment with CdCl 2 , increases in H 2 O 2 and MDA contents and antioxidant enzyme activities (speroxide dismutase (SOD), ascorbate peroxidase, glutathione reductase, catalase, and peroxidase (POX)) were observed in the leaves of Cd-sensitive cultivar (cv. Taichung Native 1, TN1) but not in Cd-tolerant cultivar (cv. Tainung 67, TNG67). The increased content of MDA and activities of SOD and POX preceded the occurrence of toxicity in CdCl 2 -treated TN1 leaves. Pretreatment with abscisic acid (ABA) enhanced Cd tolerance and reduced Cd-induced increase in the content of MDA and increase in the activities of SOD and POX in TN1 leaves. Exogenous application of ABA biosynthesis inhibitor, fluridone, decreased Cd tolerance, increased the content of MDA, and increased the activities of SOD and POX in Cd-treated TNG67 leaves. Furthermore, fluridone's effects on toxicity, the content of MDA, and the activities of SOD and POX in Cd-treated TNG67 leaves were reversed by the application of ABA. In conclusion, the oxidative stress is differently expressed in TN1 and TNG67 rice seedlings in response to CdCl 2 . Results also suggest that CdCl 2 causes an oxidative stress and CdCl 2 -induced toxicity is mediated through oxidative stress in TN1 leaves.