Effect of cadmium on peroxidase isozyme activity in roots of two Oryza sativa cultivars

Cadmium (Cd) decreased the growth of rice expressed as fresh weight. Root growth was inhibited more severely in Taichung Native 1 rice than in Tainung 67. The differences in peroxidase (POX) activity and lignin content between Cd-tolerant and Cd-sensitive rice varieties were compared. In our study, POX activity in Tainung 67 increased significantly in Cd-treated tissues. However, enhanced POX activity in Cd-treated tissues was accompanied by a H ₂O ₂ decrease. The H ₂O ₂ accumulation in the Cd-treated tissues of Taichung Native 1 rice may be due to the lower amount of POX enhancement induced by Cd. The increased activity in cationic (pI 8.6) and anionic (pI 4.5) POXs correlated with the increase in POX transcripts, and therefore was mostly due to the de novo synthesis of the cationic (pI 8.6) and anionic (pI 4.5) POXs in Cd-treated roots of Tainung 67. For promoter analysis, Tainung 67 (Japonica type) owned ten conserved cores of CURECORECR sequence (5'-GTAC-3'), a copper-response element (CuRE), involved in heavy metals response. Taichung Native 1 (Indica type) had only eight CURE. This implies that a Cd-tolerant cultivar, Tainung 67 (Japonica type), may receive more signals with Cd treatment, enhancing more POX synthesis, which leads to the production of more lignin to deal with Cd stress.