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 I rice than in Tainung 67. The differences in peroxidase (PDX) activity and lignin content between Cd-tolerant and Cd-sensitive rice varieties were compared. In our study, PDX activity in Tainting 67 increased significantly in Cd-treated tissues. However, enhanced PDX activity in Cd-treated tissues was accompanied by a H2O2 decrease. The H2O2 accumulation in the Cd-treated tissues of Taichung Native 1 rice may be due to the lower amount of PDX enhancement induced by Cd. The increased activity in cationic (pI 8.6) and anionic (pI 4.5) PDXs correlated with the increase in PDX transcripts, and therefore was mostly due to the de novo synthesis of the cationic (pI 8.6) and anionic (pI 4.5) PDXs in Cd-treated roots of Tainung 67. For promoter analysis, Tainting 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 I (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 PDX synthesis, which leads to the production of more lignin to deal with Cd stress.