Enhancement of Cd tolerance in transgenic tobacco plants overexpressing a Cd-induced catalase cDNA

Catalase (CAT), an important enzyme of antioxidant system, was investigated the role in preventing the plant from Cd-induced oxidative stress caused by reactive oxygen species. A CAT gene from Brassica juncea was cloned and up-regulated in response to Cd/Zn. The CAT cDNA (BjCAT3) under the control of CaMV35S promoter was introduced into tobacco via Agrobacterium-mediated transformation. Northern blot analysis verified the BjCAT3 was expressed at high level in different transgenic lines. In morphological observation, we found that seedlings from transgenic tobacco plants grew better and showed longer root length in the presence of Cd versus wild-type (WT) seedlings. Under 100 μM Cd stress, WT plants became chlorotic and almost dead while transgenic tobacco plants still remained green and phenotypically normal. The CAT activity of transgenic T1 generations was approximately two-fold higher than that of WT plants. In WT, endogenous CAT activity is rapidly reduced as a result of 200 μM CdCl2 exposure. Compared with WT plants, lower level of Cd-induced H2O2 accumulation and cell death were detected in roots of transgenic plants with high level of CAT activity. All our findings strongly support that overexpressing BjCAT3 in tobacco could enhance the tolerance under Cd stress.