In order to explore the response mechanism of Brassica campestris to the Cd2+

Pb2+ single and combined stress (Cd2+—Pb2+)

a culture room experiment was conducted

where the Brassica campestris seedlings were treated with different concentrations of Cd2+ and Pb2+. The biomass

the content of antioxidant defense enzyme activities [i.e.

peroxidase (POD)

superoxide dismutase (SOD)

catalase (CAT) activities] and malondialdehyde (MDA)

and the enrichment of heavy metal ions were measured. In addition

the metallothionein gene BcMT2a which was associated with heavy metal enrichment was cloned and its expression was also analyzed. The results were as follows: except the low concentration of Cd2+ (10 mg/L)

which could promote the root length and aboveground growth of Brassica campestris

both the Cd2+ and Pb2+ single and combined stress could inhibit the development of root length and the growth of aboveground of Brassica campestris. And with the increasing concentrations of heavy metal ion

the inhibition effects were gradually strengthened. The order of inhibition effects of heavy metal ions was Pb2+＞Cd2+—Pb2+＞Cd2+. In the antioxidant enzyme system

POD and SOD activity were higher

and showed a trend of increasing first and decreasing then

as well as CAT activity. MDA content reached the maximum when Cd2+ concentration was 40 mg/L. The order of heavy metal ions accumulation in the organs of Brassica campestris was root＞stem＞leaf. The protein encoded by BcMT2a gene is a hydrophathy and mutant protein predominantly present in the nucleus. In a certain concentration rage

the relative expression of BcMT2a increased with the increase of Cd2+

Pb2+ and both combined concentrations

and the trend of relative expression was consistent with the result of the antioxidant enzyme system. These findings indicate that the antioxidant enzyme system and BcMT2a have a clear response under the different concentrations of Cd2+

Pb2+ and Cd2+—Pb2+ in Brassica campestris

and they can increase the tolerance of Brassica campestris to Cd2+ and Pb2+ stress.