Effects of different NaCl concentration on the antioxidant enzymes in oilseed rape (Brassica napus L.) seedlings

The effects of salt stress on the activity of antioxidant enzymes in oilseed rape seedlings (Brassica napus L.) were studied. The results showed that the relative water content in leaves of oilseed rape seedlings was gradually decreased and the electrical conductivity was increased after 24 h under 0, 100, 150, 200, 250 and 300 mmol L-1 NaCl. The activity of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) was gradually increased under salt stress. After 24 h, the activity of POD and SOD was both maximal under 200 mmol L-1, but that of CAT was maximal under 150 mmol L-1. Subsequently, the activity of these antioxidant enzymes was all decreased. Quantitative real-time PCR analysis revealed that they were salt-inducible genes and their transcript levels were gradually increased with the increase of salt concentration. As the same as the change of POD and SOD activity, the transcript levels of POD and SOD was most abundant after 24 h treatment with 200 mmol L-1 sodium chloride, but that of CAT was most abundant under 150 mmol L-1. Therefore, these results from above indicated that the expression of POD, SOD and CAT genes was induced by salt (such as NaCl) and their activities were positively correlated with expression of their genes.