Investigation of the protective role of hydrogen peroxide pretreatment in colza (Brassica napus L.) seedlings exposed to chromium stress

In this research, the effects of hydrogen peroxide (200 µM H2O2 for 24 h) pretreatment on the seedling growth, Cr accumulation, photosynthetic pigment content, thiol content, lipid peroxidation, activities of some antioxidant enzymes [superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (POD) and catalase (CAT)] and expression level of metallothionein protein 1 gene (BnMP1) were investigated on hydroponically grown canola (Brassica napus L. cv. Süzer) seedlings exposed to Cr(VI) stress (50 µM potassium dichromate) for 1 and 7 days. Cr(VI) stress decreased fresh and dry weights of canola seedlings. The reductions in seedling growth were accompanied by increased lipid peroxidation and decreased photosynthetic pigment content in leaf tissues. Hydrogen peroxide pretreatment, however, significantly enhanced plant growth parameters and led to the reduction of lipid peroxidation level and enhance of photosynthetic pigments content. On the other hand, H2O2 pretreatment increased Cr accumulation in aerial parts of canola seedlings. Cr(VI) stress increased thiol content in the leaf tissues of canola seedlings. However, H2O2 pretreatment led to further enhance in the thiol content at the 7th day of Cr(VI) exposure. Cr(VI) stress caused alterations in the activities of antioxidant enzymes such as SOD, APX, POD and CAT in the leaf tissues of canola seedlings. Under Cr(VI) stress, SOD and POD activities increased, whereas APX and CAT activities decreased. The SOD and CAT activities remained unaffected due to H2O2 pretreatment, while activities of APX and POD were significantly promoted in the Cr(VI)-stressed seedlings. In real-time quantitative PCR analysis, the expression level of BnMP1 gene was increased at 1 day after treatment (DAT), whereas it was decreased at 7 DAT in Cr(VI)-stressed seedlings. At 1 DAT, pretreatment of H2O2 reduced the expression of BnMP1 mRNA compared to Cr(VI) stress alone, but this effect was not significant. At 7 DAT, H2O2 pretreatment alleviated the Cr(VI) stress-induced decrease in the expression of BnMP1 mRNA. These results suggest that exogenous H2O2 pretreatment may probably improve the tolerance of the plant to the Cr(VI) toxicity. Cr(VI) tolerance may result from an enhanced defense system depend on H2O2 pretreatment. Anahtar Kelimeler: Brassica napus L., Cr(VI), H2O2 ön uygulaması, Antioksidant savunma sistemi, Metallotiyonein