Abstract: We investigated the regulation of α-naphthaleneacetic acid (NAA) on cold resistance of Brassica campestris variety ‘Longyou 6’ seedlings by measuring parameters, including reactive oxygen (H₂O₂ and O₂^-_·) content, antioxidant enzyme activities, contents of malondialdehyde (MDA), soluble sugar, proline and chlorophyll, the expression level of antioxidant enzymes genes (APX, CAT, GR,SOD), RbohA-F, MAPK3/4/6, CBF and ICE1genes. Six treatments were applied to both leave and root tissues: 4 ℃, NAA+4 ℃, NAA+4 ℃+DPI (NADPH oxidase inhibitor), NAA+4 ℃+DMTU (H₂O₂ scavenger), NAA+4 ℃+U0126 (MAPK inhibitor), and NAA+4 ℃+Tungstate (NO production inhibitor). The results showed that cell viability, H₂O₂ and O₂^-_· contents, and MDA content in leaves decreased under NAA+4 ℃ treatment compared with 4 ℃ treatment. Antioxidant enzymes (CAT, SOD, APX and POD) in roots as well as soluble sugar, proline, chlorophyll contents and related genes expression in leaves increased. These results indicated thatBrassica campestris seedlings treated with α-naphthaleneacetic acid could significantly improve their antioxidant capacity, photosynthetic capacity, and the expression of related genes, and consequently enhance their cold resistance. Compared with NAA+4 ℃ treatment, chlorophyll content, antioxidant enzymes genes (APX, CAT, GR, SOD), RbohA-F,MAPK3/4/6, CBF andICE1 decreased in seedlings treated with NAA+4 ℃+inhibitors (DPI, DMTU, U0126 and Tungstate) to different extents, indicating that H₂O₂ and NO signaling molecules, NADPH oxidase and MAP kinase cascades are all involved in the regulation of αnaphthaleneacetic acid on cold resistance of Brassica campestris seedlings.

Key words: shallow lake, regional heterogeneity., altitude, cladocera, nutrient level