Abstract: It is well known that application of 5-aminolevulinic acid (ALA) could promote the plant growth under abiotic stress in oilseed rape (Brassica napus L.).  However, the specifics of its physiological and ultrastructural regulation under herbicide stress conditions are poorly understood.  In the present study, alleviating role of ALA in B. napus was investigated under four levels of herbicide propyl 4-(2-(4,6-dimethoxypyrimidin-2-yloxy) benzylamino) benzoate (ZJ0273) (0, 100, 200 and
500 mg L^–1) with or without 1 mg L^–1 ALA treated for 48 or 72 h.  Results showed that after 48 h of herbicide stress, the growth of rape seedlings was significantly inhibited with the successive increases of the ZJ0273 concentrations from 0 to 500 mg L^–1, but this inhibition was obviously alleviated by exogenous application of ALA.  However, when treatment time prolonged to 72 h, the recovery effects of ALA could not be evaluated due to the death of plants treated with the highest concentration of ZJ0273 (500 mg L^-1).  Further, the root oxidizability and activities of antioxidant enzymes (superoxide dismutase, peroxidase and ascorbate peroxidase) were dramatically enhanced by the application of 1 mg L^–1 ALA under herbicide stress.  Therefore, plants treated with ALA dynamically modulated their antioxidant defenses to reduce reactive oxygen species (ROS) accumulation and malondialdehyde (MDA) content induced by herbicide stress.  Additionally, exogenously applied ALA improved the ultrastructure’s of chloroplast, mitochondria and nucleus, and induced the production of stress proteins.  Our results suggest that ALA could be considered as a potential plant growth regulator for the improvement of herbicide tolerance through alleviation of the physiological and ultrastructural changes induced by the herbicide in crop production.

Key words: Brassica napus L. ,  ALA ,  ZJ0273 ,  plant growth ,  antioxidant enzyme activities ,  ultrastructure ,  two-dimensional gel electrophoresis (2-DE)