Effect Of Exogenous Salicylic Acid On Toxicity Of Rapeseed(Brassica Napus L.)under Napropamide Stress

The herbicide napropamide is widely used for weeding out most annual monocotyledon grasses and many broad leaf weeds such as lamb-quarter, wide amaranth in much agricultural cultivation. However, the side effect of napropamide as contaminants on crops is unknown. Salicylic acid (SA) is one of the most important natural plant growth regulators and signal molecules. Salicylic acid is an important part in regulating local defense and induction of systemic resistance response in pathogen attacked plants. In this study, four treatments were set up:control (CK),0.1mM salicylic acid (SA),8mg L-1napropamide(N),0.1mM salicylic acid and8mg L-1napropamide(SA+N).We investigated the effects of exogenous salicylic acid in rapeseed (Brassica napus) on growth, antioxidant response and the herbicide napropamide accumulation under napropamide stress.The results show that treatment with napropamide only inhibited growth and depress the biomass of rapeseed, compared to the controls, N treatment decreased46.1%and28.4%in roots and shoots, respectively. The simultaneous treatment of plants with0.1mM SA significantly improved the napropamide-inhibited growth. As compared to8mg L"1napropamide alone, the biomass of roots and shoots increased to20.7%and18.4%. Treatment with napropamide induced the accumulation of O2-and H2O2in leaves and resulted in the peroxidation of plasma membrane lipids in the plant. The accumulation of TBARS observed in8mg L-1napropamide treatment increased71.2%and132.2%in roots and leaves, respectively. The treatment of plants with0.1mM SA and8mg L"1napropamide, the level of TBARS decreased to84.3%(in roots) and79.2%(in leaves) of the napropamide alone.To protect the ROS-induced oxidative damage, plant cells have developed multiple defense systems, including antioxidant enzymes, such as SOD, CAT, APX GPOX, GST and GR. SA caused a decrease in napropamide-induced SOD CAT and APX activities, but an increased in POD GST and GR activities. To get an insight into the change of enzymes activities, a non-denaturing polyacrylamide gel electrophoresis (PAGE) for SOD, POD and CAT activities was performed. These results suggested that exogenous SA could alleviate oxidative damage in rapeseed subjected to napropamide stress.The accumulation of napropamide on rapeseed plant was studied. The result showed that napropamide accumulation in leaf and root of rapeseed plant was decreased significantly in presence of SA, suggesting a protective ability of SA against napropamide damage to rapeseed.