Abstract: Auxin transport inhibitor was used to explore whether auxin mediates modification of cadmium (Cd) toxicity by alginate oligosaccharides (AOS) in rice (Oryza sativa L.),from the view of the growth and antioxidant metabolism.The results showed that Cd stress significantly inhibited the growth of rice seedlings.The seedling length,aboveground biomass and belowground biomass were reduced to different degrees.Under the condition of Cd stress,AOS pretreatment significantly improved the activities of superoxide dismutase (SOD),peroxidase (POD) and ascorbate peroxidase (APX) in rice,and reduced O₂^·- production rate.These changes resulted in the increases of SOD/O₂^·-, SOD/POD,SOD/catalase (CAT) and POD/O₂^·- and the decrease of malondialdehyde content.Seedling length,root length and biomass increased to some extent,but H₂O₂ had a certain accumulation in rice.After auxin signal was blocked,the ameliorating effects of AOS pretreatment (Cd+AOS+Y) on Cd stress was weakened in rice.Compared with the treatments of non-blocked auxin signal (Cd+AOS),growth indicators (such as seedling length,root length) and the activities of antioxidant enzymes was reduced;After adding exogenous auxin (Cd+AOS+Y+NAA),various indicators had been improved in different extent.These results preliminarily showed that auxin mediated the regulation of AOS on rice resistance to Cd stress.

Key words: auxin, alginate oligosaccharides, rice(Oryza sativa L.), cadmium (Cd) stress