The aim of the present work was to investigate the effects of osmoconditioning on chilling injury in chilling-sensitive soybean(Glycine max(L.) Merr.Zhonghuang No.22) seeds during imbibition.Low temperatures reduced the germination rate and no seed germinated at 1℃C.Osmoconditioning of seeds at 20℃ with a polyethylene glycol-8000(PEG8000) solution at 1.5 MPa for 72 h followed by drying back to their initial moisture content(MC) reduced their chilling sensitivity.The phenylarsine oxide(PAO),an inhibitor of protein tyrosinephosphatases,was used to investigate the possible involvement of phosphorylation-dephosphorylation of Tyr residues in the plasma membrane composition and function when seeds were osmoconditioned.The results showed the germination of osmoconditioned seeds decreased significantly when PAO was added in PEG solution after chilling treatment.PAO inhibited changes in composition of plasma membrane phospholipids and fatty acid induced by osmocondition,indicated that tyrosine protein phosphorylation is involved in the regulatory mechanisms of osmocondition-responsive chilling in soybean seeds.Western blot result further indicated that osmocondition treatment improved the activity of plasma membrane H+-ATPase after chilling treatment,but this effect was abolished by PAO.The possible regulation mechanism by Tyr protein phosphorylation is discussed. The aim of the present work was to investigate the effects of osmoconditioning on chilling injury in chilling-sensitive soybean (Glycine max (L.) Merr. Zhonghuang No.22) seeds during imbibition. Low temperatures reduced the germination rate and no seed germinated at 1 ° C. C. Osmoconditioning of seeds at 20 ° C with a polyethylene glycol-8000 (PEG 8000) solution at 1.5 MPa for 72 h followed by drying back to their initial moisture content (MC) reduced their chilling sensitivity. The phenylarsine oxide (PAO), an inhibitor of protein tyrosine phosphatases, was used to investigate the possible involvement of phosphorylation-dephosphorylation of Tyr residues in the plasma membrane composition and function when seeds were osmoconditioned. The results showed the germination of osmoconditioned seeds decreased significantly when PAO was added in PEG solution after chilling treatment. PAO changes changes in composition of plasma membrane phospholipids and fatty acid induced by osmocondition, indicated that tyros ine protein phosphorylation is involved in the regulatory mechanisms of osmocondition-responsive chilling in soybean seeds. Western blot result further indicated that osmocondition treatment improved the activity of plasma membrane H + -ATPase after chilling treatment, but this effect was abolished by PAO. Possible regulation mechanism by Tyr protein phosphorylation is discussed.