Abstract:To investigate the mechanism of exogenous ABA alleviate the hyperhydricity of garlic plantlet in vitro, we studied the effects of exogenous abscisic acid (ABA), hydrogen peroxide (H2O2) and H2O2 +ABA on hyperhydricity, accumulation and localization of reactive oxygen species, and response of antioxidant system of plantlet in vitro with garlic variety ‘Ershuizao’. The results showed: (1) H2O2 aggravated hyperhydricity, the hyperhydric rate was the lowest under ABA treatment, and adding ABA into media with H2O2 alleviated hyperhydricity induced by H2O2. (2) O-·2 production rate and H2O2 content was the lowest under ABA treatment and the highest under H2O2 treatment. Adding ABA to the medium with H2O2 reduced the O-·2 production rate and H2O2 content. (3) The activities of catalase (CAT), peroxidase (POD) and ascorbate oxidase (APX) increased at the early stage during 0-8 day of H2O2 treatment, but then antioxidant enzyme activities of CAT, APX decreased and that of POD increased slowly during 8-16 day. SOD, CAT, POD, GR and APX activities increased linearly at 0-8 d under treatment of ABA and H2O2 + ABA. Activities of SOD, CAT, POD and APX under H2O2 + ABA treatment increased and were significantly higher than those of H2O2 treatment during 8-16th day. (4) The contents of ascorbic acid (AsA) and glutathione (GSH) increased at first and decreased later, were the highest under ABA treatment and the lowest under H2O2 treatment. (5) Tissue localization results showed that O-·2 and H2O2 were mainly produced in base of plantlets and tips of leaves. The accumulation of reactive oxygen species was the lowest under ABA treatment. (6) The content of malondialdehyde and membrane relative permeability under treatment of H2O2 + ABA was significant lower than that under H2O2 and control treatments. In summary, exogenous ABA can improve the antioxidant capacity of plantlets in vitro, reduce the accumulation and diffuse of reactive oxygen species, thereby inhibiting the occurrence of hyperhydricity.