Enhanced somatic embryogenesis by salicylic acid of Astragalus adsurgens Pall.: relationship with H2O2 production and H2O2-metabolizing enzyme activities

Salicylic acid (SA), when added to the differentiation medium below 200 mu mol/l, significantly enhanced somatic embryogenesis in callus culture of As tragalus adsurgens Pall. The highest frequency of somatic embryogenesis occ urred at 150 mu mol/l SA. Enhanced somatic embryogenesis by SA was accompan ied by an increase in the endogenous H2O2 level as compared with controls. This increased endogenous H2O2 level was related to the inhibition of the a ctivities of ascorbate peroxidase (APX) and catalase (CAT). Although the pr omoting effect of exogenous H2O2 was significantly lower than that of exoge nous SA on the development of somatic embryos, the pre-treatment of callus with dimethylthiourea (a trap for H2O2) significantly inhibited somatic emb ryogenesis, even if callus was cultured on the differentiation medium suppl emented with 150 mu mol/l SA, suggesting that the endogenous H2O2 was requi red for SA-enhanced somatic embryogenesis. The significance of the interact ion of SA, H2O2 and H2O2-metabolizing enzymes during somatic embryogenesis is discussed, and the possible relationship between SA-enhanced somatic emb ryogenesis and SA-induced pathogenesis-related proteins is proposed. (C) 20 01 Elsevier Science Ireland Ltd. All rights reserved.