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 Astragalus adsurgens Pall. The highest frequency of somatic embryogenesis occurred at 150 mu mol/l SA. Enhanced somatic embryogenesis by SA was accompanied by an increase in the endogenous H2O2 level as compared with controls. This increased endogenous H2O2 level was related to the inhibition of the activities of ascorbate peroxidase (APX) and catalase (CAT). Although the promoting effect of exogenous H2O2 was significantly lower than that of exogenous SA on the development of somatic embryos, the pre-treatment of callus with dimethylthiourea (a trap for H2O2) significantly inhibited somatic embryogenesis, even if callus was cultured on the differentiation medium supplemented with 150 mu mol/l SA, suggesting that the endogenous H2O2 was required for SA-enhanced somatic embryogenesis. The significance of the interaction of SA, H2O2 and H2O2-metabolizing enzymes during somatic embryogenesis is discussed, and the possible relationship between SA-enhanced somatic embryogenesis and SA-induced pathogenesis-related proteins is proposed. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.