Effects of ABA on secondary embryogenesis from somatic embryos induced from inflorescence culture ofAralia cordata Thunb

In order to investigate the effect of ABA on secondary embryogenesis from somatic embryos inAralia cordata Thunb., embryogenic callus and somatic embryos were induced from inflorescence on solid MS basal medium supplemented with 1.5 mg/L 2,4-D after eight weeks without subculture. For mass production of somatic embryos, embryogenic cell clumps were maintained in liquid MS medium supplemented with 1.0 mg/L 2,4-D, and then transferred to 2, 4-D-free medium. When developing embryos at various stages were cultured separately in liquid medium with ABA (0 to 2.0 mg/L) for three weeks, and then cultured in ABA-free liquid medium for two weeks, torpedo-shaped embryos exhibited secondary embryogenesis of 65.9% in only 0.2 mg/L ABA pretreatment. Cotyledonary embryos in cultures by 0.2, 0.5 and 1.0 mg/L ABA pretreatment also exhibited secondary embryogenesis (73%, 9.4% and 6.0%, respectively). However, globular and heart-shaped somatic embryos treated with ABA did not form secondary embryos on their hypocotyl surfaces. When cotyledonary embryos were cultured in ABA-free medium or 0.2 mg/L ABA treated medium for three weeks, and then in ABA-free liquid medium for 6 weeks, the germination frequency was lower in medium with 0.2 mg/L ABA (45.9%) than in hormone-free medium (56.8%). This result seems to be related to the high frequency of secondary embryogenesis. It is suggested that secondary embryogenesis by ABA application depends upon the stage of embryo cultured and the ABA concentration.