Plant regeneration from cultured Medicago truncatula with particular reference to abscisic acid and light treatments

Medicago truncatula (Jemalong 2HA) can be regenerated by somatic embryogenesis utilising 1-naphthalene acetic acid (NAA) and 6-benzylaminopurine (BAP). There is a requirement for both NAA and BAP for callus induction and embryo formation. There is no requirement for a drop in auxin concentration to induce embryos. Abscisic acid (ABA) when present with NAA and BAP during embryo formation at a concentration of 1 mu M, increases the number of embryos per callus. The ABA treatment stimulates embryo numbers in both light and darkness. The conversion efficiency of embryo to plant is unchanged irrespective of the presence of ABA during embryo formation, indicating that ABA does not improve the regeneration of the embryos once formed. Importantly, the presence of light in the embryo formation period causes a marked inhibition of embryo conversion.