Effect of growth regulators on polyamine level of tissues during somatic embryogenesis induction in fennel (Foeniculum vulgare Miller)

When fennel (Foeniculum vulgare Miller) petiole explants were grown on an auxin-containing medium, somatic embryogenesis was induced after 3-4 weeks. The free polyamine content of tissues progressively increased during the first month of culture and then decreased. These variations mainly concerned putrescine, which was the major polyamine. The polyamine level rose proportionnally to the auxin strength and concentration. However, a high auxin level (2,4-D), or cytokinin addition to the medium (Kin or BAP), though inducing polyamine accumulation, caused an inhibition of embryogenesis induction. Polyamines also increased in non-embryogenic explants grown in vitro on a medium devoid of auxin. Thus, the acquisition by tissues of the ability to produce somatic embryos was not induced by the endogenous polyamine level variations. The discussion lays emphasis on factors liable to cause a temporary accumulation of polyamines in tissues.