A secreted peptide growth factor, phytosulfokine, acting as a stimulatory factor of carrot somatic embryo formation

Somatic embryogenesis of the carrot (Daucus carota L.) depends on a set of factors, some of which accumulate in culture medium (conditioned medium, CM ), When embryogenic cell clusters were transferred to an embryo-inducing me dium, addition of CM derived from somatic embryo culture markedly stimulate d somatic embryo formation. The active principles were purified using a sim ple bioassay system and identified to be phytosulfokines (PSKs), sulfated o ligopeptide growth factors originally isolated from a CM derived from aspar agus (Asparagus officinalis L,) mesophyll culture. Quantification studies u sing a competition ELISA system employing an anti-PSK-a polyclonal antibody showed that PSK production might be related to growth of cells, rather tha n development of somatic embryos. Thus the stimulatory effect of PSK on som atic embryo formation might be due to promotion of cell proliferation.