Gene-expression programs in embryogenic and non-embryogenic carrot cultures.

Somatic embryogenesis can be synchronized by enriching carrot (Daucus carota L.) suspension cultures for small, dense clusters of cells termed proembryogenic masses (PEMs). Gene-expression programs of PEMs were compared with those of embryonic and mature tissues by in-vitro translation of representative mRNA populations and by nucleic-acid hybridization. Analysis of invitro-translated polypeptides by two-dimensional polyacrylamide gel electrophoresis revealed striking similarities between the mRNA populations of PEM and torpedo-stage embryos; substantial differences, however, were observed when in-vitro translation products of PEMs and torpedo embryos were compared with those of hypocotyls and leaves. Northern blots of RNA isolated from PEMs, staged embryos, and mature carrot tissues were hybridized with cDNA probes for Dc3, Dc5 and Dc13; these cDNA recombinants represent mRNAs that are regulated during carrot somatic embryogenesis. The pattern of expression of these embryo-regulated transcripts was similar in PEMs and somatic embryos but differed in other carrot tissues. These results indicate that many of the molecular processes of embryogenesis are already established in PEMs in the presence of auxin. Additional experiments indicate the utility of Dc3 as a molecular marker for the acquisition of embryogenic potential.