Promotive and inhibitory effects of diverse arabinogalactan proteins on Daucus carota L. somatic embryogenesis

Secreted arabinogalactan proteins (AGPs) isolated on the basis of specific epitopes, have been reported that can either enhance(ZUM18 AGP fraction) or inhibit (ZUM15 AGP fraction) carrot (Daucus carota L.) somatic embryo development (Kreuger and van Hoist, 1995, Planta 197: 135-141). Here, we report that addition of the ZUM18 AGP fraction to different size-fractionated cell populations isolated from embryogenic carrot suspension cultures does not show a significant effect on the frequency and the morphology of the somatic embryos produced. An AGP fraction containing the JIM8 epitope showed an inhibitory effect on the frequency of somatic embryo development from single cells. Addition of carrot-seed AGPs to non-embryogenic cell suspensions did not directly promote embryogenic competence in the suspension culture. Only after enrichment for cell clusters and removal of most of the single cells was an increase in embryogenic competence observed. These results indicate that cell type composition in suspension cultures is important for evaluating the effect of exogenous AGPs.