PROMOTIVE AND INHIBITORY EFFECTS OF DIVERSE ARABINOGALACTAN PROTEINS ON DAUCUS-CAROTA L. SOMATIC EMBRYOGENESIS

Secreted arabinogalactan proteins (AGPs) isolated on the basis of spec ific epitopes, have been reported that can either enhance(ZUM18 AGP fr action) or inhibit (ZUM15 AGP fraction) carrot (Daucus carota L.) soma tic embryo development (Kreuger and van Hoist, 1995, Planta 197: 135-1 41). Here, we report that addition of the ZUM18 AGP fraction to differ ent size-fractionated cell populations isolated from embryogenic carro t suspension cultures does not show a significant effect on the freque ncy and the morphology of the somatic embryos produced. An AGP fractio n containing the JIM8 epitope showed an inhibitory effect on the frequ ency of somatic embryo development from single cells. Addition of carr ot-seed AGPs to non-embryogenic cell suspensions did not directly prom ote embryogenic competence in the suspension culture. Only after enric hment for cell clusters and removal of most of the single cells was an increase in embryogenic competence observed. These results indicate t hat cell type composition in suspension cultures is important for eval uating the effect of exogenous AGPs.