Importance of arabinogalactan proteins for the development of somatic embryos of Norway spruce (Picea abies)

The morphology of somatic embryos of Norway spruce ( Picea abies ) varies among different cell lines, from less developed somatic embryos with small embryonic regions (group B) to well developed embryos with large embryonic regions (group A). Only well developed somatic embryos will undergo a maturation process after a treatment with ABA and develop into mature somatic embryos, which is required for plant regeneration. We have previously shown that the presence of specific extracellular proteins can be correlated with the morphology of the somatic embryos. In the present study we show that extracellular proteins concentrated from group A cell lines can stimulate group B embryos to develop further and that seed extract can stably convert B embryos into A embryos. The arabinogalactan protein (AGP) fraction of the extracellular proteins and of the seed extract was shown to be an active component for stimulating B embryos to develop further. Furthermore, the amount and type of extracellular AGPs, as detected with β-glucosyl Yariv reagent and monoclonal antibodies, varied among different types of tissues and cell lines. The data show that development of somatic embryos in Norway spruce is associated with particular extracellular AGPs, which have a regulatory function.