Signalling in plant embryos during the establishment of the polar axis

In brown algae fertilization takes place free from surrounding tissue layer s. The cytoskeleton and transmembrane links to the cell wall are involved i n establishing and stabilizing the polar axis and in determining the fate o f cells in the early embryo. In seed plants, the egg cell and zygote exhibi t apical-basal polarity. Mutant studies suggest that axes of polarity of th e early embryo depend on signalling between the apical and basal compartmen ts, possibly involving auxin. Development of somatic cells into plant embry os involves extracellular matrix-derived arabinogalactan proteins. This sug gests a role for the cell wall in plant embryogenesis.