Establishment of the apical-basal axis in multicellular plant embryos

Apical-basal polarity of multicellular plant embryos is defined originally in the zygote before the first cell division and the apical and basal daughter cells follow distinct developmental programs. Mechanisms controlling these initial embryonic steps are still poorly understood but advances both in the flowering plant Arabidopsis and the alga Fucus have lead to various models and hypotheses. These point to the positional information as a major source for patterning the early embryo. Hypotheses concerning the possible location of this positional information are reviewed and discussed.