First stage of Arabidopsis embryogenesis:
Arabidopsis embryogenesis initiates with zygotic stage immediately following double fertilization distinguished by zygote elongation along apical-basal axis, polarization of vacuole and mitochondria, and asymmetric division into apical and basal daughters. This initial stage precedes quadrant stage four-celled embryo, octant, dermatogen, globular, heart, torpedo, mature embryo stages. Zygotic stage encompasses activation of embryonic transcriptome after extensive chromatin reprogramming involving WOX family, auxin signaling, and epigenetic regulators. Therefore it represents earliest morphologically recognizable stage establishing apical-basal polarity foundation for all subsequent patterning and tissue differentiation events during seed formation in planta.
Ref: Jürgens et al., Annu Rev Plant Biol 1994: first stage of Arabidopsis embryogenesis is zygotic stage with asymmetric division.