Figure 7.

Auxin flux and auxin perception maxima during embryogenesis.

In the early stages of embryogenesis, localization of the PIN7 auxin efflux facilitator (cyan) to the apical membranes of basal cell and subsequently suspensor cells appears to drive auxin flux (arrows) upwards. A weak DR-5 marked auxin perception maximum (light purple) suggestive of auxin accumulation is seen in the apical parts of the developing embryo up to and including the dermatogen stage. During the globular stage PIN1 (dark blue) localization in the basal membranes of the inner cells of the embryo is associated with a switch in the apparent direction of auxin flux to apical — basal. At this time PIN7 is now seen concentrated in the basal membranes of the hypophysis and suspensor cells. A stronger auxin perception maximum (purple) also appears in the hypophysis and apical cells of the suspensor, which becomes restricted to the daughter cells of the hypophysis. PIN1 distribution in the cells of the L1 layer is associated with the generation of auxin perception maxima at the positions of incipient cotyledon initiation. Figure redrawn from Jenik et al. (2007) with permission from Annual Reviews.