Changes in the geometry of the apical meristem and concomitant changes in cell wall properties during photoperiodic induction of flowering in Chenopodium rubrum.

•  A putative role for local forces at the surface of the apical meristem for plant organogenesis has been postulated in various studies. To correlate changes in morphogenesis to altered local forces, we followed the geometry of the apical meristem during photoperiodic flower induction in Chenopodium rubrum. •  The shape of the apical meristem was determined using cryo-scanning electron microscopy. Cell wall properties on the surface of the dome were visualized using uplight polarization microscopy. •  A subtle depression at the summit of the apical dome, typical for the vegetative state, became rounded during the early phase of flower induction. The observed changes were quantified as an increase in the ratio of height to diameter of the dome. In parallel, the properties of cell walls on the surface of the dome changed. •  The changes in geometry of the apical meristem were attributed to water movement in the meristem paralleled by a change in cell wall properties at the top of the dome. The results support the hypothesis that local changes in surface tension precede initiation of organ primordia.