In plants, stem cells are maintained in structures known as meristems, which produce plant organs. Floral meristems (FMs) produce one flower consisting of a finite number of organs such as stamens and carpels, which are formed sequentially from primordia. So far, the real-time cellular dynamics of floral organ primordia initiation and floral meristem termination (FMT) have not been well described. Now, Ya Min, Stephanie Conway and Elena Kramer use live imaging of an in vitro culture of Aquilegia coerulea (from the buttercup family) to describe growth dynamics during late stages of flower development and FMT. They find that both cell expansion and cell division rate are higher in the peripheral meristem than in the centre during stamen, staminode and carpel development. Furthermore, they observe that the initial outgrowth of all the organ primordia is characterised by high rates of growth on the abaxial side, which faces away from the stem, followed by more isotropic expansion. The authors also identify an increase in cell division during carpel primordia initiation, which is coincident with the onset of FMT. Together, these data describe the dynamics during FM transitions in a complex flower and offer insights in the role of cell division in carpel formation.
