XVI International Botanical Congess

Shoot development in cormophytes is characterized by spatially restricted zones where organs become initiated. The capacity of the shoot apex to establish new organs can be perpetuated at the margins of leaf primordia. Both the initiation of leaves from the shoot apex flanks and the initiation of leaflets and serratures from the margins of growing leaves involve a rhythm of meristem enlargement, followed by fractionation and establishment of a new growth axis. Organ formation is often equated with meristem activity, although e.g. intercalary meristems do not show organogenesis. Blastozones designate organogenetic competent regions within the shoot. A common developmental program for organogenesis in the apical blastozone of the shoot tip and marginal blastozones of leaves is supported by expression patterns and function of certain transcription factors, e.g. class 1 knox genes.