Vegetative Shoot Meristems

Abstract

The shoot apical meristem (SAM) is responsible for the indeterminate growth of the maize shoot. Formed during embryogenesis, the SAM consists of a pool of stem cells that divide to give rise to daughter cells that either maintain stem cell fate or are incorporated into leaf primordia, axillary shoot meristems or the growing stem tissues. Classical studies over the past century have revealed the cellular organization of the SAM, its ability to respond to systemic signals from distant organs, and behavior and fates of cells in this small but essential structure. More recently, we have started to understand molecular mechanisms of SAM function, an insight that has only been possible through forward genetic analysis. Several pathways for meristem maintenance and proliferation control are now known, however an integrated model of how the meristem functions awaits further genetic and genomic analysis. As the SAM is formed during embryogenesis and persists through the inflorescence phase, and its activity is intimately integrated with leaf initiation, readers are encouraged to also consult the chapters on Maize Embryogenesis by Wolfgang Werr, Axial patterning of the maize leaf by Toshi Foster and Marja Timmermans, Floral Transition in Maize by Joe Colasanti and Mike Muszynski and Inflorescences by Robert Schmidt and Erik Vollbrecht.