The morphogenetic rôle of apical meristems: fundamental aspects (illustrated by means of the shoot apical meristem)

Role for the shoot apical meristem in the specification of juvenile leaf identity inArabidopsis

“…The extent to which the SAM autonomously regulates shoot development-as opposed to simply responding to regulatory factors produced by organs and tissues outside the SAM-is a classic question in plant development. Classically, vegetative phase change was thought to result from changes in the developmental identity of the SAM; indeed, the apparent stability of the juvenile and adult phases provided some of the first evidence that cells in the SAM can become determined for specific developmental fates (14,15,40). It is also clear that the timing of vegetative phase change can be influenced by various environmental factors and by organs/tissues external to the SAM.…”

“…While there has been recent progress in elucidating the molecular mechanisms that control the temporal decline of miR156 expression (8)(9)(10)(11)(12)(13), how expression of the miR156-SPL pathway and the process of VPC are coordinated across the shoot apex remains unknown. It has long been thought that the identity of a shoot is determined by the maturation state of the SAM (14,15). A regulatory role for the SAM is further supported by the phenotypes of plants that have reduced meristems and that immediately produce leaves with adult traits, such as wuschel (wus) and paused (psd) mutants (16,17).…”

Temporal regulation of vegetative phase change in plants

“…Whether the shoot apical meristem (SAM) controls the timing of vegetative phase change autonomously, or simply responds to external cues, is a classic question in plant biology 195,196 . It was traditionally thought that the juvenile-to-adult transition is regulated within the SAM 197 , but more recent work has demonstrated that pre-existing leaves promote both the initiation and the maintenance of the adult phase.…”