The shoot apical meristem: an historical perspective1

摘要

Although much of the current investigation of shoot apical meristems is in the realm of molecular genetic analysis, it is important that previous structural and functional studies not be overlooked as essential background to these studies. Since Caspar Friedrich Wolff described the shoot apical meristem in 1759, many and varied interpretations have arisen. In the early 19th century, the apical cell was recognized in seedless vascular plants and this interpretation was extended to seed plants. However, by the 1860s, this view was replaced in seed plants by the histogen concept, which recognized meristem layers in the apical meristem giving rise to specific tissues. In 1924, the tunica-corpus interpretation of angiosperm shoot apices became widespread, the two regions being distinguished by different planes of cell division. In the 1950s, the d'attente concept appeared in France, which argued that the central region of the apex remained essentially inactive until the onset of flowering. Meanwhile, the recognition of zonation patterns in angiosperm and gymnosperm shoot apices assumed growing functional importance. Clonal analysis based on chimeras in the meristem indicated the presence of initial cells but also their replacement. Surgical experimentation and culture of excised apices in vitro stressed the autonomy of the shoot apex and its role in shoot development. Present molecular genetic analysis may help to resolve some of the persistent questions concerning the organization and functioning ofshoot apical meristems.