Analysis of Surface Growth in the Conifer Shoot Apical Meristem

Abstract

Premise of research. The structure and organization of the conifer shoot apical meristem was investigated using confocal microscopy of whole-mount shoot apical meristems. This article presents detailed surface and internal patterns that provide an informative and comparative model of meristem growth that is able to account for the diversity and variation of conifer meristem form.Methodology. Confocal microscopy; light microscopy.Pivotal results. On the surface of the meristem, two zones with distinct cell division patterns were recognized. The first is the summit zone that covers the apex of the meristem dome, and the second is the peripheral zone that covers the flanks of the meristem. In the summit zone, successive anticlinal cell divisions are perpendicular to each other and produce isotropic growth. In the peripheral zone, surface cells divide with repetitive transverse divisions to form long axial chains that create packets with anisotropic growth. Only cells in the summit zone divide periclinally to contribute daughter cells to the underlying tissue. Those meristems with a small number of cells in the summit zone have a correspondingly small number of periclinal divisions of apical initial cells. Those meristems with larger summit zones and many wedge-shaped packets have a larger number of apical initials dividing periclinally.Conclusions. Conifer meristems have consistent cell division patterns that define the summit and peripheral zones. Apical initials are transient, and their number varies between meristems, depending on the size of the summit zone.