Experimental Morphology and Morphogenesis Then and Now: A Symposium in Memory of Elizabeth G. Cutter
Jernstedt, Judy .
Shoot apical meristems as clone generators: developmental implications.
The diversity of shoot apical meristem (SAM) organization in vascular plants ranges from the single inverted pyramidal (often tetrahedral) initial cell (apical cell) of many ferns and some lycophytes, to multiple surface initial cells of many other ferns, the homosporous lycophytes, and most gymnospermous seed plants, to the stratified SAMs of angiosperms. Ambiguity exists about SAM organization in the gnetophytes, and confounding factors in investigations of all taxa include stage of the plastochron, dormant shoots vs. actively growing shoots, stage of branching in dichotomously branching taxa, developmental age (juvenile vs.adult), and surface views of the SAM vs. integrated 3-D images. Many studies have focused on comparative cytological and anatomical details of different SAM types, such as the shape of the single apical cell, staining characteristics of individual cells and/or populations of cells, planes of cell division, and location and frequency of mitotic divisions. A recurring theme of SAM activity in those apices with multiple surface initials is the stochastic nature of initial cells. This may be a consequence of the limited number of mitotic divisions a given initial cell is “permitted” before a neighbor (often a mitotic sister cell) takes over as an initial. Such replacement of initial cells is reminiscent of P. Lu’s work showing the transient nature of the single apical cell in a dichotomizing axis of Selaginella martensii, where the new apical cell of each new diverging shoot is selected from apparently indistinguishable cells in a new growth center within a merophyte (clone) from the original apical cell. Work with collaborators S. Little, M. Christianson, and B. Zagorska-Marek provides evidence that each initial cell in apices with multiple surface initials, such as Ginkgo biloba, in turn “launches” its (at first) single-celled clone, which subsequently increases in cell number, to form a 3-dimensional wedge or slab of “tissue.” Successive wedges are nested together and sequentially superimposed upon their predecessors to construct the growing shoot tip.
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1 - University Of California Davis, Department Of Plant Sciences, Davis, CA, 95616-8515, USA, 530/752-7166
Shoot Apical Meristem
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 11:30 AM