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doi: 10.1242/10.1242/jcs.00406

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Stem cell regulation in the shoot meristem

¹ Institute of Plant Biology, University of Zürich, Zollikerstraße 107, 8008 Zürich, Switzerland
² Institute of Biologie III, University of Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany

View larger version (32K): [in a new window]   Fig. 1. Mechanisms of stem cell divisions. If individual stem cells in a niche are differently marked (color coded green or white) the mechanism of division can be assessed (for clarity, only stem cells but not differentiating cells are depicted). (A) If regulated at the single cell level, each stem cell division is strictly asymmetric to give rise to an new stem cell and a differentiating cell (shaded arrows, cells not shown). The distribution of genetic sectors does not change. (B) If regulated in a population mode, symmetric and asymmetric divisions occur. Owing to symmetric divisions genetic sectors can enlarge at the expense of others. See text for details.

View larger version (56K): [in a new window]   Fig. 2. Organization of the Arabidopsis shoot meristem. (Left) An Arabidopsis seedling is shown from a top view. (Right) A longitudinal section through the shoot apex is shown (figure adapted from Laux and Schoof, 1997). The approximate outlines of the central zone (CZ), peripheral zone (PZ) and rib zone (RZ) are given. For details, see text.

View larger version (37K): [in a new window]   Fig. 3. Isolation of shoot meristem stem cell mutants in Arabidopsis. In this model of shoot meristem initiation, the first leaf primordia (green) arise before the central cells appear to be specified (red), whereas subsequent leaves are derived from the stem cells. Mutations affecting partitioning of the shoot meristem primordium could result in an altered size of the stem cell region, represented by stm (with fused organ primordia, arrow) and clv (with an increased meristem, arrow) mutants. Mutations affecting stem cell specification would result in altered cells in the center but normal first leaves, represented by a wus seedling.

View larger version (33K): [in a new window]   Fig. 4. Model for the regulation of stem cells in the Arabidopsis shoot meristem. The CZ comprises both the stem cells (blue) and the OC (red), expressing CLV3 and WUS, respectively (insets: in situ hybridizations). WUS activity in the OC results in specification of stem cell identity in the three outermost cell layers, which in turn signal back by CLV3, restricting the WUS expression domain. Note that the expression domains in this figure are estimated based on comparison of separate experiments and not on simultaneous detection of the genes.

View larger version (10K): [in a new window]   Fig. 5. Initiation of shoot meristem stem cells in the Arabidopsis embryo. An OC precursor cell lineage expressing WUS (red) is established in the four subepidermal cells of the 16-cell embryo. As judged from CLV3 expression (blue), stem cells are induced in heart stage embryos. The thick line indicates the clonal boundary between apical and basal derivatives of the 8-cell embryo (figure adapted from Schrick and Laux, 2000).

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