Fig. 1. Organisation of the shoot apical meristem, and schematic representation of the ablations performed in this study. (A) SEM micrograph of a vegetative shoot apical meristem of tomato. P₃, P₂ and P₁ indicate young primordia. P₁ is just being initiated at the flank. (B-F) Schematic representation of a meristem as in A. (B) The meristem consists of the central zone (CZ, light blue) that harbours the stem cells (dark blue) and the peripheral zone (PZ, yellow) in which organs are formed. An organising centre that expresses the marker gene LeWUS (red) induces stem cell identity in the above cells. Superimposed on the zonation (CZ and PZ), the meristem is organised in layers, namely the external L₁ layer, the subepidermal L₂ layer and the remaining cells, called L₃. All three layers cooperate in organ formation (arrowhead). (C) Ablation of the entire CZ. (D) Ablation of the stem cells. (E) Ablation of the L₁ layer in the CZ. (F) Ablation of the entire L₁ layer. Scale bar: 100 µm.

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