Figure 1. Schematic representation of the vascular bundle structure.

The shoot vascular bundles of Arabidopsis are considered as an array of three compartments in the position of procambial (pc) and young xylem (xy) and phloem (ph) cells. Each cell type is characterized by, among other things, the presence of one or two proteins that we will consider cell-type markers: VND and ASL in the xylem, WOX4 in the procambium, and APL in the phloem. The microphotograph is showing the cross section of living (non-fixed) inflorescence stem of Arabidopsis stained with toluidine blue as described in [15].