Stomatal development and patterning in Arabidopsis leaves

The functional unit for gas exchange between plants and the atmosphere is t he stomatal complex, an epidermal structure composed of two guard cells, wh ich delimit a stomatal pore, and their subsidiary cells. In the present wor k, we define the basic structural unit formed in Arabidopsis thaliana durin g leaf development, the anisocytic stomatal complex. We perform a cell line age analysis by transposon excision founding that at least a small percenta ge of stomatal complexes are unequivocally non-clonal. We also describe the three-dimensional pattern of stomata in the Arabidopsis leaf. In the epide rmal plane, subsidiary cells of most stomatal complexes contact the subsidi ary cells of immediately adjacent complexes. This minimal distance between stomatal complexes allows each stoma to be circled by a full complement of subsidiary cells, with which guard cells can exchange water and ions in ord er to open or to close the pore, In the radial plane, stomata (and their pr ecursors, the meristemoids) are located at the junctions of several mesophy ll cells. This meristemoid patterning may be a consequence of signals that operate along the radial axis of the leaf, which establish meristemoid diff erentiation precisely at these places. Since stomatal development is basipe tal, these radially propagated signals may be transmitted in the axial dire ction, thus guiding stomatal development through the basal end of the leaf.