Figure 1.

Glandular trichome initiation and development, a process with many unknowns. A differentiating protodermal cell integrates both environmental and endogenous signals. Such signal integration results in the selection of a pool of trichome cell precursors that will initiate a specific developmental program. In these trichome initials, cell-specific transcriptional control of gene expression and cell cycle regulation results in the onset of a controlled cell division and trichome morphogenesis program, most of which is still not so well understood in the case of glandular trichomes. It probably also involves some cell-cell signaling promoting the one cell-spacing rule, which allows a specific patterning of trichomes in the epidermis. Morphogenesis of the trichome glandular head also necessitates extensive remodeling of the cell wall. The extent of endoreduplication in glandular trichomes is still mostly uncharacterized. The illustration shows a modified confocal image of a long glandular trichome initial from N. tabacum. Chloroplasts are shown in green, propidium iodide-stained cell walls in magenta, and nuclei in cyan.