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. Author manuscript; available in PMC: 2009 Aug 1.
Published in final edited form as: Curr Opin Genet Dev. 2008 Jul 9;18(4):354–361. doi: 10.1016/j.gde.2008.05.001

Figure 3.

Figure 3

Simplified schematic of the efflux routes of auxin resembling an inverted fountain in the Arabidopsis primary root (7 days old) as viewed by laser confocal microscopy under 25X magnification. Auxin is thought to be transported from the shoot downward to the root tip via PIN carriers in the central cell layers of the root. Once auxin reaches the tip it is believed to be directed outward to the outer cell layers by different PIN carriers. It is then thought to be transported upward toward the shoot by still other PIN carriers. Some of this auxin may also be recycled from the outer root layers back into the inner ones to provide a ‘battery’ like mechanism that maintains auxin levels within the root tip. The meristematic (white bar) and elongation (light blue bar) zones are shown. Cell walls are visible in red from propidium iodide staining.