Dual Pathways for Auxin Regulation of Cell Division and Expansion
Auxins are a class of plant growth regulators acting as a morphogen to direct two competing cellular actions depending on the concentration (Chen 2001). At a low auxin concentration, cells arrest at G1 and expand while at a slightly higher concentration, cells proceed to G2/M and divide, followed by minimal expansion to recharge the meristematic cell volume (Fig. 1A–C). Perhaps the first evidence for this idea was made using BY-2 cells in culture (Hasezawa and Syono 1983). Hasezawa and Syono scored the number of elongated cells and dividing cells at different concentrations of auxin and found that approx. 0.1 μM naphthaleneacetic acid (NAA) was optimal for elongation and approx. 5 μM NAA was optimal for division. The simplest model to explain this phenomenology is one having two auxin receptors. A high affinity receptor mediates auxin regulation of cell expansion while a low affinity receptor mediates auxin regulation of division (Fig. 1D). Supporting evidence for a dual auxin pathway using BY-2 cells is discussed further below.
KeywordsCell Elongation Auxin Signaling Auxin Receptor Dual Pathway Auxin Signaling Pathway
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