Synthetic versions like 2,4-D acetic acid are used as selective herbicides,such as the defoliating Agent Orange, and one natural example is indole-3-acetic acid.
The flavinoid Quercetin inhibits transport of these compounds, which can inhibit gene expression by binding to TIR1 in the nucleus. Their major effect stems from causing cells to actively transport hydrogen ions out of the cell, acidifying the local extracellular medium, activating (*) expansins in the cell wall.  Their movement is regulated by PIN proteins in a process called polar transport. Other effects mediated by these compounds include phototropism and apical dominance.  Synthetic versions like 2,4-D acetic acid are used as selective herbicides,such as the defoliating Agent Orange, and one natural example is indole-3-acetic acid. For 10 point, name this plant hormone that promotes growth.
The flavinoid Quercetin inhibits transport of these compounds, which can inhibit gene expression by binding to TIR1 in the nucleus.
{Auxins} [accept {Indole}-{3}-{acetic acid} or {IAA} until mentioned]