SoPIN1, PIN1a and PIN1b act in concert during leaf initiation.

<p>(A) SoPIN1 acts up-the-gradient to create an auxin maximum, which is directed to the sink by PIN1b (B), and refined by PIN1a (C), both acting with-the-flux. In (C) PIN1b begins to polarize the adjoining tissue, converting the newly formed trace into a sink for new organs. Auxin concentration as inferred by DR5 is colored red, SoPIN1 green, PIN1b blue and PIN1a red. Arrows show the direction of transport and the relative polarity of the tissue.