Figure 10.

The Source and Translocation of the Leaf-Derived Signal.

An illustration modeling the translocation of the leaf-derived mobile signal. The signal originates in developing leaves (longer than 3 cm, but not leaves that are emerging at the shoot apex). Its flow is nonpolar in the leaf blade and becomes polar only in the lower midvein toward the stem (arrows mark flow orientation). The unique anatomy at the base of the petiole (blue dotted line) potentially retards the flow, which induces a local maximum (star), thereby acting as the leaf's elongation driving force. The signal flows in both directions along the stem; its upward movement from developing leaves reaches the young internodes (star) and induces stem elongation at the shoot apex. Throughout the flow along the stem, the signal results in bioactive GA signaling that controls cambial activity and fiber differentiation.

[See online article for color version of this figure.]