#pin1

Despite the abundant evidence correlating PIN1 distribution in the leaf with auxin canalization and vein formation, pin1 mutants have surprisingly mild phenotypes (Figure 19.23). For example, the pin1/pin6 double mutant leaf shown in Figure 19.23B has an altered shape and a defective venation pattern, but the basic hierarchical structure of the veins is still intact, indicating that other factors also contribute to auxin canalization.

PIN1 in the epidermal layer of the developing leaf directs auxin to convergence points along the leaf margin (Figure 19.22A). (...) Again, tertiary vein formation is guided by the canalization mediated by PIN1 proteins (Figure 19.22B).

Based on the orientations of the PIN1 proteins, auxin is directed to a convergence point in the L1 layer of the leaf primordium initial (P0).