The PIN proteins are named for the pin-formed mutant

PIN1 is expressed in the vascular tissue. Asymmetric distribution on the plasma membrane allows directional transport of auxin. The distribution of PIN proteins determines the direction of auxin fluxes in different tissues. Auxin redistribution triggers developmental responses: Leaf formation, Gravitropism, Establishment of the apical-basal axis during embryonic development. PIN1 cycle between the plasma membrane and endosome not in gnom mutant. PIN1 is required to transport auxin to the periphery of the apical meristem and to induce leaf formation. Polarised distribution of the PIN1 protein directs auxin to the organ primordial.