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Figure 3.72 Formation and trafficking of PIPs within a plant cell. PIPs belonging to the PIP2 group (in yellow) form homo- or heterooligomers by associating with PIP1 isoforms (in green). PIP oligomers transit through the Golgi apparatus and trans-Golgi network (TGN) and are then loaded into secretory vesicles and routed to the plasma membrane. In the circle is shown the topological structure of the aquaporin monomer AQP1 (Murata et al. 2000), with six membrane-spanning α-helices (1-6) connected by five loops (A-E). The loops B and E form two short hydrophobic α-helices (in red) dipping halfway into the membranes, which, together with the membrane-spanning helices, create a pore with high specificity. From Chaumont and Tyerman (2014). Reproduced from F. Chaumant and S.D. Tyerman, Plant Phys 164: 1600-1618, Copyright American Society of Plant Biologists.