Fig. 8. Model for interaction of PGPs and PINs in the local auxin distribution in meristematic tissues. (A) Enhanced effects (20%) of estradiol-induced PIN1 overexpression on root length and hypocotyl twisting in the pgp1pgp19 mutant when compared with wild type, confirming the antagonistic roles of PIN1 and PGP1/PGP19 in seedling development. Error bars represent s.e.m., n=20. (B) Immunolocalization of PIN2 and PGP19-HA. Polar and non-polar localization of PIN2 and PGP19-HA in the root epidermis, respectively. Expression of PGP19 is higher in the endodermis and the pericycle that form the border between acropetal and basipetal auxin streams. (C) Model of PIN and PGP interaction. PGPs and PINs interact intermoleculary at the PIN-containing polar domain, possibly regulating the PIN stability in the plasma membrane. The PGPs remaining in these cells control the cellular auxin pool available for the PIN transport. In pgp1pgp19, the cellular auxin concentration is increased and, therefore, the PIN transport is enhanced but less focused.