Abstract
To clarify involvement of auxin efflux carrier PIN in the phototropism, we have investigated the hypocotyl phototropism of Arabidopsis pin mutants. Since PIN3 is thought to be involved in lateral translocation of auxin and PIN7 is most closely related to PIN3, pin3 and pin7 single mutants and pin3 pin7 double mutants were analyzed. A typical bell-shaped fluence-response curve for the pulse-induced positive phototropism (PIPP) was identified in the wild type. Although PIPP was also observed in the pin3, pin7, and pin3 pin7 mutants, maximal responses were reduced by 50%, 20%, and 70%, respectively. Time-dependent phototropism (TDP) was induced in the wild-type when the duration of phototropic stimulation of blue light exceeded 3 min. TDP also appeared in the pin3, pin7, and pin3 pin7 mutants, but phototropic curvatures were reduced in the mutants. The results indicate that PIN3 and PIN7 are involved in both PIPP and TDP. Interestingly, the hypocotyl phototropism induced by continuous irradiation of blue light was not impaired even in the pin3 pin7 double mutants. The result suggests that factors other than PIN3 and PIN7 contribute to the asymmetrical distribution of auxin.
