Polar PIN Localization Directs Auxin Flow in Plants.

The article reports that the phytohormone auxin plays a major role in plant growth. To determine the direction of auxin flow researchers studied the directional auxin translocation during root gravitropism in Arabidopsis thaliana. They designed hemagglutinin epitope-tagged PIN1 and PIN2 genes under the transcriptional control of the PIN2 promoter. It was observed that in cortex cells, both proteins were localized at the lower basal side. Researchers tested the relationship between polarity and the direction of auxin flow by examining auxin translocation during gravity response. It was found that the localization of PIN proteins at the upper side of epidermal cells was related to their ability to facilitate upward auxin movement for root gravitropic response. Finally it was concluded that PIN polarity is a primary direction determining factor in auxin transport in meristematic tissues. It also provides information on how auxin flows can be redirected through rapid changes in PIN polarity in response to developmental and environmental signals.