Localization of active MDR pumps within colonies. (A–D) Vertical transverse cross sections of BR-F colonies that were 36 h old, stained with ConA-AF (ConA) and NR. (A) A layer of NR-free cells covers the entire colony. (B and C) Details of the upper (B) and root (C) cells from the boxes in A are shown. (D) NR extrusion by the surface cell layer is reduced by removing the transcription factor Pdr1p and blocked by energy depletion (using NaN₃) or the absence of both Pdr5p and Snq2p MDR transporters. (E) A model of MDR gene regulation. (F) Pdr5p-GFP localization in the membrane of the upper cells and root tips compares well with that in the NR-free colony layer in A–C. (G) A model of Pdr5p and Snq2p distribution (violet) in colonies. (H) NR extrusion and transporter localization in colonies of different strains. wt, wild type.