Fig. 2. Localization of auxin and cell division activity in the maize root apex. Scale bar, 100 µm. (A-D) Control roots, intact, no treatments, stained for (A) histology (Orange G and Safranin), (B) BrdU and (C) auxin. Note that the auxin maximum (dark purple color) localizes in the columella initials/QC. (D) Control, as in C, but without incubation with the primary antibody. QC, quiescent center; PM, proximal meristem; RC, root cap. (E-P) Roots treated with NPA for (E-H) 24 hours; (I-L) 48 hours; (M-P) 24 hours NPA followed by no NPA for 24 hours and stained for auxin (E,I,M) and BrdU (F,G,J,K,N,O). G,K,O are enlargements of F,J,N respectively. H,L and P show the histology. rcj, root cap junction. (Q-V) Roots from which the root cap has been excised (Q,R) 24 hours, (S,T) 48 hours and (U,V) 72 hours earlier. Arrow in S points to heavily stained, auxin-rich region of the developing columella. (Q,S,U) auxin; (R,T,V) BrdU.