Slower primary root growth in exocyst mutants is associated with shorter root growth zones. (A) Root growth on vertical plates is slower in exocyst mutants than Col-0, with defects ranging from mild (e.g. exo70A1-2) to quite severe (e.g. exo84b-1) (n = 8–19 roots for each genotype; error bars represent standard error). (B) The number of cells in the meristem, transition, and elongation growth zones is reduced in exocyst mutants in correlation with the root growth defect. Brassinosteroid (bri1 (SALK_003371), det2-1) and auxin transport (pin2-1, aux1-7) mutants, as well as brefeldin A (BFA)-treated roots are shown for comparison. Error bars for meristem and elongation zone data shown in Figure 2. (C-L) The shorter growth zones in exocyst mutants include shorter meristems that maintain a structure similar to wild-type. (C-F) Confocal images of 8 day old seedling root tips stained with propidium iodide; white triangles and yellow triangles mark the distal and proximal ends of the meristem (i.e. the MZ) (bar = 100 microns applies to C-F). (G-J) Confocal images of 8 day old propidium iodide-stained mutant roots (H-J) show expression of pWOX5-GFP restricted to the quiescent center and similar to wild-type (G) (bar = 50 microns). (K-L) Confocal images of root tips expressing PLT1-YFP driven by its native promoter in sec8-3 (L) and a wild-type sibling (K) (bar = 50 microns).