The exocyst’s role in root growth. The exocyst is required for root growth in two developmental contexts to affect (A) cell production; and (B) cell length. Table above graphs shows how parameters determining primary root growth are affected by exocyst mutations; values shown are percentages of the Col-0 value for each parameter. Bars in graphs A and B represent (from white to black): Col0 (wild-type), exo70A1, sec5a exo70A1, sec8-4 exo70A1, sec8-3 and exo84b-1. In the meristem exocyst mutations reduce the cell production rate (A), but not the length of cells in the cortical cell file (B). However, in the transition and elongation zones, where new cells are rarely produced in either wild-type or exocyst mutant roots, mutation of the exocyst leads to severely reduced cortical cell elongation (B).