Fig. 6. Changes in distribution of traction stress generated by a mhcA^– Dictyostelium cell during a `slow recoil' retraction. (A-J) A time series of traction vector maps obtained from a mhcA^– cell moving in the general direction indicated (arrow), during one cycle of movement. An asymmetrical distribution of traction stress occurs slowly (A-E), but more rapidly than in mlcE^– cells. Regions of highest 90th percentile traction stress (purple, red) enlarge at the rear and extend along the lateral cell edges. During retraction (R in E) at the rear (arrow) traction stresses gradually decrease, particularly at the rear (E-J), while at the same time protrusion (P in E) is occurring at the front where low tractions are present (E-J). Bar, 3 µm. (K) Plots of the 90th percentile traction stress (red), instantaneous speed (green), cell area (blue), shape factor (yellow) corresponding to panels A-J. The slow recoil retraction (R) occurs between 15 to 27 seconds, as indicated by the vertical dotted lines. Note that for illustrative purposes the color scale represents a range of magnitudes that is 25 times less than the one used for the wild-type cells in Figs 3 and 4.