Fig. 5. The oscillatory nature of cell motility. Representative traces of growth rate against time for the cell area gained (red) and lost (blue) (A,B), and the centroid velocity against time (C,D) of vegetative wild-type (A,C) and myosin-II-null (B,D) cells expressing GFP. All cells were imaged in SB. (E) Cross-correlogram between the rates of gain-of-area and loss-of-area are shown for vegetative cells. Cross-correlation (Chatfield, 2003) was calculated with home-developed Perl scripts as the average for each cell population. For a cell sample i, it was defined as:

where (V) indicates the standard deviation of V and T_i is the recording period of the sample i. Area around lag 0 in E is shown at higher magnification in F. Wild-type (WT; red and green) and myosin-II-null (myosin II-; blue and orange) cells in buffer without (SB; red and blue) and with (HI; green and orange) 100 mM sorbitol. The averages of correlation functions from 59 (red), 59 (green), 50 (blue) and 49 (orange) cells are shown. The lines of apparently varying width actually consist of vertical lines representing mean ± s.e.m.