Fig. 2. Correlation of wave propagation and cell movement in streamer NP377 slugs. (A) Brightfield image of a slug shown from below. To detect the optical density waves the average brightness was measured in small squares at the position of the cells. Four squares are shown (1-4); the cells are visible in the corresponding fluorescence image (B). The long rectangle over the midline of the whole slug indicates the position of the measuring window for the time-space plot (C). (B) Fluorescence image of the slug showing the GFP-labelled cells. The positions of the four cells at different time points of the sequence are indicated by white dots. (C) The time-space plot reveals the presence of several waves propagated from the tip to the back of the slug over a period of 46 minutes. The waves are visible as dark sloping bands; the white arrows point at three waves just before they seem to disappear in the rear part of the slug. To enhance the visibility of the waves, this time-space plot was created by using a sequence of subtracted images. (D) Graph showing the changes of velocity and average brightness of cell 1. The velocity is plotted in black, the intensity in grey. Owing to a drift in the brightfield signal, the intensity data were corrected by subtracting the values of a calculated linear regression line from the original data. The curves were smoothed by a running average over three data points. Broken lines mark the intensity peaks. (E) Periodic movement of cells 1, 5 and 6 from (B). (F) Cross-correlation analysis of the cell velocities. Scale bars: 100 µm.
