Flagellar strokes and flagellar waveforms of the normal and reverse beating mode. The flagellar activity of somatic cells before and after light stimulation. Light gray arrows indicate the direction of the effective flagellar strokes. (a) Time scale. (b) and (c) Dark-field images of somatic cells close to the anterior pole (see Figure 2d). Both images show the same cells (exposure time, 0.004 s). (b) The flagellar activity before the light was turned on (normal beating mode). (c) The flagellar activity immediately (1.0 s) after the light was turned on (light intensity: 20.8 μmol m-2 s-1). The flagella showed the reverse beating mode. (d) The frame indicates the analyzed area relative to the spheroid, and the black arrow indicates the spheroid's inherent moving direction. (e) and (f) Stylized representation of the recorded flagellar strokes of somatic cells before and immediately (1.0 s) after light stimulation. (g) and (h) Frames from high-speed captured microvideographs of the same somatic cell. The viewing angle is almost perpendicular to the bending plane of the flagella. (g) Normal beating mode (before light stimulation). (h) Reverse beating mode immediately (0.1 s) after light stimulation. (i) and (j) Superimposed flagellar waveforms derived from successive stop-motion, high-speed video frames of the cell shown in (g) and (h) that show complete stroke. Only one flagellum is shown. (i) Normal beating mode. (j) Reverse beating mode. (k) and (l) Superimposed flagellar waveforms of both flagella of a somatic cell in normal beating mode. To allow for the simultaneous tracing of both flagella, the viewing angle is almost parallel to the bending plane of the flagella. The interval between the flagellar traces in (k) and (l) is only 0.13 s.