Abstract
We have created a new computerized video method [the Tracker-Cell Movement Analyzer (TCMA)] for flexible and detailed time-related tracking and analyses of cell movements, especially behavioral responses to light stimuli. TCMA displays the swimming tracks of the individual cells in consecutive time segments of variable length using different colors to represent different time segments; it automatically performs statistical analyses of the swimming directions and velocities of the cells in each time segment. As an example of its many possible applications, an analysis of the circadian rhythms of phototactic orientation and motility in Chlamydomonas was performed. It is thus clearly demonstrated that the velocity of motile cells, the phototactic orientation and the percentage of motile cells, changed rhythmically in a circadian manner, all in the same phase, i.e. the maximum occurred at the “subjective dawn” and the minimum at the “subjective dusk”. These facts can quantitatively account for the observed circadian change in the photoaccumulation activity.
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