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Methods for Measuring Phototaxis of Cell Populations and Individual Cells
Author(s) -
Feinleib Mary Ella Harman,
Curry George M.
Publication year - 1967
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1967.tb08396.x
Subject(s) - phototaxis , stimulus (psychology) , optics , population , photoresistor , wavelength , optical path length , light beam , biophysics , physics , biology , botany , medicine , psychology , environmental health , psychotherapist
Two quantitative methods have been devised for studying the phototactic response of Chlamydomonas . In the first procedure, the movement of a cell population is continuously monitored photometrically, yielding a permanent record of the time course of the response. The monitoring system consists of a pair of photovoltaic cells connected in a comparison circuit, and a dim red light which passes through the swimming chamber and strikes the photocells. A stimulus beam enters the chamber at right angles to the monitoring light. The movement of algae towards the stimulus light produces a difference in output between the photocells. With a continuous stimulus, this difference increases in a nearly linear fashion for several ninutes. The slope of the linear portion depends on such factors as stimulus ntensity and wavelength and is used as the index of the response. In the second procedure, a photomicrographic method is used to resolve the population response into its components; i.e ., the number of cells responding, the directness of the swimming path, and the rate of swimming. The photographs are taken with a fixed exposure time, during which each cell in the field describes a swimming track on the film. Swimming rate is determined by measuring the length of the photographed track, while directness of path is indicated by the angle between the track and the stimulus light beam. The number of cells going towards the light is calculated from counts made while observing the culture through the microscope. These methods have been used to investigate the dependence of phototaxis on stimulus intensity and wavelength, age of culture, and pre‐illumination. This work formed a portion of a doctoral thesis submitted by one of the authors (M. E. Feinleib) to Harvard University, Cambridge, Mass. The work was supported in part by a U.S. Public Health Fellowship, No. FI‐GM‐17, 305–04, and by a National Science Foundation research grant, No. G14266.