An Optical Model for Phototactic Orientation in Dictyostelium discoideum Slugs |
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Authors: | Poff, Kenneth L. Fontana, Donna R. Hader, Donat-P. Schneider, Michael J. |
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Affiliation: | 1Department of Energy, Plant Research Laboratory, Michigan State University East Lansing, Michigan 48824, U.S.A. 2Fachbereich Biologie-Botanik der Universität Marburg Lahnberge, D-3550 Marburg, Federal Republic of West Germany 3Department of Natural Science, The University of Michigan-Dearborn Dearborn, Michigan 48128, U.S.A. |
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Abstract: | The optical properties of an enlarged optical model of the tipof a slug (a glass tube filled with sucrose solution) of Dictyosteliumdiscoideum were studied to validate the hypothesis that theorganism orients itself with respect to lateral light usinga lens effect: Light is focussed by refraction onto the distalside of the slug where the higher "signal" compared to the frontside causes a turn toward the light. Light was effectively focusedeven when the model deviated only as little as 10° fromthe light direction. Slugs of D. discoideum strains HO596 and HO813 show bidirectionalphototaxis: They orient themselves at some angle on either sideof the incident light beam. This angle is {small tilde}80°in HO596 and {small tilde}70° in HO813. We suggest thatthis phenomenon can be explained by the optical properties ofthe slug such as absorption and scattering, shape of the tipor location and extension of the light-sensitive zone. The angleof orientation with respect to light is regulated by a balancebetween a turn toward and a turn away from the light direction. (Received October 15, 1985; Accepted February 10, 1986) |
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