Step-up photophobic response in the ciliate,Stentor coeruleus |
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Authors: | Pill-Soon Song Donat-P Häder Kenneth L Poff |
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Institution: | (1) Department of Chemistry, Texas Tech. University, 79409 Lubbock, TX, USA;(2) Fachbereich Biologie-Botanik, Philipps-Universität Marburg, Lahnberge, D-3550 Marburg, Germany |
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Abstract: | The avoidance by Stentor coeruleus of a light trap is caused by a step-up photophobic response. The phobic response invariably consists of a delay of about 200 ms, a stop response, a turn to one side, and resumption of swimming in the new direction. After this the cells enter a refractory period of 1–3 s following a phobic response, during which they will not give a second response. Phobic responses can be elicited by spatial and temporal increases in light intensity. The action spectrum for the step-up photophobic response resembles the absorption spectrum of stentorin, the proposed photoreceptor pigment, and of its chromophore, hypericin.The phobic response is specifically inhibited by the protonophorous uncouplers TPMP+ and FCCP but not by the ionophores gramicidin and A23187. Since the uncouplers block light-induced membrane potential changes at the same concentrations, it has been proposed that the primary photoreception causes a light-induced potential change, which in turn, induces a motor response.Abbreviations TPMP+
triphenyl methyl phosphonium bromide
- FCCP
carbonylcyanide p-trifluoromethoxy-phenylhydrazone |
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Keywords: | Hypericin Ionophores Light-induced membrane potential Photophobic response Stentor Uncouplers |
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