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| Home > Publications database > Untersuchungen zur photosensorischen Transduktion bei $\textit{Euglena gracilis}$, insbesondere zur Rolle von Calcium |
| Home > Publications database > Untersuchungen zur photosensorischen Transduktion bei $\textit{Euglena gracilis}$, insbesondere zur Rolle von Calcium |
| Book/Report | FZJ-2018-03192 |
1989
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18697
Report No.: Juel-2323
Abstract: I. To test the shading hypothesis for phototaxis of Euglena gracilis, I performed behaviour experiments in which shading of the paraflagellar body by the stigma was simulated by means of dark pulses. a) Dark pulses shorter than latency time did not induce a tumbling response. The measured latency time (500 ms) corresponds very well with the calculated shading time of the paraflagellar body by the stigma, which was derived from the morphological conditions of the cell. Experiments with periodical dark pulses showed that not only the shading (dark pulse) but also the following light that stops the tumbling answer is a sensoric signal for the cell. The illumination which follows a shading during one turning of the cell, makes the start of a new tumbling answer as a consequence of further shading possible. If we accept the shading hypothesis, we have to require such a fast turning-off mechanism for Euglena grad/is. b) The experiments with periodic dark pulses during phototactic orientation show that consecutive dark and light pulses induce the positive phototaxis as well. However, if the dark pulse is longer than 300 ms, the phototaxis will be considerably reduced. This time corresponds to the latency time, which is necessary for causing the tumbling answer. This correspondence is another support for the shading hypothesis, which explains the phototaxis of Euglena gracilis by means of short successive tumbling answers. II. a) According to the model of the photosensoric transduction, a stimulus-dependent Ca$^{2+}$ influx is necessary to induce thea tumbling answer. I could show in behaviour experiments that, though the tumbling answer is modified in dependence of the extracellular Ca$^{2+}$ concentration, it is not suppressed by an extremely low Ca$^{2+}$ concentration of 10$^{-9}$ mol/l. These results are not in accordance with the model of Doughty and Diehn. Therefore I investigated if and how the tumbling answer: and the phototaxis are influenced by cyclic nucleotides. b) cGMP shortens the time of the tumbling answer, whereas it changes neither the latency time nor the reversal time for positive and negative phototaxis. The experiments [...]
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