Gravireaction of ciliates under variable accelerations

General information on the experiment

 1. Test Objectives

The swimming behaviour of unicellular organisms, the protists (ciliates) Paramecium and Stylonychia, has been investigated during the variable accelerations provided by the parabolic flights in order to determine the threshold for their gravity-dependent swimming behaviour (gravitaxis, gravikinesis).

 2. Brief description of the test and associated test equipment

It is well known that the membrane potential controls the swimming behaviour in ciliates. The physiological reaction of the cells to the acceleration vector can be directly derived from the analysis of video recordings. Samples of about 200 cells included are recorded in a dark field arrangement using video-camcorders. The records are evaluated postflight using a computer aided image analysis system on ground. Two modules allow to simultaneously record twelve individual cell samples of each species in every flight. The slow decrease of acceleration (1.8 g to µg and back to 1.8 g at a rate of 0.36 g/s) will allow to determine thresholds of graviresponses in large cell populations. Thresholds measured under increasing and decreasing acceleration conditions will be compared. The large number of parabola (90 in 3 flights) together with the large number of individual cells will guarantee a high statistical significance of the results.

For the experiment we will use two modules inserted and fixed within a rack, which is currently under construction. The modules have been specially developed for the recording of behaviour in ciliates and have been successfully used in more than hundred-forty flights in the drop tower of ZARM (University Bremen, Germany) and the drop shaft of JAMIC (Kamisunagawa, Japan); one of them even in the MICROBA VI flight (balloon experiment) in China.

The first module consists of six identical recording units, which are mounted on two platforms. Within one minute the whole inner cage can be softly reoriented by 90°. The free moving ciliates are included in Perspex-chambers (inner dimensions 3.5 mm x 3.5 mm x 1.6 mm) which are mounted on carrier plates for quick insertion. A dark field illumination is provided by a ring of 48 green LEDs. The swimming behaviour of the ciliates is recorded by commercial camcorders equipped with a macro-optic. For check of recording quality, a video multiplexer is provided. Time marks (for instance start of µg interval) can be recorded on videotape by means of coloured LEDs in the video field as well as using trigger signals on the sound tracks, or by using a conventional microphone. Control of all functions is realized by a switch box.

The second module is similar to the first one providing 6 additional recording units on three superlaying platforms.