Geotaxis of the Acellular Slime Mold Physarum polycephalum.

Kurzfassung

Gravity is able to influence not only the contraction frequency of the slime mold but also the direction of its locomotion (geotaxis). This behavior allows the organism to find and stay in favorable environmental conditions. Despite many efforts the perception mechanism for the gravistimulus remains unknown. Experiments involving real and simulated weightlessness as well as horizontal turn experiments have shown that the modulation of the contraction frequency is followed by regulation phenomena. The same type of response is performed upon stimulation of the migrating slime mold with light. Experiments indicate that the mitochondria play an important role in changing the contraction rhythm in response to external stimuli. The simultaneous induction of the light and O-g reactions on the fast rotating clinostat lead to a superposition of the two opposite reactions. This mutual influence of the light and gravity reactions on one another are discussed with regard to the role the chondriome plays not only in the regulation of the contraction frequency but also in the perception of the respective stimulus.