Physicochemical Basis of Information Processing in Ameboid Cells in Relation to Perception of Lower Organisms

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1) Halobacterium halobium shows positive and negative phototaxis. Receptors of the phototaxis were identified. The photochemistry of receptor pigments was investigated with flash-photolysis and low-temperature spectrophotometry.2) Uni-cellular organisms are able to perceive changes of their environment behave accordingly just as higher animals do. A mechanism of information processing in true slime mold, Physarum polycephalum is investigated. This organism extends like a sheet at the frontal part, and intricate veins develop toward the rear, in which the protoplasmic sol moves to and fro very regularly.The period of this regular movement is about 2 minutes. Because this regular movement accompanies changes of the thickness of the vein, oscillatory signals of transmitted light can be observed. We have analyzed the dynamic behavior of the intrinsic rhythm with the help of computer image processing. When a part of the plasmodium is stimulated with temperature, chemicals or light, waves of thickness oscillation propagate throughout the organism, the phase around the stimulated region being advanced or retarded for attractants or repellents, respectively. This suggests that the intracellular information processing within the plasmodium is related to dynamic cooperative behavior in a population of coupled non-linear oscillators.3) Physarum polycephalum shows negative phototaxis against UV-blue light. Action spectrum was determined, which accords well with action spectrum for generation of super oxide anion. In the absence of oxygen, no negative taxis is observed. These facts imply that super oxide anion is a mediator for the negative taxis.