Phototaxis in True Slime Mold Physarum polycephalum

Abstract

Phototaxis of plasmodium of true slime mold Physarum polycephalum was studied as a function of light wavelength and intensity. The change in the motive force of protoplasmic streaming (DPt) or isometric tension (DF/F0) was taken as the phototactic response. Three active spectral regions exist in the action spectrum of phototaxis. The blue light region (lmax = 490nm) or far-red light region (lmax = 720nm) induced negative taxis, and the red light region (lmax = 650nm) led to positive taxis. The absorption spectrum of plasmodial yellow pigments did not coincide with the maxima of the action spectrum. The time course of the phototactic response DPt was independent of intensity for a given wavelength so far as the intensity of stimulating light exceeded the threshold value, suggesting that light stimulation acted as a trigger for initiating the tactic movement. The mode of phototaxis resembled that of chemotaxis for motive force, i.e., the steady value of phototactic motive force DP changed from zero to 8-12 cm H2O in rather narrow intensity regions, and DP values were independent of the intensity of light so far as the intensity exceeded the threshold value L. When the slime mold was illuminated with blue (500nm, 510nm) and far-red (720nm) light, isometric tension increased with the intensity of light (I>L) while for red light (650nm) isometric tension did not show an appreciable change on illumination. © 1976, Japan Society for Cell Biology. All rights reserved.