Effects of localized photic stimulation on amoeboid movement and their theoretical implications.
The uroids, the posterior, middle and anterior segments of the intermediate body regions, and the frontal zones of Amoeba proteus were exposed, separately or in different combinations, to local increases or decreases of light intensity. In general, an increase of luminosity promotes contraction, and its decrease induces relaxation in any body region of amoeba. The contracting or relaxing effects of luminosity changes are detectable along the whole length of the cortical tube, including its most anterior part. The response induced by stimulation of the tip of an advancing pseudopodium is functionally opposed to the reaction elicited by the same stimulus acting on all other body regions. The uroidal retraction and frontal extension are accelerated by illumination any segment of the cortical tube, or by shading the frontal zone. They slow down when shade is applied to any part of the tube, or light to the front alone. The motor efficiency of the light-induced contraction is modified by the position of the simulated area in respect to the adhesion sites. Velocities of uroidal retraction and frontal extension depend (in the same degree as on the cortical contraction) on the availability of frontal openings accessible for the endoplasmic outflow from the cortical tube. Thus, the uroid accelerates when more fronts are formed, and an older advancing pseudopodium slows down when it has to compete with new fronts. It is concluded in general that the movement of amoeba depends on the contractile activity of the whole cell cortex which plays the motor role, and on the opening or obscuring the frontal breaches in the cortical envelope which perform the controlling and steering roles in locomotion.
D000656:Amoeba / Q000502:physiology*; D000818:Animals; D004721:Endoplasmic Reticulum / Q000502:physiology; D009068:Movement; D010775:Photic Stimulation