Discontinuous Change in Membrane Activities of Plasmodium of Physarum polycephalum Caused by Temperature Variation: Effects on Chemoreception and Ameboid Motility

Abstract

Variations in the surrounding temperature altered membrane activities at the critical temperature, Tc = 15.degree. C in plasmodium of the true slime mold P. polycephlum. Changes in the membrane and zeta potentials, which were induced by chemical stimuli, decreased when the temperature decreased below Tc. The adsorption energy of a -CH2- group on the membrane changed discretely by about 100 cal/mol at Tc. Decreasin the temperature sharply diminished the extension of psuedopodia by a factor o 1/10 at Tc, while the motive force of protoplasmic streaming remained constant. This suggests that the formation of pseudopodia and the generation of motive force are different functions in ameboid motility. Results indicate that the surface membrane of the plasmodium undergoes a conformational change at Tc. The mechanisms of chemoreception and motility in plasmodium are discussed.