Photon Correlation Analysis of Protoplasmic Streaming in the Slime Mold Physarum Polycephalum

Abstract

Protoplasmic streaming is one of the most rapid and spectacular forms of intracellular motion. If a small area of the plasmodium of the slime mold Physarum polycephalum is examined under a microscope of moderate power one can see an intricate latticework of large and small veins in which particles flow at speeds up to about 1 mm sec⁻¹ in one direction, slow to a stop, build up to a similar speed in the opposite direction, again slow to a stop, and then resume streaming in the original direction. This entire cycle of alternating or “shuttle” streaming repeats approximately every 90 sec at ordinary room temperatures. Protoplasmic movement can also be detected in all eukaryotic cells at some stage of development, in the generation of movement in certain protozoa, white blood cells, and fibroblasts (see the articles in Ref. 1 and 2). Unidirectional streaming persists throughout the life of many algal cells such as Nitella and Chara.³ Over two hundred years have passed since Corti first observed protoplasmic streaming in 1774, and yet we still do not understand the origin of the force that drives the streaming motion. We show here that laser photon correlation spectroscopy provides a rapid, objective method to study properties of the flowing endoplasm and can reveal underlying structural changes which are intimately associated with the streaming mechanism.