Behavior of cytoplasmic streaming in Nitella during centrifugation as revealed by the television centrifuge-microscope 1

Abstract

Using the prototype of newly developed centrifuge-microscope loaded with a video camera to produce an unflickering image, we observed the behavior of cytoplasmic streaming in the young internodal cell of Nitella axilliformis during centrifugation. At 1500 rpm (250×g) the majority of the flowing endoplasm collected at the centrifugal end of the cell, when the boundary between the accumulated endoplasm and the cell sap was “horizontal” and flat. By slowing down the speed of rotation to 1000 rpm (110×g), a clearly recognizable streaming was started, in the form of a thin layer moving against the centrifugal force on one side of the cell; and the endoplasm-cell sap boundary became tilted as if dragged by the stream overcoming the centrifugal force. When centrifugation was stopped, normal streaming soon resumed. The process was perfectly reversible. Prevention of streaming by cytochalasin B was shown to be due to the loss of motive force, and not to the increase in viscosity or gelation of the endoplasm. The streaming velocity-centrifugal force relation is not linear, which is explained by the thinning of the endoplasmic layer during centrifugation. Changes in streaming velocity induced by moderate centrifugal accelerations enabled us to estimate the motive force responsible for the streaming. It was calculated to be about 1 dyn·cm⁻², corresponding well with the data obtained by other methods.