The Journal of Cell Biology, Vol 93, 735-742, Copyright © 1982 by The Rockefeller University Press
Effects of exogenous proteins on cytoplasmic streaming in perfused Chara cells
EA Nothnagel, JW Sanger and WW Webb
Cytoplasmic streaming in characean algae is thought to be generated by
interaction between subcortical actin bundles and endoplasmic myosin. Most
of the existing evidence supporting this hypothesis is of a structural
rather than functional nature. To obtain evidence bearing on the possible
function of actin and myosin in streaming, we used perfusion techniques to
introduce a number of contractile and related proteins into the cytoplasm
of streaming Chara cells. Exogenous actin added at concentrations as low as
0.1 mg/ml is a potent inhibitor of streaming. Deoxyribonuclease I (DNase
I), an inhibitor of amoeboid movement and fast axonal transport, does not
inhibit streaming in Chara. Fluorescein-DNase I stains stress cables and
microfilaments in mammalian cells but does not bind to Chara actin bundles,
thus suggesting that the lack of effect on streaming is due to a surprising
lack of DNase I affinity for Chara actin bundles. Heavy meromyosin (HMM)
does not inhibit streaming, but fluorescein-HMM (FL-HMM), having a
partially disabled EDTA ATPase, does. Quantitative fluorescence micrography
provides evidence that inhibition of streaming by FL-HMM may be due to a
tendency for FL-HMM to remain bound to Chara actin bundles even in the
presence of MgATP. Perfusion with various control proteins, including
tubulin, ovalbumin, bovine serum albumin, and irrelevant antibodies, does
not inhibit streaming. These results support the hypothesis that actin and
myosin function to generate cytoplasmic streaming in Chara.
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