Possible association of actin filaments with chloroplasts of spinach mesophyll cells in vivo and in vitro |
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Authors: | T Kumatani N Sakurai-Ozato N Miyawaki E Yokota T Shimmen I Terashima S Takagi |
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Institution: | (1) Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka;(2) Department of Life Science, Graduate School of Life Science, University of Hyogo, Harima Science Park City, Hyogo |
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Abstract: | Summary. In palisade mesophyll cells of spinach (Spinacia oleracea L.) kept under low-intensity white light, chloroplasts were apparently immobile and seemed to be surrounded by fine bundles
of actin filaments. High-intensity blue light induced actin-dependent chloroplast movement concomitant with the appearance
of a couple of long, straight bundles of actin filaments in each cell, whereas high-intensity red light was essentially ineffective
in inducing these responses. The actin organization observed under low-intensity white light has been postulated to function
in anchoring chloroplasts at proper intracellular positions through direct interaction with the chloroplasts. Intact chloroplasts,
which retained their outer envelopes, were isolated after homogenization of leaves and Percoll centrifugation. No endogenous
actin was detected by immunoblotting in the final intact-chloroplast fraction prepared from the leaves kept under low-intensity
white light or in darkness. In cosedimentation assays with exogenously added skeletal muscle filamentous actin, however, actin
was detected in the intact-chloroplast fraction precipitated after low-speed centrifugation. The association of actin with
chloroplasts was apparently dependent on incubation time and chloroplast density. After partial disruption of the outer envelope
of isolated chloroplasts by treatment with trypsin, actin was no longer coprecipitated. The results suggest that chloroplasts
in spinach leaves can directly interact with actin, and that this interaction may be involved in the regulation of intracellular
positioning of chloroplasts.
Correspondence and reprints: Department of Biology, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka,
Osaka 560-0043, Japan.
Present address: Tsukuba Research and Development Center, Fuji Oil Co., Ltd., Tsukuba-gun, Ibaraki, Japan. |
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Keywords: | : Actin cytoskeleton Chloroplast positioning Chloroplast outer envelope Filamentous actin Spinacia oleracea Mesophyll cell |
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