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Actomyosin‐based motility of endoplasmic reticulum and chloroplasts in Vallisneria mesophyll cells *
Author(s) -
Liebe Susanne,
Menzel Diedrik
Publication year - 1995
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1016/0248-4900(96)85282-8
Subject(s) - endoplasmic reticulum , biology , chloroplast , myosin , microbiology and biotechnology , cytoplasmic streaming , actin , thapsigargin , cytokinesis , intracellular , biophysics , cell , biochemistry , cell division , gene
Summary— Intracellular localization and motile behaviour of the endoplasmic reticulum (ER), plastids and mitochondria were studied in living mesophyll cells of Vallisneria using the vital fluorochrome 3,3'‐dihexyloxacarbocyanine iodide (DIOC 6 (3)). In quiescent cells, the ER was composed of a three‐dimensional network of tubular and lamellar elements. Chloroplasts were distributed evenly throughout the cell periphery and appeared embedded within the ER network. The ER network was relatively stationary, with the exception of rare motile episodes occurring as movement of tubular ER strands and adjacent areas of the polygonal network in localized areas of the cell. During experimental induction of streaming, most of the lamellar ER elements transformed into tubules and together with the chloroplasts they began to translocate to the anticlinal walls to establish the circular streaming around the circumference of the cell. Microwave‐accelerated fixation followed by immunofluorescence revealed an hitherto unknown phase of actin reorganization occurring within the cells and most interestingly at the surface of the chloroplasts during streaming induction. Myosin was localized in an ER‐like pattern in quiescent as well as in streaming cells, with bright fluorescent label localized on mitochondria and proplastids. In addition, myosin label appeared on the surface of the chloroplasts, preferentially in streaming mesophyll cells. Motile activities were impeded by the actin‐depolymerizing drug cytochalasin D (CD), the thioreagent N‐ethylmaleimide (NEM), and thapsigargin, an inhibitor of the ER‐Ca 2+ ‐ATPase. These inhibitors also interfered with the integrity of actin filaments, the intracellular distribution of myosin and calcium‐homeostasis, respectively. These effects suggested an obligate association of at least one type of myosin with the membranes of ER and smaller organelles and are consistent with the appearance of another type of myosin on the chloroplast surface upon streaming induction.