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Actin-based photo-orientation movement of chloroplasts in plant cells

Shingo Takagi

Department of Biology, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan

View larger version (25K): [in a new window]   Fig. 1. Schematic demonstration of photo-orientation movement of chloroplasts in various types of plant cells. Typical intracellular distributions of chloroplasts observed under dim or strong light in the coenocytic alga Vaucheria, the green alga Mougeotia and the angiosperm Lemna are shown. N, nucleus. Modified from Senn (1908).

View larger version (74K): [in a new window]   Fig. 2. Accumulation of chloroplasts in the cell apex of the coenocytic green alga Dichotomosiphon. (A-D) Dim blue light induced the accumulation of chloroplasts in the apical region of a cylindrical cell of Dichotomosiphon over a period of 0-90 min. (E) Microtubules (MT; green) and (F) actin filaments (AF; red) in the apical region filled with chloroplasts (blue) were visualized using fluorescence-labelled probes. Scale bar: 20 µm.

View larger version (68K): [in a new window]   Fig. 3. Photo-orientation movement of chloroplasts in the aquatic angiosperm Vallisneria gigantea epidermal cells. Cross-sections of leaf epidermal cells, in which chloroplasts accumulated along the outer periclinal wall (OPW) under dim light (A) or along the anticlinal walls (AW) under strong light (B). V, central vacuole. Scale bar: 5 µm.

View larger version (136K): [in a new window]   Fig. 4. Accumulation of mitochondria with chloroplasts in Vallisneria epidermal cells. Paradermal sections of Vallisneria epidermal cells under dim light, in which mitochondria (Mit) accumulated along the outer periclinal wall together with chloroplasts (Chl).

View larger version (18K): [in a new window]   Fig. 5. Light-dependent changes in motility of chloroplasts in Vallisneria epidermal cells. The motility of individual chloroplasts was determined after digitization of images obtained by video microscopy of Vallisneria epidermal cells under dim red light in the presence (filled symbols) or absence (open symbols) of dichlorophenyl dimethylurea (DCMU), an inhibitor of photosynthetic electron transport. Modified from Dong et al. (1996).

View larger version (176K): [in a new window]   Fig. 6. Different configurations of actin filaments in Vallisneria epidermal cells. Actin filaments along the outer periclinal walls were visualized by fluorescence-labelled phalloidin in Vallisneria epidermal cells under dim red light (A), strong blue light (B) or microbeam irradiation with strong blue light (C).

View larger version (163K): [in a new window]   Fig. 7. Avoidance response of chloroplasts induced in partially irradiated Spinacia oleracea mesophyll cells over time: (A) 28 min, (B) 45 min, (C) 119 min and (D) 128 min. Partial irradiation of Spinacia mesophyll cells with strong blue light induced the localized avoidance response of chloroplasts, together with the formation of cytoplasmic strands (each pair of arrows) that moved freely in the irradiated cells. The lower half of the cells was irradiated. Scale bar: 10 µm.

View larger version (82K): [in a new window]   Fig. 8. Actin filaments associated with chloroplasts squeezed from spinach mesophyll cells. Chloroplasts squeezed out from manually dissected spinach mesophyll cells (A) were stained with fluorescence-labelled phalloidin (B), and the images were superimposed (C). Scale bar: 5 µm.

View larger version (45K): [in a new window]   Fig. 9. Immunoblot analysis of actin associated with isolated chloroplasts from Spinacia oleracea. The association of actin with the isolated intact chloroplasts from spinach leaves was examined by immunoblotting of the chloroplasts immediately after isolation (lane 1), and incubation for 0 min (lane 2) and 30 min (lane 3) with exogenously added chicken skeletal muscle F-actin. The arrow indicates the position of the actin band. Molecular markers are indicated on the left.

View larger version (105K): [in a new window]   Fig. 10. Intracellular arrangement of chloroplasts in terrestrial plant leaves. Intracellular arrangement of chloroplasts is demonstrated in a cross-section of the adaxial part of a Spinacia oleracea leaf (A) and in a paradermal section of the parenchyma cells of Maesa japonica (B). Arrowhead in A indicates the stoma, while the yellow circles in B indicate intercellular spaces. Scale bars: 25 µm.