Plant and Cell Physiology Advance Access originally published online on November 19, 2008
Plant and Cell Physiology 2009 50(1):129-140; doi:10.1093/pcp/pcn177
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Differential Positioning of C4 Mesophyll and Bundle Sheath Chloroplasts: Recovery of Chloroplast Positioning Requires the Actomyosin System
1Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi, 464-8601 Japan
2Research Institute of Life and Health Sciences, Chubu University, Kasugai, Aichi, 487-8501 Japan
*Corresponding author: E-mail, taniguti{at}agr.nagoya-u.ac.jp; Fax, +81-52-789-4063.
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Abstract |
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In C4 plants, bundle sheath (BS) chloroplasts are arranged in the centripetal position or in the centrifugal position, although mesophyll (M) chloroplasts are evenly distributed along cell membranes. To examine the molecular mechanism for the intracellular disposition of these chloroplasts, we observed the distribution of actin filaments in BS and M cells of the C4 plants finger millet (Eleusine coracana) and maize (Zea mays) using immunofluorescence. Fine actin filaments encircled chloroplasts in both cell types, and an actin network was observed adjacent to plasma membranes. The intracellular disposition of both chloroplasts in finger millet was disrupted by centrifugal force but recovered within 2 h in the dark. Actin filaments remained associated with chloroplasts during recovery. We also examined the effects of inhibitors on the rearrangement of chloroplasts. Inhibitors of actin polymerization, myosin-based activities and cytosolic protein synthesis blocked migration of chloroplasts. In contrast, a microtubule-depolymerizing drug had no effect. These results show that C4 plants possess a mechanism for keeping chloroplasts in the home position which is dependent on the actomyosin system and cytosolic protein synthesis but not tubulin or light.
Keywords: Actin filament - C4 photosynthesis - Chloroplast - Eleusine coracana - Zea mays
Abbreviations: BDM, 2,3-butanedione monoxime; BS, bundle sheath; BSA, bovine serum albumin; DMSO, dimethylsulf-oxide; FITC, fluorescein isothiocyanate; M, mesophyll; ML-7, 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine; PBS, phosphate-buffered saline.
3Present address: Marukome Co. Inc., Amori 883, Nagano, 380-0943 Japan.
(Received October 13, 2008; Accepted November 16, 2008)
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