title: Actin-dependent chloroplast anchoring is regulated by Ca(2+)-calmodulin in spinach mesophyll cells.
abstract: Chloroplasts are actively anchored at the appropriate intracellular regions to maintain advantageous distribution patterns under specific environmental conditions. Redistribution of chloroplasts is accompanied by their de-anchoring and re-anchoring, respectively, from and to the cortical cytoplasm. In spinach mesophyll cells, high-intensity blue light and Ca(2+) treatment induced the disappearance of the meshwork-like array of actin filaments surrounding chloroplasts, which was suppressed by a calmodulin antagonist. Regulatory mechanisms of chloroplast anchoring were investigated using plasma membrane (PM) ghosts, on which the cortical cytoplasm underlying the PM was exposed. Addition of an actin-depolymerizing reagent or > 1 µM Ca(2+) induced detachment of a substantial number of chloroplasts from the PM ghosts concomitant with disordered actin organization. Calmodulin antagonists and anti-calmodulin antibodies negated the effects of Ca(2+). In addition, Ca(2+)-induced detachment of chloroplasts was no longer evident on the calmodulin-depleted PM ghosts. We propose that chloroplasts are anchored onto the cortical cytoplasm through interaction with the actin cytoskeleton, and that Ca(2+)-calmodulin-sensitized de-anchoring of chloroplasts is a critical early step in chloroplast redistribution induced by environmental stimuli.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan. hideyasu@bio.sci.osaka-u.ac.jp
authors.forename: Hideyasu
authors.initials: H
authors.lastname: Takamatsu
authors.forename: Shingo
authors.initials: S
authors.lastname: Takagi
mesh_terms: D008841:Actin Cytoskeleton / Q000502:physiology; D000199:Actins / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D002736:Chloroplasts / Q000502:physiology*; D003593:Cytoplasm / Q000502:physiology; D008027:Light; D058503:Mesophyll Cells / Q000502:physiology*; D018724:Spinacia oleracea / Q000166:cytology* / Q000502:physiology
chemical_list: D000199:Actins; D002147:Calmodulin; D002118:Calcium