title: Blue-light-induced rapid chloroplast de-anchoring in Vallisneria epidermal cells.
abstract: In the outer periclinal cytoplasm of leaf epidermal cells of an aquatic angiosperm Vallisneria, blue light induces "chloroplast de-anchoring", a rapid decline in the resistance of chloroplasts against centrifugal force. Chloroplast de-anchoring is known induced within 1 min of irradiation with high-fluence-rate blue light specifically, preceding the commencement of chloroplasts migration toward the anticlinal cytoplasm. However, its regulatory mechanism has remained elusive, although pharmacological analysis suggested that a calcium release from intracellular calcium stores is necessary for the response. In search of the responsible photoreceptors, immunoblotting analysis using antibodies against phototropins demonstrated that cross-reactive polypeptides of 120-kDa exist in the plasma-membrane fraction prepared from the leaves. In vitro phosphorylation analysis revealed that 120-kDa polypeptides were phosphorylated by exposure to blue light in a fluence-dependent manner. The blue-light-induced phosphorylation activity was sensitive to a Ser/Thr kinase inhibitor, staurosporine, and unusually was retained at a high level for a long time in darkness. Furthermore, phototropin gene homologs (Vallisneria PHOTOTROPIN1 and PHOTOTROPIN2) expressed in leaves were isolated. We propose that calcium-regulated chloroplast de-anchoring, possibly mediated by phototropins, is an initial process of the blue-light-induced avoidance response of chloroplasts in Vallisneria.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka, 560-0043, Japan.
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Sakai
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Inoue
authors.forename: Akiko
authors.initials: A
authors.lastname: Harada
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Shimazaki
authors.forename: Shingo
authors.initials: S
authors.lastname: Takagi
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism / Q000528:radiation effects; D002736:Chloroplasts / Q000378:metabolism* / Q000528:radiation effects*; D003429:Cross Reactions; D017343:Genes, Plant; D031321:Hydrocharitaceae / Q000166:cytology* / Q000235:genetics / Q000528:radiation effects*; D042541:Intracellular Space / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation / Q000528:radiation effects; D056949:Phototropins / Q000737:chemistry / Q000378:metabolism; D059828:Plant Cells / Q000378:metabolism* / Q000528:radiation effects; D019441:Plant Epidermis / Q000166:cytology* / Q000528:radiation effects; D016415:Sequence Alignment
chemical_list: D000906:Antibodies; D010455:Peptides; D056949:Phototropins; D002118:Calcium
keywords: Avoidance response of chloroplasts; blue-light response; chloroplast de-anchoring; cytoplasmic calcium; phototropin