title: Blue light-dependent changes in loosely bound calcium in Arabidopsis mesophyll cells: an X-ray microanalysis study.
abstract: Calcium is involved in the signal transduction pathway from phototropins, the blue light photoreceptor kinases which mediate chloroplast movements. The chloroplast accumulation response in low light is controlled by both phot1 and phot2, while only phot2 is involved in avoidance movement induced by strong light. Phototropins elevate cytosolic Ca(2+) after activation by blue light. In higher plants, both types of chloroplast responses depend on Ca(2+), and internal calcium stores seem to be crucial for these processes. Yet, the calcium signatures generated after the perception of blue light by phototropins are not well understood. To characterize the localization of calcium in Arabidopsis mesophyll cells, loosely bound (exchangeable) Ca(2+) was precipitated with potassium pyroantimonate and analyzed by transmission electron microscopy followed by energy-dispersive X-ray microanalysis. In dark-adapted wild-type Arabidopsis leaves, calcium precipitates were observed at the cell wall, where they formed spherical structures. After strong blue light irradiation, calcium at the apoplast prevailed, and bigger, multilayer precipitates were found. Spherical calcium precipitates were also detected at the tonoplast. After red light treatment as a control, the precipitates at the cell wall were smaller and less numerous. In the phot2 and phot1phot2 mutants, calcium patterns were different from those of wild-type plants. In both mutants, no elevation of calcium after blue light treatment was observed at the cell periphery (including the cell wall and a fragment of cytoplasm). This result confirms the involvement of phototropin2 in the regulation of Ca(2+) homeostasis in mesophyll cells.
authors.affiliation: Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland Malopolska Centre of Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Justyna
authors.initials: J
authors.lastname: Łabuz
authors.affiliation: Laboratory of Electron and Confocal Microscopy, Faculty of Biology, Adam Mickiewicz University, Poznań, Poland.
authors.forename: Sławomir
authors.initials: S
authors.lastname: Samardakiewicz
authors.affiliation: Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Paweł
authors.initials: P
authors.lastname: Hermanowicz
authors.affiliation: Laboratory of Electron Microscopy, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Elżbieta
authors.initials: E
authors.lastname: Wyroba
authors.affiliation: Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Maria
authors.initials: M
authors.lastname: Pilarska
authors.affiliation: Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland halina.gabrys@uj.edu.pl.
authors.forename: Halina
authors.initials: H
authors.lastname: Gabryś
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D004577:Electron Probe Microanalysis; D008027:Light; D058503:Mesophyll Cells / Q000378:metabolism*
chemical_list: D002118:Calcium
keywords: Arabidopsis; blue light; calcium signaling; chloroplast movements; mesophyll cells; phototropin2.; thaliana