title: Actin cytoskeleton in Arabidopsis thaliana under blue and red light.
abstract: BACKGROUND
  Actin cytoskeleton is the basis of chloroplast-orientation movements. These movements are activated by blue light in the leaves of terrestrial angiosperms. Red light has been shown to affect the spatial reorganization of F-actin in water plants, where chloroplast movements are closely connected with cytoplasmic streaming. The aim of the present study was to determine whether blue light, which triggers characteristic responses of chloroplasts, i.e. avoidance and accumulation, also influences F-actin organization in the mesophyll cells of Arabidopsis thaliana. Actin filaments in fixed mesophyll tissue were labelled with Alexa Fluor 488-conjugated phalloidin. The configuration of actin filaments, expressed as a form factor (4 pi x area/perimeter(2)), was determined for all actin formations which were measured in fluorescence confocal images.
  
  
  RESULTS
  In the present study, we compare form-factor distributions and the median form factors for strong and weak, blue- and red-irradiated tissues. Spatial organization of the F-actin network did not undergo any changes which could be attributed specifically to blue light. Actin patterns were similar in blue-irradiated wild-type plants and phot2 (phototropin 2) mutants which lack the avoidance response of chloroplasts. However, significant differences in the shape and distribution of F-actin formations were observed between mesophyll cells of phot2 mutants irradiated with strong and weak red light. These differences were absent in wild-type leaves.
  
  
  CONCLUSIONS
  Actin does not appear to be the main target for the blue-light chloroplast-orientation signal. The modes of actin involvement in chloroplast translocations are different in water and terrestrial angiosperms. The results suggest that co-operation occurs between blue- and red-light photoreceptors in the control of the actin cytoskeleton architecture in Arabidopsis.
authors.affiliation: Department of Plant Physiology and Biochemistry, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, Krakow, Poland.
authors.forename: Weronika
authors.initials: W
authors.lastname: Krzeszowiec
authors.forename: Bartek
authors.initials: B
authors.lastname: Rajwa
authors.forename: Jurek
authors.initials: J
authors.lastname: Dobrucki
authors.forename: Halina
authors.initials: H
authors.lastname: Gabryś
mesh_terms: D000199:Actins / Q000378:metabolism*; D017360:Arabidopsis / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism* / Q000528:radiation effects*; D021621:Imaging, Three-Dimensional; D008027:Light; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; C514696:UBC24 protein, Arabidopsis; D044763:Ubiquitin-Conjugating Enzymes