title: Active protein transport through plastid tubules: velocity quantified by fluorescence correlation spectroscopy.
abstract: Dynamic tubular projections emanate from plastids in certain cells of vascular plants and are especially prevalent in non-photosynthetic cells. Tubules sometimes connect two or more different plastids and can extend over long distances within a cell, observations that suggest that the tubules may function in distribution of molecules within, to and from plastids. In a new application of two-photon excitation (2PE) fluorescence correlation spectroscopy (FCS), we separated diffusion of fluorescent molecules from active transport in vivo. We quantified the velocities of diffusion versus active transport of green fluorescent protein (GFP) within plastid tubules and in the cytosol in vivo. GFP moves by 3-dimensional (3-D) diffusion both in the cytosol and plastid tubules, but diffusion in tubules is about 50 times and 100 times slower than in the cytosol and an aqueous solution, respectively. Unexpectedly larger GFP units within plastid tubules exhibited active transport with a velocity of about 0.12 microm/second. Active transport might play an important role in the long-distance distribution of large numbers of molecules within the highly viscous stroma of plastid tubules.
authors.affiliation: Department of Molecular Biology and Genetics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Köhler
authors.forename: P
authors.initials: P
authors.lastname: Schwille
authors.forename: W W
authors.initials: WW
authors.lastname: Webb
authors.forename: M R
authors.initials: MR
authors.lastname: Hanson
mesh_terms: D000595:Amino Acid Sequence; D001693:Biological Transport, Active / Q000187:drug effects; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004058:Diffusion; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D018087:Plastids / Q000378:metabolism*; D021381:Protein Transport; D011938:Rec A Recombinases / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence / Q000379:methods; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism
chemical_list: D008164:Luminescent Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D011938:Rec A Recombinases