title: Mathematical modeling of positron emission tomography (PET) data to assess radiofluoride transport in living plants following petiolar administration.
abstract: BACKGROUND
  Ion transport is a fundamental physiological process that can be studied non-invasively in living plants with radiotracer imaging methods. Fluoride is a known phytotoxic pollutant and understanding its transport in plants after leaf absorption is of interest to those in agricultural areas near industrial sources of airborne fluoride. Here we report the novel use of a commercial, high-resolution, animal positron emission tomography (PET) scanner to trace a bolus of [(18)F]fluoride administered via bisected petioles of Brassica oleracea, an established model species, to simulate whole plant uptake of atmospheric fluoride. This methodology allows for the first time mathematical compartmental modeling of fluoride transport in the living plant. Radiotracer kinetics in the stem were described with a single-parameter free- and trapped-compartment model and mean arrival times at different stem positions were calculated from the free-compartment time-activity curves.
  
  
  RESULTS
  After initiation of administration at the bisected leaf stalk, [(18)F] radioactivity climbed for approximately 10 minutes followed by rapid washout from the stem and equilibration within leaves. Kinetic modeling of transport in the stem yielded a trapping rate of 1.5 +/- 0.3%/min (mean +/- s.d., n = 3), velocity of 2.2 +/- 1.1 cm/min, and trapping fraction of 0.8 +/- 0.5%/cm.
  
  
  CONCLUSIONS
  Quantitative assessment of physiologically meaningful transport parameters of fluoride in living plants is possible using standard positron emission tomography in combination with petiolar radiotracer administration. Movement of free fluoride was observed to be consistent with bulk flow in xylem, namely a rapid and linear change in position with respect to time. Trapping, likely in the apoplast, was observed. Future applications of the methods described here include studies of transport of other ions and molecules of interest in plant physiology.
authors.affiliation: T123 Waisman Center, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Alexander K
authors.initials: AK
authors.lastname: Converse
authors.affiliation: T123 Waisman Center, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Elizabeth O
authors.initials: EO
authors.lastname: Ahlers
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Tom W
authors.initials: TW
authors.lastname: Bryan
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Jackson D
authors.initials: JD
authors.lastname: Hetue
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Lake
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Ellison
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Engle
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Todd E
authors.initials: TE
authors.lastname: Barnhart
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Nickles
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Williams
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA.
authors.forename: Onofre T
authors.initials: OT
authors.lastname: DeJesus
keywords: Brassica oleracea; Ion transport; Kinetic modeling; Positron emission tomography; Radiotracer