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Our basic technology: positron emitting radiotracers


Benefits

Tracer can be detected non-invasively due to the high energy of the decay products which can penetrate through many cm of plant tissue or from roots through soil. Tracer can be administered repeatedly, because the isotopes are short-lived and repeated doses do not accumulate. Experiments can use multiple tracers to study a variety of physiological traits in an individual plant, or repeated measures for longitudinal studies, for example to follow a developmental time course, or to follow the response to stress. Perhaps most important, positron-emitting tracers can be administered at concentrations 3-4 orders of magnitude lower than other radioisotopes (e.g., carbon-14), at true tracer levels without disturbing the biochemical or hormonal homeostasis in the plant.

Isotope Production

The positron emitting radioisotopes are produced in a cyclotron and then converted to desired chemical forms for use in plants. Because of their short half-life, the isotopes must be produced where they are used, and this is the main reason—apart from cost—that they have been used so little in plant science, and in only a handful of locations worldwide. BNL is home to two cyclotrons, the Ebco TR-19 and JSW cyclotrons.

 


Integrated Plant Radiotracer Laboratory

The BNL facility is unique in that it combines standardization of technology offering parallel tracer studies and system automation enabling turn-key operation that is appealing to plant biologists.

Carbon-11 administered to plant leaves as 11CO2 is a mainstay for tracing carbon recently assimilated through photosynthesis, and can be incorporated into a variety of carbon-based biomolecules by specialized rapid chemical syntheses. Our group has developed a suite of radiometric bioassays for measuring carbon fluxes into a number of metabolite pools. Many of these assays have been adapted to higher throughput screening. By measuring the 11C/12C isotopic signature in metabolites we can determine how “new” carbon (recently fixed as 11CO2) is being utilized by the plant.

Through complex organic radiochemistry carried out in hot cells,carbon-11 can be attached to biomolecules of interest and most particularly to plant hormones. For example, indole-3-acetic acid (auxin) and several of its biosynthetic precursors have been radiolabeled and used to measure auxin biosynthesis and metabolism, and image its transport in intact plants.

Nitrogen has only one radioisotope, 13N, which can be used as di-nitrogen, N2 (e.g., for legume studies), as nitrate and ammonium (NO3-, NH4+) for uptake studies, and as ammonia gas (NH3)

 



for studies of amino acid metabolism and transport. Just as CO2 is the substrate for plant carbon assimilation (via Rubisco), nitrate is reduced to ammonia, and ammonia is the substrate for amino acid synthesis. Labeled ammonia gas at high specific activity, can be supplied to leaves at a very low concentration with little to no physiological effect, offering a way to infuse a radioactive probe into the plant’s nitrogen metabolic pathways.

Imaging Capabilities

Radiotracer residing within the plant’s tissues/organs is detected via its decay products—either the positrons directly or subsequent annihilation photons.

  • Autoradiography of a plant gives a snapshot of tracer location, by detecting the positrons. It is suitable for experiments where the small disturbance necessary to move the plant to an imaging bed, or to cover the tissue with the imaging plate for several minutes, is acceptable.
  • Dynamic studies utilize the annihilation gamma photons, by coincidence detection, or by positron emission tomography.

 

Summary of Core Capabilities


 

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Last Modified: February 14, 2013
Please forward all questions about this site to: Kathy Folkers