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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 many cm of plant and soil);

Tracer can be administered repeatedly (because the isotopes are short-lived and repeated doses do not accumulate). Experiments are designed show the timing and sequence of events in different parts of the plant, after diagnostic treatments.

Tracer Production

BNL’s Japan Steel Works 41-in. “baby cyclotron”.

The positron emitting radionuclides of carbon or nitrogen, with half-lives of 20.4 and 10.0 min, are produced in a cyclotron and converted to the required chemical form for use with 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 3 locations in the world.

Carbon. Carbon-11 dioxide is a mainstay for tracing recently photo-assimilated carbon, but we also synthesize other chemicals: for example radioligands which allow imaging of metabolism, transport and receptor binding associated with the ligand. Phytoremediation of chlorocarbons is investigated with the help of 11C-radiolabeled pollutant.

Nitrogen has only one radioisotope, 13N, which can be used as di-nitrogen, N2 (eg 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 is supplied at high specific activity, ie a very low concentration, with little to no physiological effect.

Detection

Chemistry is carried out in lead shielded “hot-cells” that protect us from radiation.

Tracer in the plant is detected via its decay products—either the positrons 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, is acceptable.
• Dynamic studies utilize the annihilation gamma photons, detected with appropriate radiation shielding to restrict measurement to specific regions of the plant, by coincidence detection, or by positron emission tomography.
• Volatile organic compounds (VOC) can be trapped for detection of radiolabeled compounds.

Last Modified: February 1, 2008

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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