Radioisotopes and Nuclear Imaging Help Track Effects of Soil Contaminants

Niels van der Lelie’s team in Brookhaven Lab’s Biology Department is collaborating with scientists in the Chemistry Department to gain a better understanding of how the introduction of contaminant-eating bacteria might alter normal plant function. Their approach uses some of the techniques developed for medical imaging in human and small animal studies to track the allocation of nutrients and other biochemical compounds within the plants.

By administering carbon dioxide labeled with the radioisotope carbon-11 to a single plant leaf (circled), scientists can track the distribution of radioactive sugar derived from that carbon over time, and study how the distribution varies with exposure to challenges such as contaminants. Red shows the highest level of the carbon-11 radiotracer; blue the lowest.

“Since the endophytic bacteria rely on the host plant for most, if not all, of their nutrients, we believe that some of the plant’s resources — including carbohydrates and amino acids — will be reallocated to sustain the energy-consuming biodegradation chemistry carried on by the bacteria,” says chemist Richard Ferrieri.

To monitor these changes, Ferrieri and colleague Michael Thorpe have developed novel techniques to study plant physiology using radiotracers — substances made with short-lived radioactive versions of ordinary chemical elements, such as those used to image brain chemistry. For example, under tightly controlled, closed environmental conditions, the scientists can administer discrete pulses of carbon dioxide gas tagged with radioactive carbon-11 or ammonia gas tagged with radioactive nitrogen-13 directly to leaves on intact plants. They then track the movement and biochemical interactions of the radioactive sugar and amino acids derived from these nutrients using non-invasive imaging techniques such as positron autoradiography and positron emission tomography (PET).

These tools will allow the scientists a unique opportunity to unravel the complex biochemical pathways involved in normal plant functions, including maintaining carbon and nitrogen balances for growth, and to see whether this balance changes over time from exposure to contaminants or the presence of endophytic bacteria.

Because the radiotracers used have very short half-lives (they decay in a matter of minutes), the radioactivity is quickly cleared from the plant. This allows repeated monitoring of the same plant over time. No other techniques afford this opportunity.
Additionally, the team plans to radiolabel key environmental contaminants such as carbon tetrachloride and trichloroethylene, again using carbon-11, to provide a unique look at the dynamics for uptake and transport of contaminants throughout the plant, and to gain greater insight into the mechanisms of biodegradation.

These developments will draw on Brookhaven’s strength as a world-class laboratory in the synthesis of radiotracers. The current work is supported by a seed grant from Brookhaven’s Laboratory Directed Research and Development Program.