Exploring the transport of plant metabolites using positron emitting radiotracers

Abstract

Short-lived positron-emitting radiotracer techniques provide time-dependent data that are critical for developing models of metabolite transport and resource distribution in plants and their microenvironments. Until recently these techniques were applied to measure radiotracer accumulation in coarse regions along transport pathways. The recent application of positron emission tomography (PET) techniques to plant research allows for detailed quantification of real-time metabolite dynamics on previously unexplored spatial scales. PET provides dynamic information with millimeter-scale resolution on labeled carbon, nitrogen, and water transport over a small plant-size field of view. Because details at the millimeter scale may not be required for all regions of interest, hybrid detection systems that combine high-resolution imaging with other radiotracer counting technologies offer the versatility needed to pursue wide-ranging plant physiological and ecological research. In this perspective we describe a recently developed hybrid detection system at Duke University that provides researchers with the flexibility required to carry out measurements of the dynamic responses of whole plants to environmental change using short-lived radiotracers. Following a brief historical development of radiotracer applications to plant research, the role of radiotracers is presented in the context of various applications at the leaf to the whole-plant level that integrates cellular and subcellular signals andor controls.

Imaging of photoassimilates transport in plant tissues by positron emission tomography

“…labelled molecules with positron emitters, are absorbed via normal metabolism and distributed throughout the plant body. In vivo PET analysis involves the γ-rays detection after annihilation process of an emitted positron with a nearby electron producing two 511 keV photons and enables to track the transport and distribution of the radiotracers in the plant as a function of time (Kiser et al 2008). For plant biologists, the advantages of PET systems mainly include the capability of providing real-time dynamic images of positron-emitting isotopes or the movement of labelled molecules under in vivo conditions without damage to the plants, the possibility to obtain 3D images, and measurements in absolute units of radioactivity with high precision.…”

Plant-PET Scans: In Vivo Mapping of Xylem and Phloem Functioning

“…Voxel: the 3D counterpart of a pixel. may contribute significantly [25,[36][37][38][39][40][41][42][43] (Figure 2). This short-lived isotope can be widely used because of the presence of carbon in many plant molecules.…”

“…These isotopes have a short half-life (t 1/2 ), which makes them ideal for studying short-term processes (minutes to hours) because of their high signal output during the short time-period they exist. The downside is that positrons travel only a small distance before they annihilate (Table 1 and Figure 1A), which fundamentally limits the maximum attainable resolution of PET [25,39,49,82,83].…”

“…PET is based on coincident detection of antiparallel g-rays (1808) with an energy of 511 keV, produced by the annihilation of an electron (e À ) and a positron (b + ), the latter being emitted by a short-lived radionuclide tracer upon decay ( Figure 1A) [21,81]. The most important short-lived radionuclides used in biological studies are 11 C, 13 N, 15 O, and 18 F (Table 1) [21,25,80]. These isotopes have a short half-life (t 1/2 ), which makes them ideal for studying short-term processes (minutes to hours) because of their high signal output during the short time-period they exist.…”

“…PET is a non-invasive and in vivo functional imaging technique that, when applied with plants, produces a 3D image of transport and distribution in the vascular tissues [25,39,80]. PET is based on coincident detection of antiparallel g-rays (1808) with an energy of 511 keV, produced by the annihilation of an electron (e À ) and a positron (b + ), the latter being emitted by a short-lived radionuclide tracer upon decay ( Figure 1A) [21,81].…”