Comparing 2-[18F]fluoro-2-deoxy-D-glucose and [68Ga]gallium-citrate translocation in Arabidopsis thaliana

2-[18F]fluoro-2-deoxy-D-glucose (18FDG) is a glucose surrogate commonly used in clinical or animal imaging but rarely in plant imaging to trace glucose metabolism. Recently, 18FDG has been employed in plant imaging for studying photoassimilate translocation and glycoside biosynthesis. There is growing evidence that 18FDG could be used as a tracer in plant imaging studies to trace sugar dynamics. However, to confirm this hypothesis, it was necessary to show that the observed 18FDG distribution in an intact plant is an outcome of the chemical nature of the introduced radiotracer and not of the plant vascular architecture or radiotracer introduction method.MethodsIn the present work, we fed 18FDG and [68Ga]gallium-citrate (68Ga-citrate) solution through mature Arabidopsis thaliana leaf and monitored subsequent radioactivity distribution using positron autoradiography. The possible route of radioactivity translocation was elucidated through stem-girdling experiments. We also employed a bi-functional positron emission tomography/computed tomography (PET/CT) modality to capture 18FDG radiotracer dynamics in one of the plants in order to assess applicability of PET/CT for 4-D imaging in an intact plant.ResultsAutoradiography results showed that [18F] radioactivity accumulated mostly in roots and young growing parts such as the shoot apex, which are known to act as sinks for photoassimilate. [18F] radioactivity translocation, in this case, occurred mainly via phloem. PET/CT results corroborated with autoradiography. [68Ga] radioactivity, on the other hand, was mainly translocated to neighboring leaves and its translocation occurred via both xylem and phloem.ConclusionThe radioactivity distribution pattern and translocation route observed after 18FDG feeding is markedly different from that of 68Ga-citrate. [18F] radioactivity distribution pattern in an intact plant is found similar to the typical distribution pattern of photoassimilates. Despite its limitations in quantification and resolution, PET/CT could be a useful tool to elucidate in vivo dynamics of [18F] radioactivity in intact plants.