Three-Dimensional Positron Emission Tomography/Computed Tomography Analysis of ¹³NO₃⁻ Uptake and ¹³N Distribution in Growing Kohlrabi

We report the application of three-dimensional positron emission tomography/computed tomography (PET/CT) for the analysis of ¹³NO₃⁻ uptake and ¹³N distribution in growing kohlrabi. The analytical procedures, equipment parameters, and image reconstruction mode for plant imaging were tested and selected. ¹³N in growing kohlrabi plants was imaged versus time using both PET movies and PET/CT tomograms. The ¹³NO₃⁻ transport velocity in kohlrabi from root to petiole was estimated to be 1.0 cm/min. The appearance of shell-shaped ¹³NO₃⁻ transport pathways, corresponding to the kohlrabi corm, suggests the existence of special routes with higher efficiency for ¹³NO₃⁻ transport, which tends to have the shortest distances to the leaves or buds. Standardized uptake values (SUVs), used as the representative figures for describing ¹³N distribution, were quantified versus time at some putative sites of interest. For multiple analysis of the same-plant, ¹³N distribution in kohlrabi under normal conditions, methionine sulfoximine (MSX) stress, and recovery from MSX stress was examined. The ¹³N distribution variation studies were also done under the above three growth conditions. Our results suggest a significant downregulation of nitrate uptake in kohlrabi in the presence of MSX.