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 (13)NO(3)(-) uptake and (13)N distribution in growing kohlrabi. The analytical procedures, equipment parameters, and image reconstruction mode for plant imaging were tested and selected. (13)N in growing kohlrabi plants was imaged versus time using both PET movies and PET/CT tomograms. The (13)NO(3)(-) transport velocity in kohlrabi from root to petiole was estimated to be 1.0 cm/min. The appearance of shell-shaped (13)NO(3)(-) transport pathways, corresponding to the kohlrabi corm, suggests the existence of special routes with higher efficiency for (13)NO(3)(-) transport, which tends to have the shortest distances to the leaves or buds. Standardized uptake values (SUVs), used as the representative figures for describing (13)N distribution, were quantified versus time at some putative sites of interest. For multiple analysis of the same-plant, (13)N distribution in kohlrabi under normal conditions, methionine sulfoximine (MSX) stress, and recovery from MSX stress was examined. The (13)N 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.