Elucidating 2-deoxy-2-fluoro-D-glucose translocation, metabolism, and application in plants
The aim of this thesis was to explore and expand applications of 2-deoxy-2-fluoro-D-glucose (FDG) in plant imaging. In present work, I analyzed FDG translocation and elucidated FDG metabolism in model plant species Arabidopsis. In collaboration with Dr. Meldau, I demonstrated that FDG could be employed as radiotracer to study carbon allocation in Nicotiana upon herbivory. FDG being the glucose analog, it was proposed that FDG could be used as a tracer for photoassimilates. To confirm above hypothesis, I compared radioactivity distribution pattern of two chemically distinct radiotracers, viz. FDG and Ga-citrate. The [18F] and [68Ga] radioactivity distributions were significantly different. [18F] radioactivity distribution pattern was similar to photoassimilates and translocated exclusively via phloem. I also demonstrated that FDG could be employed as a radiotracer for in vivo imaging using positron emission tomography. Further, I analyzed FDG metabolism in Arabidopsis to unravel underlying biochemical pathways. On the basis of exact monoisotopic masses, MS/MS fragmentation, and NMR data; I identified F-gluconic acid, FDG-6-P, F-maltose, and UDP-FDG as end products of FDG metabolism. In plants, FDG was taken up by the cells via HgCl2-sensitive passive uptake process similar to that of glucose. Glycolysis and starch degradation pathway seem to be the important pathways for FDG metabolism in plants. In collaboration with Dr. Meldau, I showed that herbivory increased carbon allocation towards below ground parts such as roots but away from growing parts such as root tips. Experiments with JA-insensitive irCOI1 plant showed that the resultant carbon allocation is dependent upon JA which may be acting in co-ordination with other phytoharmones to regulate plant defense response and plant growth. In conclusion, my thesis provided a basic foundation for establishing FDG as a radiotracer for plant imaging and presents a methodology to trace carbon allocation in plant using FDG.