AUTHOR=Hubeau Michiel , Mincke Jens , Vanhove Christian , Gorel Anaïs Pasiphaé , Fayolle Adeline , Epila Jackie , Leroux Olivier , Vandenberghe Stefaan , Steppe Kathy TITLE=11C-Autoradiographs to Image Phloem Loading JOURNAL=Frontiers in Forests and Global Change VOLUME=2 YEAR=2019 URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2019.00020 DOI=10.3389/ffgc.2019.00020 ISSN=2624-893X ABSTRACT=

Generally, tree species load photoassimilates passively into the phloem, while herbaceous species load actively. These phloem loading strategies have implications for phloem sugar concentration and growth potential. Whereas, in previous research, phloem loading identification was performed with ¹⁴C-autoradiography, we suggest ¹¹C-autoradiography, because of its compatibility with plant-PET (positron emission tomography) scans. Because ¹¹C-autoradiography has been hardly used in plant sciences so far, it was tested in contrasting plant species: one temperate tree species, Populus tremula L., three tropical tree species, Erythrophleum suaveolens (Guill. & Perr.) Brenan, E. ivorense A. Chev., and Maesopsis eminii Engl., and two herbaceous crop species Solanum lycopersicum L. and S. tuberosum L. Our results confirmed that P. tremula is a passive loader, and Solanum spp. are active loaders. Erythrophleum spp. and young leaves of M. eminii showed the expected passive loading strategy, but the mature leaves of M. eminii showed an uncommon pattern. Images corrected for leaf tissue thickness supported that mature leaves of M. eminii used active phloem loading, which is linked to continuous investment in growth and new leaves, supporting the lower carbon storage levels often observed in tropical tree species. With this study, we demonstrate that ¹¹C-autoradiography is a powerful tool to acquire detailed tracer distribution in leaves to typify phloem loading strategies in plant species.