Authors:
Fabio Trevisan | Free University of Bolzano, Faculty of Agricultural, Environmental and Food Sciences | Italy
Dr. Raphael Tiziani | Free University of Bolzano, Faculty of Agricultural, Environmental and Food Sciences | Italy
Dr. Ondˇrej Hodek | Swedish University of Agricultural Sciences, Swedish Metabolomics Centre, Department of Forest Genetics and Plant Physiology | Sweden
Prof. Thomas Moritz | Swedish University of Agricultural Sciences, Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology & University of Copenhagen, Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences | Denmark
Prof. Sandra Jämtgård | Swedish University of Agricultural Sciences, Department of Forest Ecology and Management | Sweden
Prof. Stefano Cesco | Free University of Bolzano, Faculty of Agricultural, Environmental and Food Sciences | Italy
Prof. Tanja Mimmo | Free University of Bolzano, Faculty of Agricultural, Environmental and Food Sciences & Competence Centre of Plant Health | Italy
Phosphorus (P) and iron (Fe) deficiencies trigger plant root exudation of carboxylates like citrate, which facilitates nutrient uptake but requires extra energy. Thus, reacquiring exudates could be an energy-saving strategy for plants. The reuptake of citrate was demonstrated in nutrient-sufficient and P-deficient plants, but no information about Fe deficiency nor about the metabolic fate of citrate taken up by roots is available. We hypothesise that P and Fe deficiencies will trigger and enhance citrate root uptake and translocation to shoots, while its metabolization will differ depending on the plant nutrient status. Tomato seedlings grown hydroponically in Control, -Fe and -P conditions were sampled twice a week for 2 weeks. The δ13C was measured in roots and shoots after a 2h root exposure to 13C labelled citrate (0, 50 or 500 µmol L-1) by IRMS. During the last sampling, tomato plants were exposed for 15, 30, 60 and 120 min to 0 and 500 µmol L-1 13C labelled citrate and quenched in liquid nitrogen for Compound Specific Isotope Analysis (CSIA) by LC-qTOF. Phosphorus and Fe deficiencies enhanced citrate uptake and translocation. The uptaken citrate was utilized in the TCA cycle in all treatments, while -P plants showed a 13C enrichment also in the GABA shunt and GS-GOGAT pathways and -Fe plants in the Urea pathway. Depending on the nutrient status, the uptaken citrate was metabolized differently. This highlights the potential of citrate root uptake to sustain important functions in nutrient-deficient plants. This study confirmed citrate reacquisition and translocation, revealing the intricate roles of nutrient deficiency in these processes and unravelling for the first time the metabolic fate of root-acquired citrate.