Single and Combined Fe and S Deficiency Differentially Modulate Root Exudate Composition in Tomato: A Double Strategy for Fe Acquisition?

Fe chlorosis is considered as one of the major constraints on crop growth and yield
worldwide, being particularly worse when associated with S shortage, due to the tight link between
Fe and S. Plant adaptation to inadequate nutrient availabilities often relies on the release of root
exudates that enhance nutrients, mobilization from soil colloids and favour their uptake by roots. This
work aims at characterizing the exudomic profile of hydroponically grown tomato plants subjected
to either single or combined Fe and S deficiency, as well as at shedding light on the regulation
mechanisms underlying Fe and S acquisition processes by plants. Root exudates have been analysed
by untargeted metabolomics, through liquid chromatography–mass spectrometry as well as gas
chromatography–mass spectrometry following derivatization. More than 200 metabolites could be
putatively annotated. Venn diagrams show that 23%, 10% and 21% of dierential metabolites are
distinctively modulated by single Fe deficiency, single S deficiency or combined Fe–S deficiency,
respectively. Interestingly, for the first time, a mugineic acid derivative is detected in dicot plants root
exudates. The results seem to support the hypothesis of the co-existence of the two Fe acquisition
strategies in tomato plants.