Om insoluble Fe sources at higher pH (Rodr uezCelma et al Schmid et al Schmidt et al), root exudates are unable to solubilize Fe from insoluble Fe sources, and supplementation on the agarose development media with scopoletin, esculetin or esculin restores the Fesufficient phenotype (Schmid et al).Having said that, in in vitro tests only esculetin (using a catechol moiety), was located to mobilize Fe(III) from an Fe(III) oxide source at higher pH (Schmid et al).The secretion of coumarins by Fedeficient roots entails an ABC (ATPbinding cassette) transporter, ABCGPDR, which is strongly overexpressed in plants grown in media deprived of Fe (Yang et al Fourcroy et al ,) or containing insoluble Fe(III) at high pH (Rodr uezCelma et al).The export of scopoletin, fraxetin, isofraxidin, and an isofraxidin isomer was considerably impaired in the mutant abcg (Fourcroy et al), which, as it happens with f h, is inefficient in taking up Fe from insoluble Fe(III) at pH .(Rodr uezCelma et al).The root secretion of fluorescent phenolic 3,5-Diiodothyropropionic acid Purity & Documentation compounds in a.thaliana also demands the Fe deficiencyinducible glucosidase BGLU (Zamioudis et al).Alternatively, the IRTFRO highaffinity root Fe uptake technique is important for the plant to take up Fe as soon as mobilized, since irt and fro plants grown with unavailable Fe and in presenceFrontiers in Plant Science www.frontiersin.orgNovember Volume ArticleSisTerraza et al.Coumarins in FeDeficient Arabidopsis PlantsFIGURE Chemical structures of a few of the phenolic compounds cited within this study.The plant compounds involve coumarins and their glucosides (A), coumarin precursors and monolignols (B) and coumarinolignans derived in the coumarin fraxetin (C).The fraxetin moiety is highlighted in blue inside the coumarinolignan structures.Compounds utilised as internal requirements (D) consist of a methylenedioxycoumarin and a lignan.of phenolics create chlorosis (Fourcroy et al).The coregulation of ABCG and coumarin synthesis genes with Match, IRT, FRO and AHA (Rodr uezCelma et al) as well as the requirement of Match for F’H upregulation upon Fe deficiency (Schmid et al) help that all these components act inside a coordinated mode.Limitations inherent towards the analytical procedures applied andor troubles in compound structure elucidation have prevented the full characterization in the adjustments in coumarin composition promoted by Fe deficiency.1st, HPLC coupled to fluorescence detection and mass spectrometry (MS and MSn) identification was made use of, thus focusing only on fluorescent coumarin compounds changing in response to Fe deficiency (Fourcroy et al); a equivalent approach was taken later on by Schmid et al..Inside a second strategy, the usage of full chromatographic MS profiles permitted the detection of dozens of compounds changing with Fe deficiency, but only exactly the same coumarins already found using the fluorescence detection approach may very well be identified (Schmidt et al ).The aim of this study was to gain insight in to the phenolic composition of A.thaliana root exudates in response to Fe deficiency, a vital step for any thorough understanding of the function of phenolics in plant Fe acquisition.Root extracts and exudates from Fesufficient and Fedeficient A.thaliana plants grown at pH .and .have been analyzed by HPLC coupled to five different detectors fluorescence, photodiode array, MStime of flight (TOF), MSion trap and MSMS tandem quadrupole (Q)TOF, and identification and quantification of phenolics wasFrontiers in Plant Science www.frontiersin.orgNovember PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/21542743 Volum.