title: Elucidating the role of transport processes in leaf glucosinolate distribution.
abstract: In Arabidopsis (Arabidopsis thaliana), a strategy to defend its leaves against herbivores is to accumulate glucosinolates along the midrib and at the margin. Although it is generally assumed that glucosinolates are synthesized along the vasculature in an Arabidopsis leaf, thereby suggesting that the margin accumulation is established through transport, little is known about these transport processes. Here, we show through leaf apoplastic fluid analysis and glucosinolate feeding experiments that two glucosinolate transporters, GTR1 and GTR2, essential for long-distance transport of glucosinolates in Arabidopsis, also play key roles in glucosinolate allocation within a mature leaf by effectively importing apoplastically localized glucosinolates into appropriate cells. Detection of glucosinolates in root xylem sap unambiguously shows that this transport route is involved in root-to-shoot glucosinolate allocation. Detailed leaf dissections show that in the absence of GTR1 and GTR2 transport activity, glucosinolates accumulate predominantly in leaf margins and leaf tips. Furthermore, we show that glucosinolates accumulate in the leaf abaxial epidermis in a GTR-independent manner. Based on our results, we propose a model for how glucosinolates accumulate in the leaf margin and epidermis, which includes symplasmic movement through plasmodesmata, coupled with the activity of putative vacuolar glucosinolate importers in these peripheral cell layers.
authors.affiliation: Danish National Research Foundation Center for Dynamic Molecular Interactions (S.R.M., H.H.N.-E., B.A.H.) and Department of Plant and Environmental Sciences, Faculty of Science (S.R.M., C.E.O., H.H.N.-E., B.A.H.), University of Copenhagen, DK-1871 Frederiksberg C, Denmark.
authors.forename: Svend Roesen
authors.initials: SR
authors.lastname: Madsen
authors.affiliation: Danish National Research Foundation Center for Dynamic Molecular Interactions (S.R.M., H.H.N.-E., B.A.H.) and Department of Plant and Environmental Sciences, Faculty of Science (S.R.M., C.E.O., H.H.N.-E., B.A.H.), University of Copenhagen, DK-1871 Frederiksberg C, Denmark.
authors.forename: Carl Erik
authors.identifier: http://orcid.org/0000-0002-2275-0956
authors.initials: CE
authors.lastname: Olsen
authors.affiliation: Danish National Research Foundation Center for Dynamic Molecular Interactions (S.R.M., H.H.N.-E., B.A.H.) and Department of Plant and Environmental Sciences, Faculty of Science (S.R.M., C.E.O., H.H.N.-E., B.A.H.), University of Copenhagen, DK-1871 Frederiksberg C, Denmark.
authors.forename: Hussam Hassan
authors.identifier: http://orcid.org/0000-0001-6660-0509
authors.initials: HH
authors.lastname: Nour-Eldin
authors.affiliation: Danish National Research Foundation Center for Dynamic Molecular Interactions (S.R.M., H.H.N.-E., B.A.H.) and Department of Plant and Environmental Sciences, Faculty of Science (S.R.M., C.E.O., H.H.N.-E., B.A.H.), University of Copenhagen, DK-1871 Frederiksberg C, Denmark bah@plen.ku.dk.
authors.forename: Barbara Ann
authors.identifier: http://orcid.org/0000-0002-3742-702X
authors.initials: BA
authors.lastname: Halkier
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D055786:Gene Knockout Techniques; D005961:Glucosinolates / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D019441:Plant Epidermis / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D031425:Plasmodesmata / Q000378:metabolism; D052584:Xylem / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C575185:GTR1 protein, Arabidopsis; C575186:GTR2 protein, Arabidopsis; D005961:Glucosinolates; D009004:Monosaccharide Transport Proteins