title: Decreased capacity for sodium export out of Arabidopsis chloroplasts impairs salt tolerance, photosynthesis and plant performance.
abstract: Salt stress is a widespread phenomenon, limiting plant performance in large areas around the world. Although various types of plant sodium/proton antiporters have been characterized, the physiological function of NHD1 from Arabidopsis thaliana has not been elucidated in detail so far. Here we report that the NHD1-GFP fusion protein localizes to the chloroplast envelope. Heterologous expression of AtNHD1 was sufficient to complement a salt-sensitive Escherichia coli mutant lacking its endogenous sodium/proton exchangers. Transport competence of NHD1 was confirmed using recombinant, highly purified carrier protein reconstituted into proteoliposomes, proving Na(+) /H(+) antiport. In planta NHD1 expression was found to be highest in mature and senescent leaves but was not induced by sodium chloride application. When compared to wild-type controls, nhd1 T-DNA insertion mutants showed decreased biomasses and lower chlorophyll levels after sodium feeding. Interestingly, if grown on sand and supplemented with high sodium chloride, nhd1 mutants exhibited leaf tissue Na(+) levels similar to those of wild-type plants, but the Na(+) content of chloroplasts increased significantly. These high sodium levels in mutant chloroplasts resulted in markedly impaired photosynthetic performance as revealed by a lower quantum yield of photosystem II and increased non-photochemical quenching. Moreover, high Na(+) levels might hamper activity of the plastidic bile acid/sodium symporter family protein 2 (BASS2). The resulting pyruvate deficiency might cause the observed decreased phenylalanine levels in the nhd1 mutants due to lack of precursors.
authors.affiliation: Plant Physiology, University of Kaiserslautern, Erwin Schrödinger Straße, Kaiserslautern, D-67653, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Müller
authors.forename: Hans-Henning
authors.initials: HH
authors.lastname: Kunz
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
authors.forename: Grant
authors.initials: G
authors.lastname: Kemp
authors.forename: Howard S
authors.initials: HS
authors.lastname: Young
authors.forename: H Ekkehard
authors.initials: HE
authors.lastname: Neuhaus
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D018533:Biomass; D015153:Blotting, Western; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology*; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055049:Salt Tolerance / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D017923:Sodium-Hydrogen Exchangers; D002734:Chlorophyll; D012965:Sodium Chloride; D012964:Sodium
keywords: Arabidopsis; membrane protein; plastid; salt tolerance; sodium; transport