title: Antisense reduction of serine hydroxymethyltransferase results in diurnal displacement of NH4+ assimilation in leaves of Solanum tuberosum.
abstract: Serine hydroxymethyltransferase (SHMT) is part of the mitochondrial enzyme complex catalysing the photorespiratory production of serine, ammonium and CO(2) from glycine. Potato plants (Solanum tuberosum cv. Solara) with antisensed SHMT were generated to investigate whether photorespiratory intermediates accumulated during light lead to nocturnal activation of the nitrogen-assimilating enzymes glutamine synthetase (GS) and glutamate synthase (GOGAT). The transformant lines contained 70-90% less SHMT protein, and exhibited a corresponding decrease in mitochondrial SHMT activity. SHMT antisense plants displayed lower photosynthetic capacity and accumulated glycine in light. Glycine was converted to serine in the second half of the light period, while serine, ammonium and glutamine showed an inverse diurnal rhythm and reached highest values in darkness. GS/GOGAT protein levels and activities in the transgenics also reached maximum levels in darkness. The diurnal displacement of NH(4)(+) assimilation was accompanied by a change in the subunit composition of GS(2), but not GS(1). It is concluded that internal accumulation of post-photorespiratory ammonium is leading to nocturnal activation of GS/GOGAT, and that the time shift in ammonia assimilation can constitute part of a strategy to survive photorespiratory impairment.
authors.affiliation: Plant and Soil Science Laboratory, Department of Agricultural Sciences, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark. jks@kvl.dk
authors.forename: Jan K
authors.initials: JK
authors.lastname: Schjoerring
authors.forename: Gisela
authors.initials: G
authors.lastname: Mäck
authors.forename: Kent Høier
authors.initials: KH
authors.lastname: Nielsen
authors.forename: Søren
authors.initials: S
authors.lastname: Husted
authors.forename: Akira
authors.initials: A
authors.lastname: Suzuki
authors.forename: Simon
authors.initials: S
authors.lastname: Driscoll
authors.forename: Ralf
authors.initials: R
authors.lastname: Boldt
authors.forename: Hermann
authors.initials: H
authors.lastname: Bauwe
mesh_terms: D000596:Amino Acids / Q000096:biosynthesis; D002245:Carbon Dioxide / Q000378:metabolism; D002940:Circadian Rhythm; D003624:Darkness; D012696:Glycine Hydroxymethyltransferase / Q000235:genetics / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000235:genetics*; D018515:Plant Leaves / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D011198:Solanum tuberosum / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D016376:Oligonucleotides, Antisense; D000644:Quaternary Ammonium Compounds; D002245:Carbon Dioxide; D012696:Glycine Hydroxymethyltransferase