title: Rapid dark repression of 5-aminolevulinic acid synthesis in green barley leaves.
abstract: In photosynthetic organisms chlorophyll and heme biosynthesis is tightly regulated at various levels in response to environmental adaptation and plant development. The formation of 5-aminolevulinic acid (ALA) is the key regulatory step and provides adequate amounts of the common precursor molecule for the Mg and Fe branches of tetrapyrrole biosynthesis. Pathway control prevents accumulation of metabolic intermediates and avoids photo-oxidative damage. In angiosperms reduction of protochlorophyllide (Pchlide) to chlorophyllide is catalyzed by the light-dependent NADPH:Pchlide oxidoreductase (POR). Although a correlation between down-regulated ALA synthesis and accumulation of Pchlide in the dark was proposed a long time ago, the time-resolved mutual dependency has never been analyzed. Taking advantage of the high metabolic activity of young barley (Hordeum vulgare L.) seedlings, in planta ALA synthesis could be determined with high time-resolution. ALA formation declined immediately after transition from light to dark and correlated with an immediate accumulation of POR-bound Pchlide within the first 60 min in darkness. The flu homologous barley mutant tigrina d(12) uncouples ALA synthesis from dark-suppression and continued to form ALA in darkness without a significant change in synthesis rate in this time interval. Similarly, inhibition of protoporphyrinogen IX oxidase by acifluorfen resulted in a delayed accumulation of Pchlide during the entire dark period and a weak repression of ALA synthesis in darkness. Moreover, it is demonstrated that dark repression of ALA formation relies rather on rapid post-translational regulation in response to accumulating Pchlide than on changes in nuclear gene expression.
authors.affiliation: Humboldt University Berlin, Institute of Biology, Department of Plant Physiology, Unter den Linden 6, D-10099 Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
authors.forename: Enrico
authors.initials: E
authors.lastname: Peter
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Pörs
authors.forename: Stephan
authors.initials: S
authors.lastname: Lorenzen
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
authors.forename: Olaf
authors.initials: O
authors.lastname: Czarnecki
mesh_terms: D000622:Aminolevulinic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D003624:Darkness; D006418:Heme / Q000378:metabolism; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D015227:Lipid Peroxidation; D009579:Nitrobenzoates; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D011521:Protochlorophyllide / Q000096:biosynthesis*; D050768:Protoporphyrinogen Oxidase / Q000378:metabolism; D018749:RNA, Plant / Q000032:analysis
chemical_list: D009579:Nitrobenzoates; D018749:RNA, Plant; D011521:Protochlorophyllide; D006418:Heme; D000622:Aminolevulinic Acid; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D050768:Protoporphyrinogen Oxidase; C018425:acifluorfen