Journal Article

Rapid Dark Repression of 5-Aminolevulinic Acid Synthesis in Green Barley Leaves

Andreas Richter, Enrico Peter, Yvonne Pörs, Stephan Lorenzen, Bernhard Grimm and Olaf Czarnecki

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 5, pages 670-681
Published in print May 2010 | ISSN: 0032-0781
Published online April 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq047
Rapid Dark Repression of 5-Aminolevulinic Acid Synthesis in Green Barley Leaves

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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 d12 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.

Keywords: Acifluorfen; 5-Aminolevulinic acid; Chlorophyll; Dark repression; FLU; Heme; Protochlorophyllide; tigrina d12

Journal Article.  6687 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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