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Root tip-dependent, active riboflavin secretion by Hyoscyamus albus hairy roots under iron deficiency


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Title: Root tip-dependent, active riboflavin secretion by Hyoscyamus albus hairy roots under iron deficiency
Authors: Higa, Ataru / Miyamoto, Erika / Rahman, Laiq ur / Kitamura, Yoshie
Issue Date: 4-Apr-2008
Publisher: Elsevier Masson SAS.
Citation: Plant Physiology and Biochemistry 46(4), 452-460;2008
Abstract: Hyoscyamus albus hairy roots with/without an exogenous gene (11 clones) were established by inoculation of Agrobacterium rhizogenes. All clones cultured under iron deficient condition secreted riboflavin from root tips into the culture medium and the productivity depended on the number and size of root tips among the clones, although the addition of sucrose was essential for riboflavin production. A decline of pH was observed before riboflavin production and root development using either a root tip or propagated roots: propagated roots were employed for further work due to their lesser variation. Additions of proton-pump inhibitors, N,N’-dicyclohexylcarbodiimide (DCCD) at 100 and 10 μM and erythrosine B at 100 μM, suppressed the pH decline at 100 and 10 μM accompanied by inhibition of riboflavin secretion and root growth; at 10 μM of erythrosine B, pH decline occurred with a moderate delay, but both growth and riboflavin efflux were inhibited. Neither inhibition of the pH decline nor riboflavin production was observed at 1 μM. To examine the necessity of acidification and riboflavin secretion by the roots themselves, artificial pH reduction of culture medium with organic acids and the addition of exogenous riboflavin with/without pH reduction were performed. When hairy roots were cultured in iron-deficient medium acidified with citric acid (pH 4.0) or malic acid (pH 3.7), pH increased rapidly to around 5 overnight, following which riboflavin production and root growth occurred. Addition of riboflavin did not affect riboflavin secretion by the roots, but acidification with citric acid (pH 4.0) helped achiever greater riboflavin production and earlier pH elevation. These results indicate that riboflavin efflux does not directly connected to active pH reduction, and more significantly active riboflavin secretion occurs by internal requirement in H. albus hairy roots under iron deficiency.
Keywords: Hyoscyamus albus / hairy roots / iron deficiency / riboflavin / citric acid / malic acid / proton-pump inhibitor / Abbreviations / DCCD, N,N’-dicyclohexylcarbodiimide / FAD, flavinadenindinucleotide / FMN, flavinmononucleotide / H6H, hyoscyamine 6β-hydroxylase / HPLC, high-performance liquid chromatography / MS, Murashige and Skoog.
URI: http://hdl.handle.net/10069/16871
ISSN: 09819428
DOI: 10.1016/j.plaphy.2008.01.004
PubMed ID: 18367404
Rights: Copyright (c) 2008 Elsevier Masson SAS. All rights
Type: Journal Article
Text Version: author
Appears in Collections:Articles in academic journal

Citable URI : http://hdl.handle.net/10069/16871

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