Journal Article

Alteration of Citrate Metabolism in Cluster Roots of White Lupin

Tomonori Kihara, Tatsumi Wada, Yuji Suzuki, Tetsuo Hara and Hiroyuki Koyama

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 9, pages 901-908
Published in print September 2003 | ISSN: 0032-0781
Published online September 2003 | e-ISSN: 1471-9053 | DOI: https://dx.doi.org/10.1093/pcp/pcg115
Alteration of Citrate Metabolism in Cluster Roots of White Lupin

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Organic acid excretion plays a key role in the superior Pi-acquisition of barely soluble inorganic P sources from soils. Seedlings of white lupin (Lupinus albus L.) grown for 37 d in –P nutrient solution showed typical –P symptoms, such as low P content, increased root/shoot ratio and the development of cluster roots which released large amounts of citrate. Citrate concentration in the cluster roots was 21.5 µmol (g FW)–1, which corresponded to a 4.3- and 2.6-fold increase of +P and –P root apexes, respectively. Cluster roots possessed higher phosphoenolpyruvate carboxylase and phosphoenolpyruvate phosphatase activity than those in +P root apexes, which could result in increasing the supply of substrate for citrate synthase. On the other hand, the cytosolic pathway which converts citrate to 2-oxoglutarate consists of aconitase and NADP-specific isocitrate dehydrogenase activity that was lower in the cluster roots than in +P root apexes, and may contribute to citrate accumulation. Thus, metabolic balance with these alterations would play an important role in increasing citrate concentration in the cluster roots. The molecular characterization of NADP-specific isocitrate dehydrogenase indicated that the cytosolic isoenzyme functions as a hetero-dimer, and that the activity would be regulated by the transcript levels for both isoforms.

Keywords: Keywords: Citrate excretion — Lupinus albus — NADP-specific isocitrate dehydrogenase — Pi-acquisition — phosphoenolpyruvate phosphatase.; Abbreviations: CS, citrate synthase; ICDH, NADP-isocitrate dehydrogenase; PEP, phosphoenolpyruvate; PEPCase, phosphoenolpyruvate carboxylase; PK, pyruvate kinase; RT-PCR, reverse transcription-PCR.

Journal Article.  6014 words.  Illustrated.

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

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