Alteration of citrate metabolism in cluster roots of white lupin [Lupinus albus]

• Published in: Plant and cell physiology Vol. 44; no. 9; pp. 901 - 908
• Main Authors: Kihara, T. (Gifu Univ. (Japan). Faculty of Agriculture), Wada, T, Suzuki, Y, Hara, T, Koyama, H
• Format: Journal Article
• Language: English
• Published: Japan Oxford University Press 01.09.2003; Oxford Publishing Limited (England)
• Subjects: Base Sequence; citrate synthase; CITRATES; Citrates - metabolism; DNA Primers; Enzymes - metabolism; EXCRETION; ICDH; ISOCITRATE DEHYDROGENASE; Keywords: Citrate excretion — Lupinus albus — NADP-specific isocitrate dehydrogenase — Pi-acquisition — phosphoenolpyruvate phosphatase; Lupinus - enzymology; Lupinus - metabolism; LUPINUS ALBUS; NADP-isocitrate dehydrogenase; PEP; PEPCase; phosphoenolpyruvate; phosphoenolpyruvate carboxylase; Phosphorus - metabolism; Plant Roots - enzymology; Plant Roots - metabolism; pyruvate kinase; reverse transcription-PCR; ROOTS; RT-PCR
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcg115

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 micromol (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.