Metabolic changes associated with cluster root development in white lupin (Lupinus albus L.): relationship between organic acid excretion, sucrose metabolism and energy status

• Published in: Planta 2001-08, Vol.213 (4), p.534-542
• Main Authors: Massonneau, Agnès, Langlade, Nicolas, Léon, Sébastien, Smutny, Jana, Vogt, Esther, Neumann, Günter, Martinoia, Enrico
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Agronomy. Soil science and plant productions; Alcohol Dehydrogenase - metabolism; Biological and medical sciences; Citrates; Citric Acid - metabolism; Economic plant physiology; Enzymes; Ethanol; Excretion; Fabaceae - genetics; Fabaceae - growth & development; Fabaceae - metabolism; Fructokinases - genetics; Fructokinases - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Glucosyltransferases - genetics; Glucosyltransferases - metabolism; Hydrogen-Ion Concentration; Life Sciences; Malates - metabolism; Metabolism; Net assimilation, photosynthesis, carbon metabolism. Photorespiration, respiration, fermentation (anoxia, hypoxia); Nutrition. Photosynthesis. Respiration. Metabolism; Organic acids; Oxygen Consumption; Phosphates; Phosphates - metabolism; Phosphoglucomutase - genetics; Phosphoglucomutase - metabolism; Phosphorus; Photosynthesis, respiration. Anabolism, catabolism; Plant physiology and development; Plant Proteins - metabolism; Plant roots; Plant Roots - genetics; Plant Roots - growth & development; Plant Roots - metabolism; Plants; Pyruvate Decarboxylase - metabolism; RNA; RNA, Plant - analysis; Vegetal Biology
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s004250100529

Under phosphorous deficiency, plants of white lupin (Lupinus albus L.) develop root clusters, which are also called proteoid roots due to their preferential presence in the Proteaceae. In their mature stage, these roots acidify the soil and excrete high amounts of carboxylates [up to 1.5 and 7 μmol (g FW)-1 h-1 of malate and citrate, respectively] enabling lupins to utilise sparingly available sources of phosphate. Using the amplified fragment length polymorphism (AFLP) technique, we identified genes predominantly expressed in juvenile and mature cluster roots. Transcripts for two enzymes involved in glycolysis, fructokinase and phosphoglucomutase, were identified in juvenile cluster roots and one, sucrose synthase, in mature cluster roots. In order to verify these observations we performed quantitative reverse transcription-polymerase chain reaction (RT-PCR) and could confirm the increased transcript level. Measurements of enzymatic activities showed that fructokinase and phosphoglucomutase activities increased in juvenile cluster roots, whereas sucrose synthase activity was maximal in mature cluster roots. These results indicate that formation of proteoid roots and citrate excretion increase sink strength locally. Production of citrate and inhibition of respiration are likely to result in an increased NADH/NAD+ ratio, which may be toxic for the plant. The fermentation pathway would allow oxidation of NADH by decarboxylation of pyruvate and subsequent reduction of the resulting acetaldehyde. Determination of alcohol dehydrogenase activity showed that this enzyme is strongly induced in mature proteoid roots. However, ethanol production was not increased, indicating that pyruvate is shunted to citrate synthesis and not to ethanol production.