title: A re-assessment of sucrose signaling involved in cluster-root formation and function in phosphate-deficient white lupin (Lupinus albus).
abstract: Apart from substrate functions, a signaling role of sucrose in root growth regulation is well established. This raised the question whether sucrose signals might also be involved in formation of cluster-roots (CRs) under phosphate (Pi) limitation, mediating exudation of phosphorus (P)-mobilizing root exudates, e.g. in Lupinus albus and members of the Proteaceae. Earlier studies demonstrated that CR formation in L. albus was mimicked to some extent by external application of high sucrose concentrations (25 mM) in the presence of extremely high P supply (1-10 mM), usually suppressing CR formation. In this study, we re-addressed this question using an axenic hydroponic culture system with normal P supply (0.1 mM) and a range of sucrose applications (0.25-25 mM). The 2.5 mM sucrose concentration was comparable with internal sucrose levels in the zone of CR initiation in first-order laterals of P-deficient plants (3.4 mM) and induced the same CR morphology. Similar to earlier studies, high sucrose concentrations (25 mM) resulted in root thickening and inhibition of root elongation, associated with a 10-fold increase of the internal sucrose level. The sucrose analog palatinose and a combination of glucose/fructose failed to stimulate CR formation under P-sufficient conditions, demonstrating a signal function of sucrose and excluding osmotic or carbon source effects. In contrast to earlier findings, sucrose was able to induce CR formation but had no effect on CR functioning with respect to citrate exudation, in vitro activity and expression of genes encoding phosphoenolpyruvate carboxylase, secretory acid phosphatase and MATE transporters, mediating P-mobilizing functions of CRs.
authors.affiliation: Nutritional Crop Physiology (340h), Institute of Crop Science, University of Hohenheim, Stuttgart, 70593, Germany.
authors.forename: Zhengrui
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Plant Nutrition, China Agricultural University, Key Laboratory of Plant-Soil Interactions, Beijing, 100193, China.
authors.forename: Jianbo
authors.initials: J
authors.lastname: Shen
authors.affiliation: Nutritional Crop Physiology (340h), Institute of Crop Science, University of Hohenheim, Stuttgart, 70593, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Ludewig
authors.affiliation: Nutritional Crop Physiology (340h), Institute of Crop Science, University of Hohenheim, Stuttgart, 70593, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Neumann
mesh_terms: D000135:Acid Phosphatase / Q000235:genetics / Q000378:metabolism; D002951:Citrates / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D018527:Hydroponics / Q000379:methods; D031297:Lupinus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism* / Q000494:pharmacology; D010730:Phosphoenolpyruvate Carboxylase / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013395:Sucrose / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002951:Citrates; D010710:Phosphates; D010940:Plant Proteins; D013395:Sucrose; D000135:Acid Phosphatase; D010730:Phosphoenolpyruvate Carboxylase