Plasma membrane H-ATPase-dependent citrate exudation from cluster roots of phosphate-deficient white lupin.
White lupin (Lupinus albus L.) is able to grow on soils with sparingly available phosphate (P) by producing specialized structures called cluster roots. To mobilize sparingly soluble P forms in soils, cluster roots release substantial amounts of carboxylates and concomitantly acidify the rhizosphere. The relationship between acidification and carboxylate exudation is still largely unknown. In the present work, we studied the linkage between organic acids (malate and citrate) and proton exudations in cluster roots of P-deficient white lupin. After the illumination started, citrate exudation increased transiently and reached a maximum after 5 h. This effect was accompanied by a strong acidification of the external medium and alkalinization of the cytosol, as evidenced by in vivo nuclear magnetic resonance (NMR) analysis. Fusicoccin, an activator of the plasma membrane (PM) H+-ATPase, stimulated citrate exudation, whereas vanadate, an inhibitor of the H+-ATPase, reduced citrate exudation. The burst of citrate exudation was associated with an increase in expression of the LHA1 PM H+-ATPase gene, an increased amount of H+-ATPase protein, a shift in pH optimum of the enzyme and post-translational modification of an H+-ATPase protein involving binding of activating 14-3-3 protein. Taken together, our results indicate a close link in cluster roots of P-deficient white lupin between the burst of citrate exudation and PM H+-ATPase-catalysed proton efflux.
Tomasi
Nicola
N
Dipartimento di Scienze Agrarie e Ambientali, University of Udine, Via delle Scienze 208, I-33100 Udine, Italy. nicola.tomasi@uniud.it
Kretzschmar
Tobias
T
Espen
Luca
L
Weisskopf
Laure
L
Fuglsang
Anja Thoe
AT
Palmgren
Michael Gjedde
MG
Neumann
Günter
G
Varanini
Zeno
Z
Pinton
Roberto
R
Martinoia
Enrico
E
Cesco
Stefano
S
D019343:Citric Acid / Q000378:metabolism*; D004338:Drug Combinations; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D006027:Glycosides / Q000494:pharmacology; D031297:Lupinus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D009821:Oils; D010636:Phenols; D010710:Phosphates / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
D004338:Drug Combinations; D006027:Glycosides; D008293:Malates; D009821:Oils; C027222:P & S Liquid; D010636:Phenols; D010710:Phosphates; D010940:Plant Proteins; C007808:fusicoccin; D019343:Citric Acid; D014638:Vanadates; C030298:malic acid; D006180:Proton-Translocating ATPases