Tomasi Nicola, Kretzschmar Tobias, Espen Luca, Weisskopf Laure, Fuglsang Anja Thoe, Palmgren Michael Gjedde, Neumann Günter, Varanini Zeno, Pinton Roberto, Martinoia Enrico, Cesco Stefano
Dipartimento di Scienze Agrarie e Ambientali, University of Udine, Via delle Scienze 208, I-33100 Udine, Italy.
Plant Cell Environ. 2009 May;32(5):465-75. doi: 10.1111/j.1365-3040.2009.01938.x. Epub 2009 Jan 14.
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.
白羽扇豆（Lupinus albus L.）能够通过产生一种叫做簇生根的特殊结构，在有效磷含量低的土壤中生长。为了活化土壤中难溶性的磷形态，簇生根会释放大量的羧酸盐，并随之酸化根际环境。酸化作用与羧酸盐分泌之间的关系在很大程度上仍不为人所知。在本研究中，我们研究了缺磷白羽扇豆簇生根中有机酸（苹果酸和柠檬酸）与质子分泌之间的联系。光照开始后，柠檬酸分泌量短暂增加，并在5小时后达到最大值。体内核磁共振（NMR）分析表明，这种效应伴随着外部介质的强烈酸化和细胞质的碱化。壳梭孢菌素是一种质膜（PM）H⁺-ATP酶的激活剂，它能刺激柠檬酸分泌，而钒酸盐是H⁺-ATP酶的抑制剂，它能减少柠檬酸分泌。柠檬酸分泌的爆发与LHA1质膜H⁺-ATP酶基因表达的增加、H⁺-ATP酶蛋白量的增加、该酶最适pH值的变化以及涉及激活14-3-3蛋白结合的H⁺-ATP酶蛋白翻译后修饰有关。综上所述，我们的结果表明，缺磷白羽扇豆的簇生根中，柠檬酸分泌的爆发与质膜H⁺-ATP酶催化的质子外流之间存在密切联系。
