Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2010
Publication Date: 9/1/2010
Publication URL: http://hdl.handle.net/10113/47016
Citation: Wang, B.L., Tang, X.Y., Cheng, L.Y., Zhang, A.Z., Zhang, W.H., Zhang, F.S., Liu, J.Q., Cao, Y., Allan, D.L., Vance, C.P., Shen, J.B. 2010. Nitric oxide is involved in phosphorus deficiency-induced cluster-root development and citrate exudation in white lupin. New Phytologist. 187(4):1112-1123. Interpretive Summary: The use of phosphorus (P) fertilizer in agriculture is a "two-edged sword." Too much P fertilizer added to a crop can result in water pollution, while too little P fertilizer will result in poor crop growth. Understanding how plants acquire and use P fertilizer may lead to more efficient P-fertilizer utilization. White lupin plants when grown under low P fertilizer show many adaptations to more efficiently acquire P including: unusually clustered lateral roots, release of enzymes that solubilize P, and exudation of organic acids to release bound P. In this study we evaluated whether the signal molecule nitric oxide played a role in the formation of white lupin clustered lateral roots during P-deficiency. Plants were treated with compounds that either increase nitric oxide release or reduce nitric oxide synthesis. The results showed that clustered lateral roots produce more nitric oxide than normal roots. Treatments that increase nitric oxide synthesis also increased clustered lateral roots. Inhibition of nitric oxide synthesis resulted in reduced clustered lateral root formation and exudation of organic acids. Inhibition of xanthine oxidase, an enzyme involved in nitric oxide synthesis, blocked the formation of nitric oxide and resulted in altered cluster roots. These data are useful because they show that the signal molecule nitric oxide is involved in clustered lateral root formation as white lupin acclimates to low P fertilizer. Manipulation of nitric oxide may improve the utilization of P fertilizer.
Technical Abstract: White lupin (Lupinus albus) forms specialized cluster roots characterized by exudation of organic anions under phosphorus (P) deficiency. Here, we evaluated the role of nitric oxide (NO) in P deficiency-induced cluster-root formation and citrate exudation in white lupin. Plants were treated with NO donor sodium nitroprusside (SNP), scavenger and inhibitor of NO synthase under P deficiency or sufficiency. Phosphorus deficiency enhanced NO production in primary and lateral root-tips, with greater NO levels in cluster roots than in non-cluster roots. The NO levels decreased with cluster-root development from pre-emergent, juvenile, to mature stages. Pharmacological studies revealed that increased NO levels in P-deficient roots were related to NO synthase- and xanthine oxidoreductase-mediated NO synthesis pathways. Treatment with SNP markedly increased the number of cluster roots in white lupin. Citrate exudation from different root segments was positively correlated with endogenous NO levels in roots. These findings demonstrate differential patterns of NO production in white lupin, depending on root-zones, developmental stages, and P-nutritional status. NO is involved in P deficiency-induced cluster-root formation and citrate exudation.