Environmental and Experimental Botany 71 (2011) 114–120 Contents lists available at ScienceDirect Environmental and Experimental Botany journal homepage: www.elsevier.com/locate/envexpbot Stimulation of root acid phosphatase by phosphorus deficiency is regulated by ethylene in Medicago falcata Yan-Su Li a , Yan Gao a,b , Qiu-Ying Tian a , Feng-Ling Shi b,∗∗ , Ling-Hao Li a , Wen-Hao Zhang a,∗ a State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, PR China b College of Ecology and Environmental Science, Inner Mongolia Agricultural University, Huhehot 010018, PR China article info Article history: Received 1 July 2010 Received in revised form 9 November 2010 Accepted 14 November 2010 Keywords: Phosphorus deficiency Ethylene Medicago falcata Acid phosphatase activity Phosphate transporters Organic phosphorus abstract Plants have developed numerous strategies to cope with phosphorus (P) deficiency resulting from low availability in soils. Evolution of ethylene and up-regulation of root secreted acid phosphatase activity are common for plants in response to P deficiency. To determine the role of ethylene in response of plants to P deficiency, we investigated the effects of ethylene precursor (1-amino cyclopropane-1-carboxylic acid, ACC) and ethylene synthesis antagonists (aminoethoxyvinylglycine AVG, cobalt, Co 2+ ) on P con- centrations in roots and shoots of Medicago falcata seedlings grown in P-sufficient (500 MH 2 PO 4 - ) and P-deficient (5 MH 2 PO 4 - ) solution. After transferring M. falcata seedlings from P-sufficient to P-deficient solution for 2 days, root P concentration was significantly reduced. The reduction in root P concentra- tion was reversed by AVG and Co 2+ , and a similar reduction in root P concentration of seedlings exposed to P-sufficient solution was observed by ACC. Expression of high-affinity phosphate transporters (MfPT1, MfPT5) was enhanced by P-deficiency and this process was reversed by AVG and Co 2+ . There was a marked increase in activity of root acid phosphatase (APase) and expression of gene encoding APase (MfPAP1) under P-deficient conditions, and the increase in APAse activity and expression of MfPAP1 was inhibited by AVG and Co 2+ . APase activity and expression of MfPAP1 expression in seedlings grown in P-sufficient solution were enhanced by ACC. Root and shoot P concentrations were increased when organic phospho- rus was added to the P-deficient solution, and the increase in P concentration was significantly inhibited by AVG and Co 2+ . These results indicate that ethylene plays an important role in modulation of P acqui- sition by possibly mobilizing organic P via up-regulating root APase activity and high-affinity phosphate transporters. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Phosphorus (P) is a critical macronutrient required for numer- ous functions in plants and is one of the limiting factors for plant growth due to its rapid immobilization by soil organic and inor- ganic components (for review, see Vance et al., 2003; Richardson et al., 2009). The application of P fertilizer to cropland has become a routine agricultural practice worldwide. However, the use of P fertilizer is not only expensive but is also polluting environment and non-sustainable. Thus, it is imperative to elucidate the mecha- nisms by which plants respond and adapt to the P-deficient growth medium. ∗ Corresponding author at: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, PR China. Tel.: +86 10 6283 6697l; fax: +86 10 6259 2430. ∗∗ Corresponding author. Tel.: +86 471 4301371; fax: +86 471 4300732. E-mail addresses: sfl0000@126.com (F.-L. Shi), whzhang@ibcas.ac.cn (W.-H. Zhang). Plants have evolved numerous mechanisms to adapt to P- deficient soils. These include changes in root architecture to maximize surface area for uptake of P with the extreme exam- ple being the development of specialized “cluster root” in certain species (Shane and Lambers, 2005), acidification of root rhizo- sphere and exudation of organic anions to solubilize P that is bound with cations and other mineral ligands in the soil (Ryan et al., 2001), and secretion and expression of acid phosphatases from roots to hydrolyze soil organic P (George et al., 2005; Tran et al., 2010). In soils, up to 80% of total P occurs as organic P that comprises mainly monoesters (Richardson et al., 2009). Although the overall significance of soil organic P in plant nutrition remains unknown, it has been shown that plants can use several P sources in both sand and soil culture (Duff et al., 1994; Li et al., 2003). Soil organic P has to be hydrolyzed to inorganic P that is available to plants by phosphatases prior to acquisition by plants. Acid phosphatases (APase, EC 3.1.3.2) catalyze the hydrolysis of P from a broad and overlapping range of P-monoesters with an acidic pH optimum (Duff et al., 1994). A number of studies have reported that secretion and expression of APase are enhanced under P-deficient conditions 0098-8472/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2010.11.007