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, Co2+) on P concentrations in roots and shoots of Medicago falcata seedlings grown in P-sufficient (500 mu M H2PO4-) and P-deficient (5 mu M H2PO4-) 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 concentration was reversed by AVG and Co2+, 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 Co2+. 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 Co2+. 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 phosphorus was added to the P-deficient solution, and the increase in P concentration was significantly inhibited by AVG and Co2+. These results indicate that ethylene plays an important role in modulation of P acquisition by possibly mobilizing organic P via up-regulating root APase activity and high-affinity phosphate transporters. (C) 2010 Elsevier B.V. All rights reserved.