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ENVIRONMENTAL STRESS AND ADAPTATION

Phosphatase Under-Producer Mutants Have Altered Phosphorus Relations¹

Intercollege Program in Plant Physiology (J.L.T., J.D., J.P.L., M.J.G.), Department of Biology (M.C.T., J.D., M.J.G.), and Department of Horticulture (J.P.L., M.J.G.), Penn State University, University Park, Pennsylvania 16802

Phosphorus (P) acquisition and partitioning are essential for plant homeostasis. P is available for plant uptake when in its inorganic form (H₂PO₄^–, or P_i), but P_i is often limiting in soils. Plants secrete acid phosphatases (APases) into the apoplastic space, which may be important for obtaining P_i from organic P sources; however, the relative importance of these enzymes for plant P nutrition has yet to be determined. We demonstrate that the root-associated APase pool is increased in Arabidopsis when P_i is limiting and document five APase isoforms secreted from Arabidopsis roots. Previously, we presented the identification of the phosphatase under-producer (pup) mutants, which have decreased in vivo root APase staining when grown under low P conditions. Here, we present the characterization of one of these, pup3, and further studies with pup1. pup3 has 49%, 38%, and 37% less specific APase activity in exudates, roots, and shoots, respectively. Root-associated APase activity is decreased by 16% in pup1 and 25% in pup3, regardless of P treatment. Two APase activity isoforms are reduced in pup3 exudates, and root and shoot isoforms are also affected. One of the two exudate isoforms is recognized by a polyclonal antibody raised to an Arabidopsis purple APase recombinant protein (AtPAP12); however, AtPAP12 transcript levels are unaffected in the mutant. The pup3 mutation was mapped to 68.4 ± 6.0 centimorgans on chromosome 5. Although P concentrations were not altered in pup1 and pup3 tissues when grown in nutrient solution in which P_i was the sole source of P, the mutants had 10% (pup1) and 17% (pup3) lower shoot P concentrations when grown in a peat-vermiculite mix in which the majority of the total P was present as organic P. Therefore, the pup defects, which include secreted APases, are functionally important for plant P nutrition.

² Present address: Biology Department, CB 3280, University of North Carolina, Chapel Hill, NC 27599.

³ Present address: Monsanto Company, 1920 Fifth Street, Davis, CA 95616.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.036459.

^* Corresponding author; e-mail tomscha{at}email.unc.edu; fax 919–962–1625.

Received November 20, 2003; returned for revision February 25, 2004; accepted March 7, 2004.

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