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First published online March 16, 2007; 10.1104/pp.106.092130 Plant Physiology 144:232-247 (2007) © 2007 American Society of Plant Biologists OPEN ACCESS ARTICLE
Differential Effects of Sucrose and Auxin on Localized Phosphate Deficiency-Induced Modulation of Different Traits of Root System Architecture in Arabidopsis1,[C],[W],[OA]Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907–1165
Phosphorus, one of the essential elements for plants, is often a limiting nutrient in soils. Low phosphate (Pi) availability induces sugar-dependent systemic expression of genes and modulates the root system architecture (RSA). Here, we present the differential effects of sucrose (Suc) and auxin on the Pi deficiency responses of the primary and lateral roots of Arabidopsis (Arabidopsis thaliana). Inhibition of primary root growth and loss of meristematic activity were evident in seedlings grown under Pi deficiency with or without Suc. Although auxin supplementation also inhibited primary root growth, loss of meristematic activity was observed specifically under Pi deficiency with or without Suc. The results suggested that Suc and auxin do not influence the mechanism involved in localized Pi sensing that regulates growth of the primary root and therefore delineates it from sugar-dependent systemic Pi starvation responses. However, the interaction between Pi and Suc was evident on the development of the lateral roots and root hairs in the seedlings grown under varying levels of Pi and Suc. Although the Pi+ Suc– condition suppressed lateral root development, induction of few laterals under the Pi– Suc– condition point to increased sensitivity of the roots to auxin during Pi deprivation. This was supported by expression analyses of DR5::uidA, root basipetal transport assay of auxin, and RSA of the pgp19 mutant exhibiting reduced auxin transport. A significant increase in the number of lateral roots under the Pi– Suc– condition in the chalcone synthase mutant (tt4-2) indicated a potential role for flavonoids in auxin-mediated Pi deficiency-induced modulation of RSA. The study thus demonstrated differential roles of Suc and auxin in the developmental responses of ontogenetically distinct root traits during Pi deprivation. In addition, lack of cross talk between local and systemic Pi sensing as revealed by the seedlings grown under either the Pi– Suc– condition or in the heterogenous Pi environment highlighted the coexistence of Suc-independent and Suc-dependent regulatory mechanisms that constitute Pi starvation responses.
1 This work was supported by the U.S. Department of Agriculture and McKnight grants (to K.G.R.) and the U.S. Department of Agriculture-National Research Initiative (grant to A.S.M.). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Kashchandra G. Raghothama (kragu{at}purdue.edu). [C] Some figures in this article are displayed in color online but in black and white in print. [W] The online version of this article contains Web-only data. [OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.106.092130 * Corresponding author; e-mail kragu{at}purdue.edu; fax 765–494–0391. Received October 27, 2006; accepted March 10, 2007; published March 16, 2007. This article has been cited by other articles:
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