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The FRD3-Mediated Efflux of Citrate into the Root Vasculature Is Necessary for Efficient
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The results all strongly support the hypothesis that FRD3 effluxes citrate into the root vasculature, a process important for the translocation of iron to the leaves, as well as confirm previous reports suggesting that iron moves through the xylem as a ferric-citrate complex.Abstract:
Iron, despite being an essential micronutrient, becomes toxic if present at high levels. As a result, plants possess carefully regulated mechanisms to acquire iron from the soil. The ferric reductase defective3 (frd3) mutant of Arabidopsis (Arabidopsis thaliana) is chlorotic and exhibits constitutive expression of its iron uptake responses. Consequently, frd3 mutants overaccumulate iron; yet, paradoxically, the frd3 phenotypes are due to a reduction in the amount of iron present inside frd3 leaf cells. The FRD3 protein belongs to the multidrug and toxin efflux family, members of which are known to export low-M r organic molecules. We therefore hypothesized that FRD3 loads an iron chelator necessary for the correct distribution of iron throughout the plant into the xylem. One such potential chelator is citrate. Xylem exudate from frd3 plants contains significantly less citrate and iron than the exudate from wild-type plants. Additionally, supplementation of growth media with citrate rescues the frd3 phenotypes. The ectopic expression of FRD3-GFP results in enhanced tolerance to aluminum in Arabidopsis roots, a hallmark of organic acid exudation. Consistent with this result, approximately 3 times more citrate was detected in root exudate from plants ectopically expressing FRD3-GFP. Finally, heterologous studies in Xenopus laevis oocytes reveal that FRD3 mediates the transport of citrate. These results all strongly support the hypothesis that FRD3 effluxes citrate into the root vasculature, a process important for the translocation of iron to the leaves, as well as confirm previous reports suggesting that iron moves through the xylem as a ferric-citrate complex. Our results provide additional answers to longstanding questions about iron chelation in the vasculature and organic acid transport. Plants, like most other organisms, require iron for essential everyday processes. Iron’s usefulness is primarily derived from its ability to adopt two different ionic states; consequently, iron is present in many enzymes that catalyze redox reactions or are involved in electron transfer. Iron is abundant in most soils, yet exists mostly as Fe(III) hydroxides, which are sparingly soluble at neutral pH. Plants use two different strategies to extract iron under these conditions. One approach, called Strategy I and utilized by nongraminaceous species, involves the coordinate up-regulation of three biochemical activities in the roots of irondeficient plants (Marschner, 1995). The rhizosphere isread more
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Plant and microbial strategies to improve the phosphorus efficiency of agriculture
Alan Richardson,Alan Richardson,Jonathan P. Lynch,Peter R. Ryan,Emmanuel Delhaize,F. Andrew Smith,Sally E. Smith,Paul R. Harvey,Megan H. Ryan,Erik J. Veneklaas,Hans Lambers,Astrid Oberson,Richard A. Culvenor,Richard J. Simpson,Richard J. Simpson +14 more
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References
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Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana
Steven J. Clough,Andrew F. Bent +1 more
TL;DR: The modified method should facilitate high-throughput transformation of Arabidopsis for efforts such as T-DNA gene tagging, positional cloning, or attempts at targeted gene replacement.
Book
The Mineral Nutrition of Higher Plants
M. H. Martin,H. Marschner +1 more
TL;DR: This chapter discusses the relationship between Mineral Nutrition and Plant Diseases and Pests, and the Soil-Root Interface (Rhizosphere) in Relation to Mineral Nutrition.
Book
Mineral Nutrition of Higher Plants
TL;DR: In this article, the authors discuss the relationship between mineral nutrition and plant diseases and pests, and diagnose deficiency and toxicity of mineral nutrients in leaves and other aerial parts of a plant.
Journal ArticleDOI
Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents: verification of the concentration of chlorophyll standards by atomic absorption spectroscopy
TL;DR: In this paper, the extinction coefficients for chlorophylls a and b in diethylether (Smith, J.H. and Benitez, A.V., eds.), used in this paper as primary standards, were verified by magnesium determination using atomic absorbance spectrophotometry.
Journal ArticleDOI
IRT1, an Arabidopsis Transporter Essential for Iron Uptake from the Soil and for Plant Growth
Grégory Vert,Natasha Grotz,Fabienne Dédaldéchamp,Frédéric Gaymard,Mary Lou Guerinot,Jean-François Briat,Catherine Curie +6 more
TL;DR: Genetic evidence is presented that IRT1 is essential for the uptake of iron from the soil, and it is shown that I RT1 is expressed in the external cell layers of the root, specifically in response to iron starvation.