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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

An Improved Grafting Technique for Mature Arabidopsis Plants Demonstrates Long-Distance Shoot-to-Root Transport of Phytochelatins in Arabidopsis^1,[W]

Division of Biological Sciences, Cell and Developmental Biology Section, and Center for Molecular Genetics (A.C., J.I.S.), and Department of Chemistry and Biochemistry (E.A.K.), University of California, San Diego, La Jolla, California 92093–0116

Phytochelatins (PCs) are peptides that function in heavy-metal chelation and detoxification in plants and fungi. A recent study showed that PCs have the ability to undergo long-distance transport in a root-to-shoot direction in transgenic Arabidopsis (Arabidopsis thaliana). To determine whether long-distance transport of PCs can occur in the opposite direction, from shoots to roots, the wheat (Triticum aestivum) PC synthase (TaPCS1) gene was expressed under the control of a shoot-specific promoter (CAB2) in an Arabidopsis PC-deficient mutant, cad1-3 (CAB2::TaPCS1/cad1-3). Analyses demonstrated that TaPCS1 is expressed only in shoots and that CAB2::TaPCS1/cad1-3 lines complement the cadmium (Cd) and arsenic metal sensitivity of cad1-3 shoots. CAB2::TaPCS1/cad1-3 plants exhibited higher Cd accumulation in roots and lower Cd accumulation in shoots compared to wild type. Fluorescence HPLC coupled to mass spectrometry analyses directly detected PC2 in the roots of CAB2:TaPCS1/cad1-3 but not in cad1-3 controls, suggesting that PC2 is transported over long distances in the shoot-to-root direction. In addition, wild-type shoot tissues were grafted onto PC synthase cad1-3 atpcs2-1 double loss-of-function mutant root tissues. An Arabidopsis grafting technique for mature plants was modified to obtain an 84% success rate, significantly greater than a previous rate of approximately 11%. Fluorescence HPLC-mass spectrometry showed the presence of PC2, PC3, and PC4 in the root tissue of grafts between wild-type shoots and cad1-3 atpcs2-1 double-mutant roots, demonstrating that PCs are transported over long distances from shoots to roots in Arabidopsis.

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: Julian I. Schroeder (julian{at}biomail.ucsd.edu).

^[W] The online version of this article contains Web-only data.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.072637.

^* Corresponding author; e-mail julian{at}biomail.ucsd.edu; fax 858–534–7108.

Received October 11, 2005; returned for revision February 19, 2006; accepted February 21, 2006.

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