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\hypersetup{pdftitle={Visualisation of Fe2+ Partitioning by Different Rice Genotypes under Conditions of Iron Toxicity},pdfauthor={Katrin Engel, Mathias Becker, Folkard Asch},pdfsubject={Tropentag 2010: Abstract},pdfkeywords={2,2 dipyridyl (DPD), iron toxicity, Oryza sativa  L., tissue tolerance},pdfpagemode=None,colorlinks=true}
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\begin{document}
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\parbox[b]{13.4cm}{\centering \large{\textbf{Tropentag, September 14-16, 2010, Zurich}}\\[1ex] \Large{``World Food System  ---\\A Contribution from Europe''\\[2ex]}}
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\Large{\textbf{Visualisation of Fe2+ Partitioning by Different Rice Genotypes under Conditions of Iron Toxicity\footnote{\textbf{Contact Address:} Mathias Becker, University of Bonn, Institute of Crop Science and Resource Conservation (INRES) - Plant Nutrition, Karlrobert-Kreiten-Str. 13, 53115~Bonn, Germany, \mbox{e-mail}: \email{mathias.becker@uni-bonn.de}}\\[0.8ex]}}
\normalsize{\textsc{Katrin Engel$^{1}$, Mathias Becker$^{2}$, Folkard Asch$^{3}$}}
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\begin{itemize*}
\item[]{\small{\textit{$^{1}$University of Bonn, Institute of Crop Science and Resource Conservation (INRES) - Plant Nutrition, Germany}}}
\item[]{\small{\textit{$^{2}$University of Bonn, Institute of Crop Science and Resource Conservation (INRES) - Plant Nutrition, Germany}}}
\item[]{\small{\textit{$^{3}$University of Hohenheim, Dept. of Plant Production and Agroecology in the Tropics and Subtropics, Germany}}}
\end{itemize*}
\index[author]{Engel, Katrin}
\index[author]{Becker, Mathias}
\index[author]{Asch, Folkard}
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\textbf{Abstract}
\begin{abstract}
\normalsize{
Iron toxicity is a wide"=spread abiotic stress in lowland rice. The uptake of toxic Fe2+ from the soil solution and its transport in the plant follow the transpiration stream to the leaves. High amounts of Fe2+ in the leaf symplast lead to irreversible damages due to the formation of radical oxygen species and become visible as bronzing symptoms. Tolerant genotypes can either avoid the uptake of Fe2+ by oxidation in the rhizosphere or tolerate elevated Fe2+ concentrations in the plant by immobilisation or detoxification. The determination of the mechanisms in the process of varietal screening usually involves the chemical tissue analysis and the use of radioactive isotopes, however without satisfactorily discriminating between the oxidised Fe3+ and toxic Fe2+. We propose a new method to visualise in"=vivo the uptake, translocation and partitioning of Fe2+ in rice plants that based on the selective formation of a red colour complex of Fe2+ with 2,2 dipyridyl (DPD). We compared six rice genotypes, differing in their Fe sensitivity and the involved tolerance mechanisms. After applying an iron pulse of 1500 ppm Fe2+ for 1--4 days, 40-day"=old hydroponically"=grown rice plants were transferred to a 5 mM DPD solution. The translocation and fate of Fe2+ were studied by microscopy observing the sites and the timing of occurrence of the red colour in different organs. The colour intensity was used as a semi"=quantitative measure of Fe2+ in the plant tissues. We observed large genotypic differences regarding the iron form (red Fe2+ vs. brown Fe3+), the concentration and its distribution in roots, xylem vessels, and the leaf apoplast. The excluder genotype Pokkali accumulated the oxidised Fe3+ either at the root surface or within the root aerenchyma. The tolerant includer ITA 306 showed deep red colouration of leaf veins and large deposition of Fe3+ in the leaf apoplast. Sensitive genotypes rapidly translocated Fe2+ into the leaves where intercostals areas rapidly turned brown as a result of phenol oxidation. This method allows the determination of the prevailing tolerance mechanism without the use of radioactive isotopes and is suggested be used in future screening work. 







}

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\noindent \textbf{Keywords:} 2,2 dipyridyl (DPD), iron toxicity, \textit{Oryza sativa}  L., tissue tolerance
\index[key]{2,2 dipyridyl (DPD)}
\index[key]{Iron!toxicity}
\index[key]{Oryza sativa@\textit{Oryza sativa}  L.}
\index[key]{Tissue tolerance}
\end{document}