Scheuermann, Enrico B. :
ISBN 9783899598933

Speciation and physiological characterization of metal ligands and their complexes with iron and other heavy metals in plants # Pb., 156 S., 34 Abb., davon 4 in Farbe, 4 Tab.


SCHLAGWORTE:
Plant nutrition
Plant physiology
Micronutrients
Pflanzenernährung
Pflanzenphysiologie

Despite its key function in redox reactions and its harmful oxidative potential in plant cells, neither long-distance transport nor intracellular trafficking of Fe have been intensively investigated. Especially for Strategy II plants which encompass important crop species that considerably contribute to Fe nutrition in humans, the knowledge on Fe distribution within the plant is poor. Moreover, there is an urgent need to develop crops with elevated Fe levels, particularly the harvested products, since Fe deficiency is the most common and widespread nutritional disorder in the world.
In spite of the improved techniques for the analysis of metal species in plants, only a few attempts have been made to analyze intact metal complexes in plant samples. Therefore, the primary aim of present thesis focused on the understanding of complex formation and, in more detail, on metal interactions with plant-borne chelators.
Previous methods for PS determination were mainly based on HPLC with post-column derivatization and fluorescence detection (Kawai et al., 1987; Mori et al., 1987; Neumann et al., 1999) or pulsed amperometric detection (Weber et al., 2001). Both methods are well suited for the detection of PS in the low micromolar range, but not capable for the detection of intact metal species. Thus, the first part of this thesis focused on the development of MS-based analytical methods allowing the separation and identification of different PS, NA, and their corresponding metal complexes with Fe, Cu, Zn, and Ni. Due to the fact that PS chelate other divalent metal cations besides Fe(II) and Fe(III), a hypothesis has been raised by Hill et al. (2002), in which exposure of roots to toxic Cd

concentrations might induce the release of PS allowing external sequestration of Cd2+ and thus lower uptake into roots. Since this study only provided indirect evidence for Cd interactions with Fe and Fe nutrition in maize, chapter 3 revisited this topic by a combination of physico-chemical and molecular biological approaches. In the next chapter, the question was addressed why plants produce several PS species that differ only in their degree of hydroxylation. The major aim here was to investigate the role of one or two additional hydroxyl groups in the PS backbone with regard to their efficiency in Fe acquisition. Therefore, the three PS species DMA, MA, and epiHMA were guided through a set of experiments that reflected the separate processes of Fe(III) mobilization, Fe(III) chelation efficiency, Fe(III)-PS uptake and the delivery of Fe(III) from the PS- to a NA-chelate, as this latter process is expected to occur in the cytoplasm of root cells.
Finally, the results from the above-mentioned chapters are discussed in a broader context, with particular focus on the importance of the physico-chemical properties of Fe-PS chelates for their physiological function.

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