Structural and Ultrastructural Changes in Heavy Metal Exposed Plants
Visible symptoms of metal toxicity stress in plants are an expression of preceding metalinduced alterations at the structural and ultrastructural level. These changes at the cell, tissue, and organ level, in turn, are either the result of a direct interac
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Structural and Ultrastructural Changes in Heavy Metal Exposed Plants
J. Barce16, Ch. Poschenrieder
Laboratorio de Fisiologia Vegetal, Facultad de Ciencias, Universidad Aut6noma de Barcelona, 08193 Bellaterra, Spain
9.1
INTRODUCTION
Visible symptoms of metal toxicity stress in plants are an expression of preceding metalinduced alterations at the structural and ultrastructural level. These changes at the cell, tissue, and organ level, in turn, are either the result of a direct interaction of the toxic metals with structural components at these sites or a more indirect consequence of changes in signal transduction and/ or metabolism. Investigations at the structural and ultrastructurallevel help to identify the sites of the primary toxicity effects and their consequences for whole plant performance. Electron microscopy (EM), especially when combined with analytical techniques such as energy dispersive X-ray micro analysis (EDXA), laser microprobe mass analysis (LAMMA), electron energy loss spectroscopy (EELS; Lichtenberger and Neumann 1997), secondary ion mass spectrometry (SIMS), or cytochemical methods, are powerful tools yielding valuable information for further experiments on primary mechanisms of metal toxicity and tolerance at the molecular level. The recent development of atomic force microscopy allowing imaging of living cells and, especially, the fast introduction of laser scanning optical microscopy using confocal microscopy or multi-photon excitation in combination with the development of more powerful and user-friendly image analysis programs are also providing new possibilities for investigations into heavy metal effects at the cell and tissue level. It is not the aim of this chapter to exhaustively describe heavy metal effects at the structural and ultrastructural level, but to consider mainly those cases where the structural and ultrastructural approach is contributing to a better understanding of metal toxicity and tolerance mechanisms in plants. In this context, Al will also be included. Aluminum, although not being a "heavy" metal, is one of the major causes for inhibition of plant growth on acid soils in the tropics (Foy 1984). Research on Al provides
M. N. V. Prasad (ed.), Heavy Metal Stress in Plants © Springer-Verlag Berlin Heidelberg 2004
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a clear example for the usefulness of structural and ultrastructural investigations for the recognition of primary sites of injury, and the establishment of mechanisms of metal ion toxicity and tolerance. Although this chapter mainly concerns terrestrial higher plants, aquatic micro- and macrophytes deserve special mention, because of both the importance of these organisms in water pollution monitoring and control, and the numberous investigations at the ultrastructural level performed in these species.
9.2
STRUCTURAL AND ULTRASTRUCTURAL EFFECTS IN ALGAE
The structural simplicity of algae, in comparison with higher vascular plants, is very attractive for i
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