DIFFERENCES AND SIMILARITIES IN ROOTS OF THE NICKEL HYPERACCUMULATING AND NON-ACCUMULATING GENOTYPES

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P 36 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)

DIFFERENCES AND SIMILARITIES IN ROOTS OF THE NICKEL HYPERACCUMULATING AND NON-ACCUMULATING GENOTYPES

OF SENECIO CORONATUS FROM SOUTH AFRICA

J. Mesjasz-Przybylowicz^1∗, A. Barnabas¹, I. Yousef², P. Dumas², F. Jamme², Ch. Sandt², F. Guillon³, P. Sechogela¹, and W. Przybylowicz^1,4

1Materials Research Department, iThemba LABS, Somerset West 7129, South Africa

2Soleil Synchrotron BP 48 F91192 Gif sur Yvette Cedex, France

3UR1268 Biopolym´eres, Interactions, Assemblages INRA F–44316 Nantes, France

4on leave from the Faculty of Physics and Applied Computer Science, University of Science and Technology, Krakow, Poland

Keywords: synchrotron radiation, Senecio coronatus, Asteraceae, ultramafic soil, nickel hyperaccumulation, infrared microspectroscopy, X-ray microanalysis, root, cytology, chemotaxonomy

∗e-mail : mesjasz@tlabs.ac.za

Hyperaccumulation of heavy metals by a small number of certain plant species is a unique and fas- cinating phenomenon of great interest from a phys- iological point of view. The uptake mechanism is still not well understood, despite increasing number of investigations concentrating on different aspects of hyperaccumulation.

Senecio coronatus (Thunb.) Harv. Asteraceae (Hilliard 1977), is a very interesting example of a plant’s adaptation to different ecological conditions.

The species is widespread in grasslands in South Africa but is also found on ultramafic outcrops.

Populations of S. coronatus occurring on ultramafic soils differ in terms of Ni uptake and represent Ni-hyperaccumulating and non-hyperaccumulating genotypes. The aim of the present study was to investigate the cytology of the roots of both genotypes, their Ni content and tissue distribution, and to ascertain whether there was a cytological basis for the differential uptake of Ni.

Light and fuorescence microscopy together with histochemical methods and TEM were used to study root cytology. X-ray microanalysis by means of a nuclear microprobe [particle-induced X-ray emission (PIXE) and proton backscattering (BS) techniques]

was utilized to determine the concentration and distribution of Ni and other elements in freeze-dried root cross-sections (iThemba LABS, South Africa).

Synchrotron Infrared Microspectroscopy was used to get a deeper insight of biochemical differences between the nickel hyperacummulating and non-accumulating genotypes. The experiment was performed at the SOLEIL synchrotron facil- ity, France (Beam-line SMIS equipped with a Nic- plan IR microscope coupled to a Nicolet Magna 860 FT-IR spectrometer (Thermo Scientific, Nicolet- USA). Results were evaluated using statistical ap- proaches (Principal Component Analysis PCA).

Results from investigations on S. coronatus genotypes showed interesting cytological differences in the inner cortical region and exodermis of the

roots. Distinct groups of specialized cells with an organelle-rich cytoplasm that produced copious numbers of spherical bodies, occurred in the inner cortical region of the hyperaccumulator [1, 2].

Such distinct cell groups were absent from the inner cortex of the non-accumulator. Histochemical tests identified a mixture of lipids, alkaloids and ter- penoids within the specialized groups of cells. Cas- parian bands were identified in exodermal cell walls of both genotypes but the bands fuoresced more intensely in the non-accumulator suggesting differences in chemical composition and probably also in apoplastic barrier efficiency. Results from infrared microspectroscopy showed significant differences between the specialized cells as well as cortex and pith regions of the Ni-hyperaccumulator roots compared to the same regions of the non-accumulator.

Further studies of the apoplastic barriers, specialized cells and secreted material in roots of both populations of S. coronatus are continued in order to gain a better understanding of their functions.

Acknowledgments: The authors greatly acknowl- edge Mpumalanga Parks Boards, SAFCOL and SAPPI Forestry for permission to access sites and all assistance.

This work is based upon research supported by the South African National Research Foundation. Any opin- ion, finding, conclusion or recommendation expressed in this material are those of the authors and therefore the NRF does not accept any liability in regards thereto.

References

[1] J. Mesjasz-Przyby lowicz, A. Barnabas, W.J.

Przyby lowicz, “Comparison of cytology and distribution of nickel in roots of Ni-hyperaccumulating and non-accumulating genotypes of Senecio coronatus,” Plant and Soil 293 (2007) 61 – 78.

[2] J. Mesjasz-Przyby lowicz, A. Barnabas and W.

Przyby lowicz, “Root ultrastructure of Senecio coronatus genotypes differing in Ni uptake,”

Northeast. Nat. 16 (Special Issue 5) (2009) 351 – 365.

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