Determination of Zn Distribution inside Edible Plants Grown on a by fdh56iuoui

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									     Determination of Zn Distribution inside Edible Plants Grown on
            a Polluted Soil Amended with Compost by XRF
                           Microtomography
                         1              1                2               2              1                   1
            R. Terzano , Z. Al Chami , B. Vekemans , K. Janssens ,T.M. Miano , and P. Ruggiero
1
    Dip. di Biologia e Chimica Agroforestale ed Ambientale, University of Bari, Via Amendola 165/A, I-70126 Bari, Italy
             2
               Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium

    High amounts of heavy metals in soil may cause toxicity effects in cultivated plants as well as pose
    a serious risk for human health, especially when these vegetables are intended for human
    consumption. Soil amendment with mature organic matter and, in particular, with compost can
    modify metal bioavailability in contaminated soils thus reducing the amount of metals that can be
    uptaken by plants. The determination of Zn distribution inside plant organs may give important
    information to better understand the processes involved in Zn uptake by plants and on the role of
    compost in influencing these processes.

    X-Ray Fluorescence (XRF) microtomography was used to determine the distribution of Zn and
    other elements inside different organs (root, petiole, and leaf) of rocket plants (Eruca vesicaria
    Cavalieri) grown on a soil polluted by 665 mg kg-1 of Zn and amended or not with compost (60 t
    ha-1). Freeze dried plant parts were analysed in full exploiting the high penetration capability of X-
    rays, without the need of cutting thin sections.

    Microtomography experiments were carried out at Beamline L focussing the X-rays at 15-20 µm by
    means of a single bounce capillary (SBC) [1] and using an energy of 13 keV. Roots and petioles
    were rotated over 360° inside the beam with step increments of 3° (Fig. 1). For the leaves, 2D µ-
    XRF maps were collected.

                                        XRF detector
                                                              microscope


                                                                        SBC

                                                    sample             X-rays




                      Figure 1: Experimental set up for XRF microtomography on plant samples

    For plants grown in soil amended with compost, a higher vegetative development was observed as
    well as a lower amount of Zn in the epigeal parts, while Zn concentration in the roots was exactly
    the same for plant grown on the soil amended with compost or on the untreated soil (Tab. 1).

            Table 1: Zn concentration (determined by ICP-OES) and dry weight for different plant organs

                                   Epigeal part:        Roots:          Epigeal part:            Roots:
                                   [Zn] (mg/kg)      [Zn] (mg/kg)       dry weight (g)       dry weight (g)
          No treatment               857±231           456±129            0.12±0.05            0.05±0.05
          Compost 60 t ha-1           527±74            456±77             2.4±1.5              0.5±0.3

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The results obtained using XRF microtomography reveal that, despite an identical Zn
concentration, the two different plant theses show a different Zn distribution inside the root (Fig.
2). In the case of plants grown in the presence of compost, a well defined Zn compartmentalisation
is visible while, in plants grown on the untreated soil, Zn distribution is much more homogeneous.
This observation shows, together with other agronomic parameters (not shown), that plants grown
in polluted soils not amended with compost undergo alterations that cause a reduction in plants
ability to restrict Zn access toward the stele and therefore toward the xylem sap. Also the
distribution observed for some other essential elements (K, Ca, Fe, and S) in the root (not shown)
suggests a reduced capability of plants grown on untreated soils to uptake these important nutrients.
Smaller but still significant differences are also visible in Zn distribution in petioles and leaves.

                                               Compost 60 t ha-1                   No treatment




                                               0.480 mm




                                                                        0.480 mm
                                 2D map
                                                                                                   leaf
                                                             0.795 mm                 0.885 mm


                        XRF tomography
                                               1.220 mm




                                                                        0.915 mm
                                                                                                  petiole
                       XRF tomography
                                               0.975 mm




                                                                        1.320 mm



                                                                                                  root




Figure 2: Zinc distribution in different organs for plants grown in a polluted soil treated with compost or
          untreated.

In conclusion, XRF microtomography revealed to be an extremely powerful tool to look at the
distribution of Zn as well as other important elements inside different plant organs reducing sample
manipulation. The microscopical determination of Zn distribution inside the plant gave important
information to better understand the processes involved in Zn uptake and translocation for plant
grown in soils with or without compost amendment.

µ-XANES experiments performed at the same beamline on living rocket plants supplied other
important data on Zn speciation [2] that, together with Zn distribution, helped to better clarify the
role of compost in influencing Zn uptake and translocation processes.



References
   [1] G. Falkenberg, D.H. Bilderback, and K. Rickers, HASYLAB Annual Report 2003 (2004).
   [2] R. Terzano, Z. Al Chami, B. Vekemans, K. Janssens, T.M. Miano, and Ruggiero P., HASYLAB
       Annual Report 2006 (2007).




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