Iron (Fe) allocation in leaves of Fe-deficient cucumber
plants fed hydroponically with natural Fe-complexes
1
2
2
3
3
3
3
R. Terzano , M. Alfeld , K. Janssens , N. Tomasi , S. Gottardi , R. Pinton , S. Cesco and
1
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
3 Dip. di Scienze Agrarie e Ambientali, University of Udine, Via delle Scienze 208, I-33100 Udine, Italy
Due to the very limited solubility of Fe, soluble Fe sources available in soil for plant nutrition are
mainly represented by a mixture of complexes between the micronutrient and organic ligands such
as organic acids, phytosiderophores (PS), microbial siderophores as well as fractions of humified
organic matter [1].
In this research, Fe translocation and allocation into the leaves of plants grown in hydroponic
solution after the addition of different natural Fe-complexes were investigated, beside other
techniques, by synchrotron 2D-scanning µ-XRF. These analyses were carried out at Beamline L
focusing the X-rays to a 20 µm2 X-ray beam and using an energy of 14 keV. The experimental setup
consisted of a multilayer monochromator, a polycapillary lens and two detectors placed at both
sides of the sample, each at 90° to the incoming beam. An Al filter was placed in front of the
detectors to reduce the intensity of the fluorescent radiation from low Z elements such as Ca and K,
thus improving the signal for higher Z trace elements, especially Fe (Fig. 1).
Figure 1: Experimental setup for 2D-scanning µ-XRF on cucumber leaves.
In particular, dynamics of Fe allocation after 1 and 5 days were studied by imaging Fe distribution
in 3 mm × 2 mm areas on freeze dried fully expanded leaves of intact Fe-deficient cucumber plants
supplied with different natural Fe-complexes, i.e. Fe-citrate, Fe-PS, and Fe complexed to waterextractable humic substances (Fe-WEHS) [2].
Total Fe concentration in the leaves was assessed by ICP-AES, after total acid digestion of the
sample, and by 59Fe liquid scintillation after treatment of the plants with 59Fe complexed by the
natural sources. Results reported in Fig. 2 show that Fe amount in the leaves of plants fed with FeWEHS was higher than those measured in the leaves of plants treated with Fe-citrate or Fe-PS.
a
■ Fe-WEHS
О Fe-PS
∆ Fe-Citrate
µg59Fe g-1 DW
µgFe g-1 DW
b
Time (d)
■ Fe-WEHS
О Fe-PS
∆ Fe-Citrate
Time (d)
Figure 2: Fe concentration in leaves as determined by ICP-AES (a) or liquid scintillation (b)
The higher capacity of cucumber plants to acquire Fe when fed with Fe-WEHS, was also confirmed
by µ-XRF maps. Beside other information, the process of charging and discharging of Fe in the
main leaf veins after 1 or 5 days from Fe-supply could be clearly visualised by µ-XRF, as reported
in Fig. 3.
a
b
Figure 3: Fe distribution in the central part of leaves treated with Fe-WEHS after 1d (a) or 5d (b)
Synchrotron X-ray microbeam techniques are being used to study Fe distribution and concentration
inside different plant species grown in the presence of various Fe sources, in order to evaluate the
efficiency of new natural Fe-chelates compounds to be employed in agriculture [3].
References
[1] W.L. Lindsay and A.P. Schwab. J. Plant Nutr. 5, 821 (1982).
[2] S. Cesco, M. Nikolic, V. Römheld et al., Plant Soil 241, 121 (2002).
[3] R. Terzano, M. Spagnuolo, P. Ruggiero et al., HASYLAB Annual Report 2007, 1513 (2008).