15th-16th March, 2017: 18th Japan Mossbauer Spectroscopy Forum Symposium, Tokyo, Japan

[Z. Klencsar]

The 18th Japan Mossbauer Spectroscopy Forum Symposium was held during the days of 15-16 March, 2017, at the Tokyo University of Science, Tokyo, Japan. At the conference Krisztina Kovács presented a lecture dealing with the identification of Fe compounds formed in the roots of iron deficient test plants supplied either with Fe2+-ascorbate or Fe3+-citrate.

Investigation of the main chemical factors influencing the effectiveness of iron uptake in plants - a Mössbauer spectroscopic study

K. Kovács 1, M. Óvári 2, Á. Solti 3, F. Fodor 3
1 Laboratory of Nuclear Chemistry, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter 1/A, 1117 Budapest, Hungary
2 Danube Research Institute, Hungarian Academy of Sciences, Karolina 29, 1113 Budapest, Hungary
3 Department of Plant Physiology and Molecular Plant Biology, Eötvös Loránd University, Pázmány Péter 1/C, 1117 Budapest, Hungary

Despite being the fourth most abundant element in the earth's crust, Fe is not readily available for plants due to the low solubility of iron oxides at the pH of many soils. The low bioavailability of iron causes a common nutritional disorder that alters plant morphology and physiology even prompting plant death (Briat, 2007). To cope with this problem, Fe can be supplied as synthetic or natural Fe complexes applied in soils (Lucena, 2000). However, it is rather difficult to predict the effectiveness of such Fe-complexes. For this reason, the knowledge on Fe speciation, redox transitions in the presence of plant-associated organic compounds (ascorbic acid, citric acid, phenolics), are of great importance. In the present work, Fe compounds formed in roots of iron deficient test plants belonging to both Strategy I and II iron uptake mechanisms, were studied with Mössbauer spectroscopy. Iron was supplied either in +2 oxidation state (Fe2+-ascorbate) or in +3 oxidation state (Fe3+-citrate, Fe3+-phenolics). Mössbauer results were completed with the measurement of the total iron concentration and with physiological measurements.

Typical Mössbauer spectrum of iron deficient roots supplied with Fe2+-ascorbate or Fe3+-citrate shows the presence of both Fe3+ and Fe2+ species. The Fe3+-components could be identified as mainly high spin Fe3+-carboxylate complexes while Fe2+ could be attributed to high spin Fe2+-hexaaqua complex and Fe2+ bound to the cell wall (Kovács et al. 2016). The relative amount of the Fe3+ depends on both the concentration and the duration of iron supply. Moreover, from the ratio of Fe2+/Fe3+, the reoxidation rate of Fe2+ to Fe3+ during the Fe uptake process could be estimated. Signifıcant differences were found in the Fe2+/Fe3+ concentrations in the case of test plants belonging to different iron uptake strategies. In addition, the application of divalent and trivalent iron sources resulted in different physiological status of the photosynthetic apparatus indicating that the effectiveness of iron supply strongly depends on the oxidation state of iron. The results obtained can help to improve the current state of knowledge on the factors that influence the efficiency of iron fertilizers and thus, to help in finding new, effective compounds which can be further used as iron supply for plants.

Acknowledgement
This study was carried out with the fınancial support of NKFIH (project No. PD 111979, PD 112047, K 115913).

References
Briat, J.F. 2007 Advances in botanical research. Academic, London, UK, Vol 46, 138-169.
Lucena, J.J. 2000 J. Plant Nutr. 23: 1591-1606
Kovács K., Pechoušek J., Machala, L., Zboril, R., Klencsár Z., Solti, Á.. Tóth, B., Müller, B., Pham, HD., Kristóf, Z., Fodor, F. 2016 Planta, 244: 167-179.