Format: ORAL

Maggie-Anne Harvey1, Jeroen van der Woude1, Ai Lin1, Abel Muller1, Cyril Stevens1, Mirko Salinitro2, Dennis Brueckner3, Hugh H. Harris4, Kathryn M. Spiers3, James H. Lovett4, Antony van der Ent1

1 Wageningen University and Research, Wageningen, The Netherlands. 2 University of Bologna, Bologna, Italy. 3 Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany. 4 The University of Adelaide, Adelaide, Australia.

Selenium (Se) is an element beneficial but not essential to plant nutrition, and soils enriched with Se are typically hostile to plant growth and induce toxicity. Uniquely adapted hyperaccumulator plants are capable of growing on these enriched soils and accumulating rather extreme concentrations of Se in their tissues, without exhibiting serious toxicity. In Australia, the legume Neptunia amplexicaulis was found growing on seleniferous soils with 4400 g Se g-1 in its tissues, and under controlled conditions this plant is capable of concentrating up to 13,600 g Se g-1 in the youngest leaves. This plant has been shown to retain and circulate its accumulated Se, concentrating Se in phloem sinks such as developing tissues and recycling Se as these phloem sinks become phloem sources. While Se is generally metabolized into a non-toxic organic form (selenocystathioinine), concentrating excessive Se can be a metabolically costly and risky process. Recently we have been able to use cutting edge X-Ray Fluorescence Tomographic Imaging at the German Synchrotron (DESY) to examine the tissue distribution of Se in phloem sinks. These tissues, such as the youngest developing leaves, apical meristem and root tips, would have been difficult to hand section without damaging the tissues or losing any phloem-bound Se. It was found that Se is present in the epidermis of the youngest leaves unlike maturing leaves, less Se could be found in the vascular tissues of these developing organs. In contrast, the root tips showed ubiquitous Se concentrations in the ground meristem, with a gradual concentration of Se in vascular tissues as they begin to develop. Analysis of this distribution can reveal interesting implications about the mechanisms of Se cycling in this plant, as well as the evolutionary advantages of Se hyperaccumulation.