Mimosine facilitates Fe uptake by Leucaena leucocephala subsp. glabrata in alkaline soils by solubilizing Fe-oxides

Purpose Giant leucaena is a tropical tree-legume that thrives in alkaline and calcareous soils. It contains large amounts of mimosine, the physiological role of which is not well understood. The goals of this study were to determine i) if mimosine is released by giant leucaena into the rhizosphere ii) if mimosine enhances solubility of Fe present in various forms in alkaline soil, and iii) if mimosine enhances transition metal uptake in giant leucaena. Methods Mimosine in the extracts of rhizosphere soil and root exudates was analyzed by high performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) to determine if it is released by giant leucaena. Iron concentration in tissue and aqueous samples was determined by ICP-OES analysis. Results Mimosine was detected in both the rhizosphere eluates and root exudates. Mimosine added to samples of goethite, hematite and FeCl3 increased Fe solubility in water. Giant leucaena plants grown in alkaline soils and supplied with mimosine had higher levels of chlorophyll, Fe and Mn than the control plants. Conclusion Mimosine is released by giant leucaena roots into the rhizosphere, where it interacts with Fe. Mimosine enhances solubility of insoluble Fe-oxides and prevents conversion of ferric Fe to insoluble oxides at an alkaline pH. Mimosine enhances Fe and Mn uptake in plants growing in alkaline soil conditions.