Root uptake of lipophilic zinc-rhamnolipid complexes

Abstract

This study investigated the formation and plant uptake of lipophilic metal−rhamnolipid complexes. Monorhamnosyl and dirhamnosyl rhamnolipids formed lipophilic complexes with copper (Cu), manganese (Mn), and zinc (Zn). Rhamnolipids significantly increased Zn absorption by Brassica napus var. Pinnacle roots in ⁶⁵Zn-spiked ice-cold solutions, compared with ZnSO₄ alone. Therefore, rhamnolipid appeared to facilitate Zn absorption via a nonmetabolically mediated pathway. Synchrotron XRF and XAS showed that Zn was present in roots as Zn−phytate-like compounds when roots were treated with Zn-free solutions, ZnSO₄, or Zn−EDTA. With rhamnolipid application, Zn was predominantly found in roots as the Zn−rhamnolipid complex. When applied to a calcareous soil, rhamnolipids increased dry matter production and Zn concentrations in durum (Triticum durum L. cv. Balcali-2000) and bread wheat (Triticum aestivum L. cv. BDME-10) shoots. Rhamnolipids either increased total plant uptake of Zn from the soil or increased Zn translocation by reducing the prevalence of insoluble Zn−phytate-like compounds in roots.