The localization, biotransformation, and chemical speciation of copper in root tips of cucumber (Cucumis sativus) were investigated using synchrotron-based micro X-ray fluorescence (µ-XRF) and micro X-ray absorption near edge structure (µ-XANES). The highest content of Cu was found in a root cap and meristematic zone whereas low Cu content in elongation and maturation zones. There was a dramatic increase of Cu content in a root cap and meristematic zone after treatment with 100 µM CuSO 4 for 72 h. The µ-XANES analysis revealed that most Cu in a root tip was bound with alginate, citrate, and cysteine-like ligands whereas rarely deposited in form of CuO. From a root cap to maturation zone, the proportion of Cu bound with alginate-like ligands increased whereas that bound with citrate-like ligands decreased. The proportion of Cu bound with cysteine-like ligands increased from a root cap to elongation zone but sharply declined in maturation zone. The results suggest that Cu was chelated by S ligands in the cell walls which protect protoplasm against possible damage caused by Cu excess.

No abstract

No abstract