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Spatial distribution and speciation of copper in root tips of cucumber revealed by μ-XRF and μ-XANES

J. Song, Y. Q. Yang, S. H. Zhu, G. C. Chen, X. F. Yuan, T. T. Liu, X. H. Yu, J. Y. Shi
Biologia plantarum 2013 v.57 no.3 pp. 581-586
Cucumis sativus, X-radiation, absorption, biotransformation, cell walls, chemical speciation, citrates, copper, cucumbers, cytoplasm, fluorescence, meristems, root cap, root tips
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 root cap and meristematic zone whereas low Cu content in elongation and maturation zone. There was a dramatic increase of Cu content in root cap and meristematic zone after treatment with 100 μM CuSO₄ for 72 h. The μ-XANES analysis revealed that most of Cu in root tip was bound with alginate, citrate, and cysteine-like ligands whereas rarely deposited in form of CuO. From 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 root cap to elongation zone but sharply declined in maturation zone. The results suggested that Cu was chelated by S ligands in the cell walls which protect protoplasm against possible damage caused by Cu excess.