XAS and microscopy studies of the uptake and bio-transformation of copper in Larrea tridentata (creosote bush)

Herein we present work directed toward understanding the mechanisms employed by Larrea tridentata (Creosote bush) to uptake and simultaneously defend against the presence of excess copper. The location and nature of copper in the plant have been studied on several length scales: greater than 10 mum (scanning electron microscopy), less than 10 mum (transmission electron microscopy) and atomic level structure and speciation (EXAFS and XANES). Two interesting results are apparent: creosote takes up or adsorbs copper from the soil in the Cu(II) oxidation state and transports it to the leaves where copper is found as Cu(I) and Cu(II). The transport agent appears to be a Cu phytochelatin. Additionally, creosote may be immobilizing and excreting copper via at least two additional mechanisms: storage of metals in vacuoles and excretion of copper into the sticky resinous substance found on the leaf surface. Creosote may also accumulate wind-blown particulates that can easily adhere to the resinous sticky surface of the plant. If, however, the particulates are < 10 <mu>m they may enter the leaf by respiration through the plant 'stomata' that have openings between 5 mum and 10 mum As such, creosote may be a natural bio-indicator for airborne particulates that are < 10 <mu>m. (C) 2000 Elsevier Science B.V. All rights reserved.