La. Polette et al., XAS and microscopy studies of the uptake and bio-transformation of copper in Larrea tridentata (creosote bush), MICROCHEM J, 65(3), 2000, pp. 227-236
Herein we present work directed toward understanding the mechanisms employe
d 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 mic
roscopy) and atomic level structure and speciation (EXAFS and XANES). Two i
nteresting results are apparent: creosote takes up or adsorbs copper from t
he 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 C
u phytochelatin. Additionally, creosote may be immobilizing and excreting c
opper via at least two additional mechanisms: storage of metals in vacuoles
and excretion of copper into the sticky resinous substance found on the le
af surface. Creosote may also accumulate wind-blown particulates that can e
asily 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, cr
eosote may be a natural bio-indicator for airborne particulates that are <
10 <mu>m. (C) 2000 Elsevier Science B.V. All rights reserved.