ISSN 1021-4437, Russian Journal of Plant Physiology, 2008, Vol. 55, No. 1, pp. 68–76. © Pleiades Publishing, Ltd., 2008.
Pb pollution of soils is a global problem  and has
become a major environmental concern due to its criti-
cal concerns to human and environmental health . Pb
contamination in plant environment is known to cause
highly toxic effects on metabolic processes, inducing
mitotic abnormalities  and leaf chlorosis, exerting
toxic effects on nucleoli , inhibiting root and shoot
growth , reducing photosynthesis , transpiration
, DNA replication , and inhibiting or activating
enzymatic activities .
Because of potential hazards associated with Pb pol-
lution and its wide spreading, an increased attention has
been paid to the development of efﬁcient methods for
: AE—accumulating ecotype; ALAD—
vulinic acid dehydratase; CAT—catalase; Chl—chlorophyll;
CK—control; MDA—malondialdehyde; NAE—non-accumulat-
ing ecotype; NBT—nitroblue tetrazolium; OsO
oxide; PBS—phosphate-buffered saline; PVP—polyvinylpyrroli-
done; SOD—superoxide dismutase; TBA—thiobarbituric acid.
This text was submitted by the authors in English.
cleaning up the environment from Pb with the mini-
mum side effects . Phytoremediation of heavy
metal-contaminated soil is an emerging technology that
aims to extract or inactivate metals in soils . Cur-
rently it has grabbed more attention due to the low cost
of implementation and environmental beneﬁts.
An increased interest was manifested to the identiﬁ-
cation of autochthonous plant species that can accumu-
late elevated amounts of heavy metals in their tissues,
with the aim of employing them for phytoremediation
of contaminated soils [11–15]. There are ﬁve recog-
nized Pb hyperaccumulator plant species , in which
Pb concentration exceeds 0.1% of dry weight; they are:
Armeria martima, Thlaspi rotundifolium, Th. alpestre,
However, these plant species are not suited for phytoex-
traction of Pb from contaminated soils because of their
slow growth and low biomass .
Hance is a newly discovered Zn/Cd
hyperaccumulator growing in the old Pb/Zn mined
areas of south-east China and proved to be a Pb accu-
Effect of Pb on Leaf Antioxidant Enzyme Activities
and Ultrastructure of the Two Ecotypes of
, T. Q. Li
, X. E. Yang
, E. Islam
, X. F. Jin
, and Q. Mahmood
Key Laboratory of Environmental Remediation and Ecosystem Health, Ministry of Education, College of Natural Resources
and Environmental Science, Zhejiang University, Huajiachi Campus, Hangzhou, 310029 China;
fax: +86-571-86971907; e-mail: email@example.com; firstname.lastname@example.org
School of Tourism and Health, Zhejiang Forestry College, Lin’an, 311300 China
Department of Botany, Federal Government Postgraduate College, H-8, Islamabad, Pakistan
Received January 13, 2007
—Hydroponic experiments were conducted to study the effect of Pb on growth, leaf antioxidant
enzyme activities, and ultrastructure of the accumulating ecotype (AE) and non-accumulating ecotype (NAE)
Hance. AE was found to be more tolerant to excessive Pb levels in growth medium. Concen-
trations of Pb in the shoots of the AE were 1.98 times higher than those in the NAE when 0.2 mM Pb was sup-
plied. Both chlorophyll
did not decrease signiﬁcantly in AE plants after Pb treatment, while a signiﬁcant
decrease was noted in chlorophyll
of NAE plants treated with Pb concentrations greater than 0.05 mM.
The results showed that activities of superoxide dismutase (SOD) and catalase (CAT) were elevated in the
leaves of AE under Pb stress. However in NAE, Pb-caused enhancement was noticed only in the activity of SOD
while activity of CAT was declined as compared to the control plants. With increased Pb level, malondialdehyde
(MDA) content increased signiﬁcantly in both ecotypes of
indicating that Pb toxicity led to lipid per-
oxidation and membrane damage, but MDA content in the leaves of NAE was always higher than in AE plants.
The ultrastructural analysis of the spongy mesophyll cells revealed that excessive Pb concentrations obviously
damaged the cell membrane, chloroplasts, and mitochondria of both the ecotypes but damage was more severe
in NAE. Although growth, leaf physiology, and ultrastructure of both the ecotypes were affected by Pb treat-
ment, deleterious effects were more pronounced in NAE.
Key words: Sedum alfredii - antioxidant enzymes - Pb toxicity - phytoremediation - transmission electron