ISSN 1021-4437, Russian Journal of Plant Physiology, 2007, Vol. 54, No. 3, pp. 381–387. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © A.S. Lukatkin, N.V. Gracheva, N.N. Grishenkova, P.V. Dukhovskis, A.A. Brazaitite, 2007, published in Fiziologiya Rastenii, 2007, Vol. 54, No. 3, pp. 432–439.
Plant life conditions on the Earth are gradually
worsening due to global processes of natural and
anthropogenic origin. Therefore, precise assessment of
plant adaptive potential becomes a new challenge. This
problem cannot be solved without studying plant resis-
tance to injuring treatments.
Heavy metals (HM) are among the most important
stressors acting on plants. The problem of “metallic
pressure” on biosphere is aggravated by the longevity
of HM retention in the turnover of organic matter.
Another important factor is a rapid and progressively
increasing supply of HM into the biosphere. The tech-
nogenic migration of heavy metals can disrupt metabo-
lism and physiological functions of the organism,
diminish plant productivity, and alter the ecosystem
structure and species diversity .
Some heavy metals (including Fe, Cu, Zn, Ni, etc.)
participate in many physiological processes in higher
plants [2, 3]. However, the elements with rare occur-
rence in the Earth’s crust are often toxic for plants, and
their effects on cell metabolism are quite diverse owing
to direct and indirect action of HM .
Various metals are differentially toxic for plants.
The most dangerous species are Cd, Cu, Pb, and Cr;
their toxic action on plants is studied quite well. At the
same time, effects of less toxic but potentially danger-
ous species—Ni and Zn—are not investigated in detail,
in spite of their appreciable inﬂuence on plant growth
and physiological processes [5–10]. For example, the
excess of nickel suppressed the mitotic activity in
maize root apex and disturbed the integrity of root mer-
istems ; it also inhibited growth of roots and shoots
in some plant species [6–8, 10]. The excess of zinc per-
turbed iron uptake and metabolism, inhibited photosyn-
thesis and respiration , impeded growth and biomass
accumulation, reduced the content of chlorophyll and
carotenoids, and lowered the activity of nitrate reduc-
A hypothesis is currently emerging that excessive
doses of HM induce oxidative stress in plant cells [7,
11]. The cells of wheat plants treated with HM were
found to produce reactive oxygen species (ROS) .
Subsequent ROS-mediated processes developed to var-
ious extents, depending on localization, temporal pat-
tern, and the content of stress-induced ROS , as
well as on the rate of ROS inactivation by cellular
defense systems. Among ROS-inactivating systems,
ascorbate plays a dominant role . In plant cells it
and donates electrons to ascor-
bate peroxidase (APO), the principal enzyme of
detoxiﬁcation [14, 15].
Biologically active substances can modulate plant
responses to stress factors. Synthetic growth regulators
occupy a special place among these agents. However,
only few works dealt with the effects of growth regula-
tors on HM-treated plants. For example, kinetin was
Cytokinin-Like Growth Regulators Mitigate Toxic Action of Zinc
and Nickel Ions on Maize Seedlings
A. S. Lukatkin
, N. V. Gracheva
, N. N. Grishenkova
, P. V. Dukhovskis
, and A. A. Brazaitite
Department of Botany and Plant Physiology, Faculty of Biology, Ogarev Mordovian State University,
Bolshevistskaya ul. 68, Saransk, 430000 Russia;
Lithuanian Institute of Horticulture, Babtai, Lithuania
Received November 29, 2005
L.) seedlings grown in water culture in the presence of zinc and nickel ions were
used with an effort to alleviate heavy metal toxicity by treating seeds with thidiazuron and kinetin (synthetic
growth regulators with cytokinin-like activity). Heavy metals were shown to decrease germinability of seeds,
suppress seedling growth, alter membrane permeability, and inhibit the activity of ascorbate peroxidase. Syn-
thetic cytokinin-like agents alleviated deteriorative effects of heavy metals; the extent of alleviation depended
on toxicant species and its concentration. The toxic effect of Zn
was effectively relieved by kinetin, whereas
toxicity was preferentially alleviated by thidiazuron.
Key words: Zea mays - growth characteristics - electrolyte leakage - ascorbate peroxidase - heavy metals - zinc -
nickel - thidiazuron - kinetin
: APO—ascorbate peroxidase; HM—heavy metals;
ROS—reactive oxygen species.