4.3.4 Effect of Cd on ROS Generation
Heavy metals cause oxidative damage to plants, either directly or indirectly
through reactive oxygen species (ROS) formation. Cd is a non-redox metal that
does not produce ROS such as the superoxide anion (O 2 •–), singlet oxygen (
1 O 2 ),
hydrogen peroxide (H 2 O 2 ), and hydroxyl radical (OH•) but generates oxidative
stress by interfering with the antioxidant defense system (Benavides et al. 2005;
Gratão et al. 2005). However, Cd could lead to the generation of ROS indirectly by
production of a disturbance in the chloroplasts. In addition, other reports suggested
that Cd may stimulate the production of ROS in the mitochondrial electron transfer
chain (Heyno et al. 2008). The manifestations of ROS damages in plants involve
lipid peroxidation, protein peroxidation, and DNA damage. Cd produced an
enhancement of lipid peroxidation in Phaseolus vulgaris (Chaoui et al. 1997),
Helianthus annuus (Gallego et al. 1996), and Pisum sativum (Lozano-Rodriguez
et al. 1997). DNA damage caused by Cd involved destruction of nucleic acids, cell
membrane, lipids, and proteins, reduction of protein synthesis, and damage of
photosynthetic proteins, affecting growth and development of the whole organism
(Gill and Tuteja 2010; Kranner and Colville 2011). Cadmium toxicity leads to
variation in the activity of scavengers of superoxide and hydrogen peroxide such as
superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidases (POD), and glutathione reductase (GR) (Sandalio et al. 2001; Milone
et al. 2003). Besides this proline accumulation appeared to be a suitable indicator
of heavy metal stress. Islam et al. (2009) reported that tobacco cells exposed to Cd
treatment accumulated high levels of proline, and by this way they can alleviate the
inhibitory effect of Cd on cell growth.
4.3.5 Effect of Cd on Stress Proteins
Heat-shock proteins (HSPs) are presently known as proteins that have functions to
resist stress in eukaryotes. In Cd-treated maize plants, a synthesis of 70 kDa phosphoprotein (HSP) was reported by Reddy and Prasad (1993). In Cd-treated pea
plants, pathogen-related proteins PrP4A and HSP71 were found, and they probably
serve to protect cells against damages induced by Cd (Rodríguez-Serrano et al.
2006). In wheat, seedlings treated with 50 μM CdCl2 for 48 h, a 51 kDa soluble
protein was found. This protein was designated as a Cd stress-associated protein. It
was generated mainly in the root tissue of treated and control seedlings and located
below the plasma membrane and outer periphery of the tonoplast (Mittra et al. 2008).
In poplar (Populus tremula ) exposed to Cd for a short-term (14 days) or a longerterm (56 days) treatment, it was found that stress-related proteins, like HSPs, proteinases, and pathogenesis-related proteins, increased in abundance in leaves,
whereas most of the proteins from the primary metabolism (tricarboxylic acid
cycle, nitrogen metabolism, and sulfur metabolism) were severely decreased in
abundance (Kieffer et al. 2009).
15 Cadmium as an Environmental Pollutant: Ecotoxicological Effects, Health. . .
369
Heavy metals cause oxidative damage to plants, either directly or indirectly
through reactive oxygen species (ROS) formation. Cd is a non-redox metal that
does not produce ROS such as the superoxide anion (O 2 •–), singlet oxygen (
1 O 2 ),
hydrogen peroxide (H 2 O 2 ), and hydroxyl radical (OH•) but generates oxidative
stress by interfering with the antioxidant defense system (Benavides et al. 2005;
Gratão et al. 2005). However, Cd could lead to the generation of ROS indirectly by
production of a disturbance in the chloroplasts. In addition, other reports suggested
that Cd may stimulate the production of ROS in the mitochondrial electron transfer
chain (Heyno et al. 2008). The manifestations of ROS damages in plants involve
lipid peroxidation, protein peroxidation, and DNA damage. Cd produced an
enhancement of lipid peroxidation in Phaseolus vulgaris (Chaoui et al. 1997),
Helianthus annuus (Gallego et al. 1996), and Pisum sativum (Lozano-Rodriguez
et al. 1997). DNA damage caused by Cd involved destruction of nucleic acids, cell
membrane, lipids, and proteins, reduction of protein synthesis, and damage of
photosynthetic proteins, affecting growth and development of the whole organism
(Gill and Tuteja 2010; Kranner and Colville 2011). Cadmium toxicity leads to
variation in the activity of scavengers of superoxide and hydrogen peroxide such as
superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidases (POD), and glutathione reductase (GR) (Sandalio et al. 2001; Milone
et al. 2003). Besides this proline accumulation appeared to be a suitable indicator
of heavy metal stress. Islam et al. (2009) reported that tobacco cells exposed to Cd
treatment accumulated high levels of proline, and by this way they can alleviate the
inhibitory effect of Cd on cell growth.
4.3.5 Effect of Cd on Stress Proteins
Heat-shock proteins (HSPs) are presently known as proteins that have functions to
resist stress in eukaryotes. In Cd-treated maize plants, a synthesis of 70 kDa phosphoprotein (HSP) was reported by Reddy and Prasad (1993). In Cd-treated pea
plants, pathogen-related proteins PrP4A and HSP71 were found, and they probably
serve to protect cells against damages induced by Cd (Rodríguez-Serrano et al.
2006). In wheat, seedlings treated with 50 μM CdCl2 for 48 h, a 51 kDa soluble
protein was found. This protein was designated as a Cd stress-associated protein. It
was generated mainly in the root tissue of treated and control seedlings and located
below the plasma membrane and outer periphery of the tonoplast (Mittra et al. 2008).
In poplar (Populus tremula ) exposed to Cd for a short-term (14 days) or a longerterm (56 days) treatment, it was found that stress-related proteins, like HSPs, proteinases, and pathogenesis-related proteins, increased in abundance in leaves,
whereas most of the proteins from the primary metabolism (tricarboxylic acid
cycle, nitrogen metabolism, and sulfur metabolism) were severely decreased in
abundance (Kieffer et al. 2009).
15 Cadmium as an Environmental Pollutant: Ecotoxicological Effects, Health. . .
369