Agriculture Reference
In-Depth Information
silver (Ag), selenium (Se) and zinc (Zn) (Long et al.
2002
). Contamination of
arable soil with Cd is one of the most serious agricultural problems in the world,
and therefore it is considered to be one of the most toxic elements to plants, animals
and human beings. Due to its high solubility in water, it is promptly taken up by
plants and this represents the main entry pathway into the food chain (Metwally
et al.
2005
; Farinati et al.
2010
).
The agricultural soil may have toxic levels of heavy metals due to various an-
thropogenic activities (Xie et al.
2006
; Alkorta et al.
2004
; Verma et al.
2007
; Wei
and Zhou
2008
). It has been estimated that the heavy metal concentration in soil
typically ranges from less than one to as high as 100,000 mg kg
−1
. Kamnev and Van
der Lelie (
2000
) reported that ~9.9-45.0 tons of Cd is discharged into the soil every
year globally, which is one of the most highly toxic environmental pollutant in the
atmosphere, soil and water, and in excessive amounts can cause serious problems to
all organisms (Benavides et al.
2005
). Even at low concentration, significant reduc-
tion in plant growth and biomass has been reported in the literature (Sanita di Toppi
and Gabbrielli
1999
; Sandalio et al.
2001
; Dominguez et al.
2003
; Drazkiewicz and
Baszynski
2005
; Gianazza et al.
2007
; Singh et al.
2008
). The regulatory limit of Cd
in agricultural soil is 100 mg kg
−1
soil (Salt et al.
1995
) but this threshold is continu-
ously exceeding because of various anthropogenic activities. Cd is toxic for most
of the plants at concentrations greater than 5-10 μg Cd g
−1
leaf dry weight (White
and Brown
2010
), except for Cd-hyperaccumulators, which can tolerate Cd con-
centrations of 100 μg Cd g
−1
leaf dry weight (Verbruggen et al.
2009
). Furthermore,
significantly higher levels of Cd in the agricultural soil lead to the degradation of
soil quality, loss of crop productivity as well as poor quality of agricultural products
(Long et al.
2002
), which pose significant hazards to human, animal, and ecosystem
health (Blaylock and Huang
2000
).
Cadmium has no biological function and is not even essential for plant growth.
Being water soluble, it can be easily absorbed in tissues and can cause various phy-
totoxic visible symptoms, which include leaf chlorosis, root putrescence, growth
inhibition which ultimately cause plant death (Skrzyska-Polit et al.
2010
; Valent-
oviová et al. 2010). Cadmium causes inhibition of shoot and root growth (Schut-
zendubel et al.
2001
), disorganization of the grana structures and reduction in the
biosynthesis of chlorophyll (Somashekaraiah et al. 1992; Siedlecka and Krupa
1996
). It also interferes with photosynthesis, respiration and water relations (Per-
fus-Barbeoch et al.
2002
; Balakhnina et al.
2005
; Mobin and Khan
2007
; Singh
et al.
2008
; Gill et al.
2011
). Moreover, it can also inhibit the activity of several
groups of enzymes, such as those of the photosynthetic Calvin cycle (Sandalio et al.
2001
), carbohydrate metabolism (Sanita di Toppi and Gabbrielli
1999
; Verma and
Dubey
2003
) and phosphorus metabolism (Shah and Dubey
1998
; Sharma and
Dubey
2007
). Cadmium is known to cause the generation of reactive oxygen spe-
cies (ROS), which leads to oxidative stress in plant tissues (Skorzynska-Polit et al.
2003
/2004; Romero-Puertas et al.
2004
; Mobin and Khan
2007
; Gill and Tuteja
2010
). The presence of Cd-lead high concentration of ROS causes oxidative dam-
age to photosynthetic pigments, bio-molecules such as lipids, proteins and nucleic
acids, leakage of electrolytes via lipid peroxidation resulting in dramatic reductions
