plants by influx and efflux system, respectively, thus enhances the translocation
across different tissues and cells (Bakhat et al. 2017; Ma et al. 2007; Ma and Yamaji
2006). Furthermore, the As speciation and its translocation/adsorption in plants are
also controlled by physicochemical properties and plant physiological tolerance
mechanisms under stress (Khalid et al. 2017). Plants are well equipped with tolerance mechanisms by biological and biochemical mechanisms that play a crucial role
in the As speciation and translocation from roots to shoots (Pourrut et al. 2011).
Thus, the physiological fluctuations within plants could also alter As translocation/
uptake by plants.
5 Arsenic Toxicity: Effects on Plant Metabolism
Worldwide, Arsenic (As) contamination is an important concern in human food
chain which is not restricted by any economic boundaries. Rice grain is one of the
major sources of human As outside of contaminated drinking water (Meharg et al.
2009). Arsenic (As)-contaminated rice samples were collected from different parts of
the world. As was found to be distributed normally in samples from developing
economic countries, but in developed countries samples of As contents were high
(Meharg et al. 2009). Therefore, eradication of the accumulation of As in rice grain is
one of the important research objective. Arsenic is nonessential and primarily toxic
to plants. In plants, the roots are the first tissue to be affected by As, where the
metalloid prevents root growth and its proliferation. Upon translocation to the shoot,
As can severely obstruct plant growth by slowing down or apprehend development
and biomass accumulation, as well as compromising plant reproductive capacity
through losses in fertility, yield, and fruit production (reviewed by Garg and Singla
2011). High concentration of As plays a major role in metabolic processes, which
will affect plant growth leading to death. The majority of plants will retail As content
in their roots. Nevertheless, As translocation to the shoot and other parts of the plant
is based on the genotype. Various physiological progressions are vulnerable to As
toxicity. Plants which are exposed to As lead to cellular membrane damage and
electrolyte leakage (Singh et al. 2006). In plants, membrane damage is regularly
coincided by an increase in malondialdehyde, a product of lipid peroxidation,
indicating to the role of oxidative stress in As toxicity. Arsenic exposure to plants
induces antioxidant defense mechanisms. The synthesis of ascorbate, the γ-Glu-CysGly tripeptide glutathione (GSH), and the GSH oligomer (γ-Glu-Cys)n-Gly)
phytochelatin (PC) increases throughout the plant, but particularly in the roots
(Schmöger et al. 2000; Li et al. 2004; Geng et al. 2006; Singh et al. 2006; Khan
et al. 2009), whereas anthocyanin accumulates in the leaves (Catarecha et al. 2007).
Low As burden causes the number of nitrogen-fixing root nodules to be repressed in
soybean (Vázquez et al. 2008). The molecular mechanisms underlying above physiological responses to As exposure are not well studied, but have of late attracted
increased attention. Paradoxes related to As toxicity will stimulate the plant growth
in lower As concentrations (Miteva 2002; Garg and Singla 2011). In Arabidopsis
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P. Narayanasamy and R. K. Subramanian
across different tissues and cells (Bakhat et al. 2017; Ma et al. 2007; Ma and Yamaji
2006). Furthermore, the As speciation and its translocation/adsorption in plants are
also controlled by physicochemical properties and plant physiological tolerance
mechanisms under stress (Khalid et al. 2017). Plants are well equipped with tolerance mechanisms by biological and biochemical mechanisms that play a crucial role
in the As speciation and translocation from roots to shoots (Pourrut et al. 2011).
Thus, the physiological fluctuations within plants could also alter As translocation/
uptake by plants.
5 Arsenic Toxicity: Effects on Plant Metabolism
Worldwide, Arsenic (As) contamination is an important concern in human food
chain which is not restricted by any economic boundaries. Rice grain is one of the
major sources of human As outside of contaminated drinking water (Meharg et al.
2009). Arsenic (As)-contaminated rice samples were collected from different parts of
the world. As was found to be distributed normally in samples from developing
economic countries, but in developed countries samples of As contents were high
(Meharg et al. 2009). Therefore, eradication of the accumulation of As in rice grain is
one of the important research objective. Arsenic is nonessential and primarily toxic
to plants. In plants, the roots are the first tissue to be affected by As, where the
metalloid prevents root growth and its proliferation. Upon translocation to the shoot,
As can severely obstruct plant growth by slowing down or apprehend development
and biomass accumulation, as well as compromising plant reproductive capacity
through losses in fertility, yield, and fruit production (reviewed by Garg and Singla
2011). High concentration of As plays a major role in metabolic processes, which
will affect plant growth leading to death. The majority of plants will retail As content
in their roots. Nevertheless, As translocation to the shoot and other parts of the plant
is based on the genotype. Various physiological progressions are vulnerable to As
toxicity. Plants which are exposed to As lead to cellular membrane damage and
electrolyte leakage (Singh et al. 2006). In plants, membrane damage is regularly
coincided by an increase in malondialdehyde, a product of lipid peroxidation,
indicating to the role of oxidative stress in As toxicity. Arsenic exposure to plants
induces antioxidant defense mechanisms. The synthesis of ascorbate, the γ-Glu-CysGly tripeptide glutathione (GSH), and the GSH oligomer (γ-Glu-Cys)n-Gly)
phytochelatin (PC) increases throughout the plant, but particularly in the roots
(Schmöger et al. 2000; Li et al. 2004; Geng et al. 2006; Singh et al. 2006; Khan
et al. 2009), whereas anthocyanin accumulates in the leaves (Catarecha et al. 2007).
Low As burden causes the number of nitrogen-fixing root nodules to be repressed in
soybean (Vázquez et al. 2008). The molecular mechanisms underlying above physiological responses to As exposure are not well studied, but have of late attracted
increased attention. Paradoxes related to As toxicity will stimulate the plant growth
in lower As concentrations (Miteva 2002; Garg and Singla 2011). In Arabidopsis
244
P. Narayanasamy and R. K. Subramanian