silicon has been also found to support the plant in nutrient deficiency stress
conditions as well as toxicity; for example, calcium (Mali and Aery 2008; Etesami
and Jeong 2018; Dong et al. 2018; do Nascimento et al. 2020), magnesium (Hosseini
et al. 2019; do Nascimento et al. 2020), boron (Savić and Marjanović-Jeromela
2013; Liu et al. 2017; Metwally et al. 2018; Pereira de Souza Junior et al. 2019;
Oliveira et al. 2020), iron (You-Qiang et al. 2012; Pavlovic et al. 2013; Bityutskii
et al. 2014; Patil et al. 2018; do Nascimento et al. 2020; dos Santos et al. 2020),
manganese (Dragišić Maksimović et al. 2007; Patil et al. 2018; de Oliveira et al.
2019; do Nascimento et al. 2020), zinc (Gu et al. 2012; Bityutskii et al. 2014;
Hernandez-Apaolaza 2014; Pascual et al. 2016; do Nascimento et al. 2020; Raj
et al. 2020), copper (Frantz et al. 2011; Patil et al. 2018; Raj et al. 2020; El-Beltagi
et al. 2020), and sulfur (Maillard et al. 2018; Réthoré et al. 2020). The interaction of
silicon with the above-mentioned nutrient elements has not been explored extensively and further investigation in this direction is highly recommended.
2.4.6 UV-B Radiation Stress
Apart from the above-mentioned stresses, UV-B stress is considered as harmful
stress for both plants and animals including humans (Jordan 2002; Yin and Ulm
2017; Chakraborty et al. 2017). The reason lies in its ability to influence biochemistry, physiology, and genetic changes in plants (Jordan 2002; Tripathi et al. 2017;
Etesami and Jeong 2018; Azarafshan et al. 2020). The exogenous application of
silicon to the plants has also resulted in alleviating the effects of UV-B stress on
many plants (Fang et al. 2011; Yao et al. 2011; Schaller et al. 2013; Tripathi et al.
2017). All these studies together in combination have revealed that the exogenous
application of silicon results in the formation of a cuticle–Si double layer, which acts
as a glass layer and reduces the further transmission of UV radiation from the
epidermis (Gatto et al. 1998; Currie and Perry 2007; Etesami and Jeong 2018). In
addition, the silicon application induces resistance in plants by modifying ROS
consumption (Shen et al. 2010), levels of UV absorbing compounds (Liang et al.
2015), and antioxidative enzyme activities (Fang et al. 2019).
2.4.7 Wounding Stress
One of the interesting stresses among the variety of non-biological stresses is
wounding stress that results in physical injury in the plants (Malhotra and Kapoor
2019). This arises actually from strong winds or water and due to the attack by
herbivores (insects, birds, and nematodes) (Malhotra and Kapoor 2019; Singh et al.
2020; Souri et al. 2020). Primarily, these physical injuries increase the vulnerability
to pathogenic attack by creating openings in plant organs as well as initiate oxidative
stress at the secondary level that ultimately leads to death in serious cases via cell
apoptosis (Malhotra and Kapoor 2019). In order to cope-up with wounding stress,
the silicon treatment results in modulation in the levels of antioxidant enzymes (such
2 Silicon: A Plant Nutritional “Non-Entity” for Mitigating Abiotic
31
conditions as well as toxicity; for example, calcium (Mali and Aery 2008; Etesami
and Jeong 2018; Dong et al. 2018; do Nascimento et al. 2020), magnesium (Hosseini
et al. 2019; do Nascimento et al. 2020), boron (Savić and Marjanović-Jeromela
2013; Liu et al. 2017; Metwally et al. 2018; Pereira de Souza Junior et al. 2019;
Oliveira et al. 2020), iron (You-Qiang et al. 2012; Pavlovic et al. 2013; Bityutskii
et al. 2014; Patil et al. 2018; do Nascimento et al. 2020; dos Santos et al. 2020),
manganese (Dragišić Maksimović et al. 2007; Patil et al. 2018; de Oliveira et al.
2019; do Nascimento et al. 2020), zinc (Gu et al. 2012; Bityutskii et al. 2014;
Hernandez-Apaolaza 2014; Pascual et al. 2016; do Nascimento et al. 2020; Raj
et al. 2020), copper (Frantz et al. 2011; Patil et al. 2018; Raj et al. 2020; El-Beltagi
et al. 2020), and sulfur (Maillard et al. 2018; Réthoré et al. 2020). The interaction of
silicon with the above-mentioned nutrient elements has not been explored extensively and further investigation in this direction is highly recommended.
2.4.6 UV-B Radiation Stress
Apart from the above-mentioned stresses, UV-B stress is considered as harmful
stress for both plants and animals including humans (Jordan 2002; Yin and Ulm
2017; Chakraborty et al. 2017). The reason lies in its ability to influence biochemistry, physiology, and genetic changes in plants (Jordan 2002; Tripathi et al. 2017;
Etesami and Jeong 2018; Azarafshan et al. 2020). The exogenous application of
silicon to the plants has also resulted in alleviating the effects of UV-B stress on
many plants (Fang et al. 2011; Yao et al. 2011; Schaller et al. 2013; Tripathi et al.
2017). All these studies together in combination have revealed that the exogenous
application of silicon results in the formation of a cuticle–Si double layer, which acts
as a glass layer and reduces the further transmission of UV radiation from the
epidermis (Gatto et al. 1998; Currie and Perry 2007; Etesami and Jeong 2018). In
addition, the silicon application induces resistance in plants by modifying ROS
consumption (Shen et al. 2010), levels of UV absorbing compounds (Liang et al.
2015), and antioxidative enzyme activities (Fang et al. 2019).
2.4.7 Wounding Stress
One of the interesting stresses among the variety of non-biological stresses is
wounding stress that results in physical injury in the plants (Malhotra and Kapoor
2019). This arises actually from strong winds or water and due to the attack by
herbivores (insects, birds, and nematodes) (Malhotra and Kapoor 2019; Singh et al.
2020; Souri et al. 2020). Primarily, these physical injuries increase the vulnerability
to pathogenic attack by creating openings in plant organs as well as initiate oxidative
stress at the secondary level that ultimately leads to death in serious cases via cell
apoptosis (Malhotra and Kapoor 2019). In order to cope-up with wounding stress,
the silicon treatment results in modulation in the levels of antioxidant enzymes (such
2 Silicon: A Plant Nutritional “Non-Entity” for Mitigating Abiotic
31