Moreover, Si-supplementation also enhances transpirational bypassing of toxic ions
from symplast streamflow (Coskun et al. 2016). This theory allows to propose that
the movement of Na
+ and Cl
À is limited in rice plants by suberized exodermis and
endodermis of roots, thereby bypassing the step of xylem loading via symplast
(Coskun et al. 2016). Much like in salinity stress, foliar supplementation of Si brings
about an increase in the expression of different aquaporins (AQPs) located in the
membranes of root cells.
2.4.2 Salinity Stress
About 20% of global crop production is affected by salinity stress (Hussain et al.
2018). Under salt stress, rice plants display an interesting deviation in the apoplastic
movement of noxious Na
+ and Cl
À
, on exposure to Si (Shi et al. 2013). Si-mediated
amelioration of salt stress has been studied and deciphered at various biochemical
and physiological levels. Starting from its impact on roots, the primary site of ion
uptake to serial tissue like leaves wherein salt stress has a drastic effect on several
proteins and enzymes related to photosynthesis and stomatal opening (Liu et al.
2019; Gogna and Bhatla 2019, 2020). Silicon protects photosynthetic machinery of
plants under stress due to persisting soil salinity by preventing pigment degradation
and regulation of several photosystems and chloroplast-related proteins (Muneer
et al. 2014; Soundararajan et al. 2017). Exogenous application of Si modulates
enzymatic antioxidant machinery constituting enzymes like catalase, superoxide
dismutase, and guaiacol/ascorbate peroxidase (Zhu et al. 2004; Manivannan et al.
2015). The primary action undertaken by a stressed plant to overcome salinity is the
restriction of Na
+
/Cl
À uptake via roots (Liu et al. 2019; Gogna et al. 2020). Exogenously supplied Si not only limits the uptake of toxic ions by plant roots but also
regulates several other essential biochemical aspects like photosynthesis, maintenance of redox equilibrium, and effective distribution of nutrients to the plant (Liu
et al. 2019). Similar to Ca
2+ , the application of Si not only restricts excess uptake of
Na
+ but also mediates accumulation of K
+
, thereby impacting tolerance against
salinity. This study has been extensively carried out across sugarcane, aloe, zinnia,
and rose (Ashraf et al. 2010; Manivannan et al. 2015; Garg and Bhandari 2016;
Soundararajan et al. 2018). The foremost role of Si in alleviating salt stress is its
possible interaction with noxious ions responsible for oxidative stress and disrupted
ionic homeostasis. K
+ is the most essential element necessary for plant growth,
development, and yield. However, uptake of Na
+ under salt stress often results in K
+
deficiency (Liebersbach et al. 2004). Thus, the addition of Si not only negates the
competition between Na
+ and K
+ but also alleviates K
+ distribution in salt-stressed
wheat and blueberry (Tuna et al. 2008).
Plant root aquaporins are involved in the facilitation of water and mineral
nutrition transportation (Liu et al. 2019). NIP family of AQPs has been found to
play a significant role in the uptake and transport of Si and other metalloids (Wu and
Beitz 2007). Studies pertaining to rice plants have revealed that efflux and influx of
Si are carried out via the NIP family of AQPs (Ma et al. 2006). Apart from NIPs,
2 Silicon: A Plant Nutritional “Non-Entity” for Mitigating Abiotic
25
from symplast streamflow (Coskun et al. 2016). This theory allows to propose that
the movement of Na
+ and Cl
À is limited in rice plants by suberized exodermis and
endodermis of roots, thereby bypassing the step of xylem loading via symplast
(Coskun et al. 2016). Much like in salinity stress, foliar supplementation of Si brings
about an increase in the expression of different aquaporins (AQPs) located in the
membranes of root cells.
2.4.2 Salinity Stress
About 20% of global crop production is affected by salinity stress (Hussain et al.
2018). Under salt stress, rice plants display an interesting deviation in the apoplastic
movement of noxious Na
+ and Cl
À
, on exposure to Si (Shi et al. 2013). Si-mediated
amelioration of salt stress has been studied and deciphered at various biochemical
and physiological levels. Starting from its impact on roots, the primary site of ion
uptake to serial tissue like leaves wherein salt stress has a drastic effect on several
proteins and enzymes related to photosynthesis and stomatal opening (Liu et al.
2019; Gogna and Bhatla 2019, 2020). Silicon protects photosynthetic machinery of
plants under stress due to persisting soil salinity by preventing pigment degradation
and regulation of several photosystems and chloroplast-related proteins (Muneer
et al. 2014; Soundararajan et al. 2017). Exogenous application of Si modulates
enzymatic antioxidant machinery constituting enzymes like catalase, superoxide
dismutase, and guaiacol/ascorbate peroxidase (Zhu et al. 2004; Manivannan et al.
2015). The primary action undertaken by a stressed plant to overcome salinity is the
restriction of Na
+
/Cl
À uptake via roots (Liu et al. 2019; Gogna et al. 2020). Exogenously supplied Si not only limits the uptake of toxic ions by plant roots but also
regulates several other essential biochemical aspects like photosynthesis, maintenance of redox equilibrium, and effective distribution of nutrients to the plant (Liu
et al. 2019). Similar to Ca
2+ , the application of Si not only restricts excess uptake of
Na
+ but also mediates accumulation of K
+
, thereby impacting tolerance against
salinity. This study has been extensively carried out across sugarcane, aloe, zinnia,
and rose (Ashraf et al. 2010; Manivannan et al. 2015; Garg and Bhandari 2016;
Soundararajan et al. 2018). The foremost role of Si in alleviating salt stress is its
possible interaction with noxious ions responsible for oxidative stress and disrupted
ionic homeostasis. K
+ is the most essential element necessary for plant growth,
development, and yield. However, uptake of Na
+ under salt stress often results in K
+
deficiency (Liebersbach et al. 2004). Thus, the addition of Si not only negates the
competition between Na
+ and K
+ but also alleviates K
+ distribution in salt-stressed
wheat and blueberry (Tuna et al. 2008).
Plant root aquaporins are involved in the facilitation of water and mineral
nutrition transportation (Liu et al. 2019). NIP family of AQPs has been found to
play a significant role in the uptake and transport of Si and other metalloids (Wu and
Beitz 2007). Studies pertaining to rice plants have revealed that efflux and influx of
Si are carried out via the NIP family of AQPs (Ma et al. 2006). Apart from NIPs,
2 Silicon: A Plant Nutritional “Non-Entity” for Mitigating Abiotic
25