silicon (Liang et al. 2003). Electrolyte leakage is an important indicator of thermal
stress in plants. Si-supplementation causes reduced electrolyte leakage due to high
temperature (Ma et al. 2015). Thus, Si may have a role in generating thermal stability
in cell membranes although further investigations need to be carried out to decipher
the mechanisms and pathways involved.
In congruence with heat stress, chilling temperature conditions limit the growth
and development of plants drastically, by diminishing root proliferation and early
plant growth (Moradtalab et al. 2018). Cold stress and tolerance studies have been
extensively studied using maize as a model plant. Chilling stress results in chlorosis,
necrosis of leaf tissue, and inhibits root and shoot extension growth (Imran et al.
2013). These morphological deviations are often accompanied by physiological
stress responses such as elevated production of ROS (Pei et al. 2010). Mechanisms
involved in mitigating chilling stress still remain unexplored. Recent studies reveal
that cold stress amelioration is often carried out by Zn, Mn, and Si, commonly
known as the “cold stress protectants” (Bradáčová et al. 2016). Si helps to translocate
micronutrients of seed reserved to seedlings under cold stress (Moradtalab et al.
2018). Silicon has the ability to prevent leaching due to cold stress by maintaining
Zn/Mn reserves in the seed, which also act as cold stress suppressants. The most
significant role of Si in mitigating cold stress is the restoration of root growth in
maize plants. A similar role of Si under cold stress has been noted in soybean plants
as well (Pascual et al. 2016).
Recent studies have shed some light on the existence of the ICE–CBF–COR
pathway, which plays a key role in imparting cold stress acclimatization (Ritonga
and Chen 2020). Activation of C-binding repeats (CBF) via cold induction by the
inducer CBF-expression (ICE) results in the activation of cold responsive genes.
Activation and regulation of the ICE–CBF–COR pathway result in the expression of
several downstream genes, necessary for imparting tolerance against cold and
chilling environmental conditions (Ritonga and Chen 2020). Low-temperature stress
can often be categorized into chilling stress (<20
C) and freezing stress (<0
C)
(Mickelbart et al. 2015; Guo et al. 2017; Liu and Zhou 2018; Shi et al. 2018). Crops
such as tomato, soybean, cotton, corn, rice, and potato are intolerant to cold
environmental conditions (both chilling and freezing stress). However, plants like
oats, barley, rye, and wheat show good adaptability to cold stress (Zhang et al. 2011,
2017). Under low-temperature stress conditions, ICE mediated regulation of
Gibberellic acid (GA) level is essential for cold tolerance. Plants facing cold stress
have to maintain the stability of cell membranes and structural integrity for survival
(Chen et al. 2018). Exposure to freezing conditions can often lead to the formation of
ice nucleators and crystals in plant cell apoplast which ultimately results in dehydration, electrolyte leakage, and membrane disintegration (Puhakainen 2004). Under
extreme situations, these ice crystals can puncture the cell leading to plants death
(Demidchik et al. 2014; Sun et al. 2019). The most commonly observed mechanism
for studying cold temperature tolerance is the accumulation of cryoprotective
polypeptides, sugars, and osmolytes (Khan et al. 2015).
Furthermore, application of silicon to leaves of barley under cold (chilling as well
as freezing stress) leads to an increase in levels of antioxidant enzymes, soluble
2 Silicon: A Plant Nutritional “Non-Entity” for Mitigating Abiotic
29
stress in plants. Si-supplementation causes reduced electrolyte leakage due to high
temperature (Ma et al. 2015). Thus, Si may have a role in generating thermal stability
in cell membranes although further investigations need to be carried out to decipher
the mechanisms and pathways involved.
In congruence with heat stress, chilling temperature conditions limit the growth
and development of plants drastically, by diminishing root proliferation and early
plant growth (Moradtalab et al. 2018). Cold stress and tolerance studies have been
extensively studied using maize as a model plant. Chilling stress results in chlorosis,
necrosis of leaf tissue, and inhibits root and shoot extension growth (Imran et al.
2013). These morphological deviations are often accompanied by physiological
stress responses such as elevated production of ROS (Pei et al. 2010). Mechanisms
involved in mitigating chilling stress still remain unexplored. Recent studies reveal
that cold stress amelioration is often carried out by Zn, Mn, and Si, commonly
known as the “cold stress protectants” (Bradáčová et al. 2016). Si helps to translocate
micronutrients of seed reserved to seedlings under cold stress (Moradtalab et al.
2018). Silicon has the ability to prevent leaching due to cold stress by maintaining
Zn/Mn reserves in the seed, which also act as cold stress suppressants. The most
significant role of Si in mitigating cold stress is the restoration of root growth in
maize plants. A similar role of Si under cold stress has been noted in soybean plants
as well (Pascual et al. 2016).
Recent studies have shed some light on the existence of the ICE–CBF–COR
pathway, which plays a key role in imparting cold stress acclimatization (Ritonga
and Chen 2020). Activation of C-binding repeats (CBF) via cold induction by the
inducer CBF-expression (ICE) results in the activation of cold responsive genes.
Activation and regulation of the ICE–CBF–COR pathway result in the expression of
several downstream genes, necessary for imparting tolerance against cold and
chilling environmental conditions (Ritonga and Chen 2020). Low-temperature stress
can often be categorized into chilling stress (<20
C) and freezing stress (<0
C)
(Mickelbart et al. 2015; Guo et al. 2017; Liu and Zhou 2018; Shi et al. 2018). Crops
such as tomato, soybean, cotton, corn, rice, and potato are intolerant to cold
environmental conditions (both chilling and freezing stress). However, plants like
oats, barley, rye, and wheat show good adaptability to cold stress (Zhang et al. 2011,
2017). Under low-temperature stress conditions, ICE mediated regulation of
Gibberellic acid (GA) level is essential for cold tolerance. Plants facing cold stress
have to maintain the stability of cell membranes and structural integrity for survival
(Chen et al. 2018). Exposure to freezing conditions can often lead to the formation of
ice nucleators and crystals in plant cell apoplast which ultimately results in dehydration, electrolyte leakage, and membrane disintegration (Puhakainen 2004). Under
extreme situations, these ice crystals can puncture the cell leading to plants death
(Demidchik et al. 2014; Sun et al. 2019). The most commonly observed mechanism
for studying cold temperature tolerance is the accumulation of cryoprotective
polypeptides, sugars, and osmolytes (Khan et al. 2015).
Furthermore, application of silicon to leaves of barley under cold (chilling as well
as freezing stress) leads to an increase in levels of antioxidant enzymes, soluble
2 Silicon: A Plant Nutritional “Non-Entity” for Mitigating Abiotic
29