16.3.2 Ca
2+ /Proton Exchangers
The Ca
2+ /H
+ is an antiporter channel, simultaneously transports the Ca
2+ and H
+
antagonistically to each side of plasma membrane. The driven energy for antiporter
is proton motive force (PMF) (Sanders et al. 2002). Ca
2+ /H
+ antiporters have less
affinity for Ca
2+ than Ca
2+ -ATPases. This antiporter is also known as cation
exchanger (CAX) because of their function. CAX1 and CAX3 have high specificity
for Ca
2+ binding and maintenance of Ca
2+ homeostasis than any other CAX.
External supply of Ca
2+ increases the expression of CAX1 and CAX3. CAX1
expressed in shoot, whereas CAX3 expressed in roots strongly (Cheng et al.
2003). This indicates that CAX1 is responsible for manoeuvre of above-ground
stresses and CAX3 controls underground stresses. CAX proteins are expressed
during abiotic stresses such as heavy metal, drought, and salinity stress (Zhang
et al. 2008). Role of CAX during herbivore stress is still unknown and yet to be
discovered.
16.3.3 Ca
2+ Channels
The transportation of Ca
2+ into the cytosol occurs during the various stages of
simulation. The Ca
2+ ions are transported via depolarized activated Ca
2+ channels,
hyperpolarized activated Ca
2+ channels, voltage-dependent channels, voltageindependent channels, and ligated gated channels (Sanders et al. 2002). Subcellular
organelles have also Ca
2+ channels and they also participate in signal transduction.
Voltage-dependent and ligate gated channels are localized in subcellular organelles,
membranes of vacuoles, and endoplasmic reticulum (Sanders et al. 2002; Demidchik
and Maathuis 2007). The channels are stimulated either by phytohormone such as
abscisic acid, jasmonic acid or by ROS like H 2 O 2 . Other types of channels include
cyclic nucleotide-gated channels, glutamate receptor-like, two-pore channels, and
annexins (Dodd et al. 2010).
16.3.4 Cyclic Nucleotide: Gated Channels (CNGCs)
In plants cyclic nucleotide-gated channels (CNGCs) have crucial role in Ca
2+
translocation in plant cells (Leng et al. 1999; Urquhart et al. 2007). CNGCs include
6 trans-membrane and a pore domain. Trans-membrane domains assemble
tetramerically for the formation of pore and are localized to the plasma membrane
(K Jha et al. 2016). They are permeable to monovalent ions and Ca
2+ ions when
expressed heterologously. With cyclic nucleotide-binding domain, CNGCs are also
able to react to calmodulin sensors (Romeis and Herde 2014; Schuurink et al. 1998).
This property helps in transduction of Ca
2+ signal cascade during herbivore attack
(Meena and Vadassery 2015; Breeze 2019). The role of one of the Ca
2+ CNGC,
CNGC 19 has been implicated in Arabidopsis defence signalling against Spodoptera
496
A. Kumar et al.
2+ /Proton Exchangers
The Ca
2+ /H
+ is an antiporter channel, simultaneously transports the Ca
2+ and H
+
antagonistically to each side of plasma membrane. The driven energy for antiporter
is proton motive force (PMF) (Sanders et al. 2002). Ca
2+ /H
+ antiporters have less
affinity for Ca
2+ than Ca
2+ -ATPases. This antiporter is also known as cation
exchanger (CAX) because of their function. CAX1 and CAX3 have high specificity
for Ca
2+ binding and maintenance of Ca
2+ homeostasis than any other CAX.
External supply of Ca
2+ increases the expression of CAX1 and CAX3. CAX1
expressed in shoot, whereas CAX3 expressed in roots strongly (Cheng et al.
2003). This indicates that CAX1 is responsible for manoeuvre of above-ground
stresses and CAX3 controls underground stresses. CAX proteins are expressed
during abiotic stresses such as heavy metal, drought, and salinity stress (Zhang
et al. 2008). Role of CAX during herbivore stress is still unknown and yet to be
discovered.
16.3.3 Ca
2+ Channels
The transportation of Ca
2+ into the cytosol occurs during the various stages of
simulation. The Ca
2+ ions are transported via depolarized activated Ca
2+ channels,
hyperpolarized activated Ca
2+ channels, voltage-dependent channels, voltageindependent channels, and ligated gated channels (Sanders et al. 2002). Subcellular
organelles have also Ca
2+ channels and they also participate in signal transduction.
Voltage-dependent and ligate gated channels are localized in subcellular organelles,
membranes of vacuoles, and endoplasmic reticulum (Sanders et al. 2002; Demidchik
and Maathuis 2007). The channels are stimulated either by phytohormone such as
abscisic acid, jasmonic acid or by ROS like H 2 O 2 . Other types of channels include
cyclic nucleotide-gated channels, glutamate receptor-like, two-pore channels, and
annexins (Dodd et al. 2010).
16.3.4 Cyclic Nucleotide: Gated Channels (CNGCs)
In plants cyclic nucleotide-gated channels (CNGCs) have crucial role in Ca
2+
translocation in plant cells (Leng et al. 1999; Urquhart et al. 2007). CNGCs include
6 trans-membrane and a pore domain. Trans-membrane domains assemble
tetramerically for the formation of pore and are localized to the plasma membrane
(K Jha et al. 2016). They are permeable to monovalent ions and Ca
2+ ions when
expressed heterologously. With cyclic nucleotide-binding domain, CNGCs are also
able to react to calmodulin sensors (Romeis and Herde 2014; Schuurink et al. 1998).
This property helps in transduction of Ca
2+ signal cascade during herbivore attack
(Meena and Vadassery 2015; Breeze 2019). The role of one of the Ca
2+ CNGC,
CNGC 19 has been implicated in Arabidopsis defence signalling against Spodoptera
496
A. Kumar et al.