16.3 Calcium: Transporters During Plant–Herbivore Attack
Survival and fitness of plants during any environmental stress depends on the
quickness of recognition of the “enemy” and induction of effective response against
the prevailing situation. For any quick response, channels/transporters of a signal
have significant contribution on transportation of ions (Erb and Reymond 2019). As
soon as herbivory is perceived by the plant cell, transportation of Ca
2+ ions takes
place into the cytosol and other subcellular compartments through channels (White
2000). To restore normal condition in cells, channels efflux the ions to create
concentration gradient and ready for perceiving next signal. Electrophysiological
studies suggested variety of Ca
2+ ion transporters are present in the cell that are
localized in the plasma membrane and membrane of subcellular organelles (Schiøtt
et al. 2004; Urquhart et al. 2007). Their mode of activation is also different like
voltage based, voltage insensitive, and membrane polarization based. Different Ca
2+
transporters have varied affinity towards ions so they work according to the situation.
Binding affinity of Ca
2+ -ATPases is high (K m ¼ 1–10 mM) but it has low capacity
for transportation, maintains cellular Ca
2+ homeostasis in cytosol. Whereas, Ca
2+ /H
+
antiporter has low affinity of binding (K m ¼ 10–15 mM), but it quickly transports
ions and are active during signal perception (Hirschi 2001).
16.3.1 Ca
2+ -ATPases
Different Ca
2+ -ATPases are involved in active Ca
2+ transportation and maintenance
of Ca
2+ homeostasis in cytosol (Bose et al. 2011; Maffei et al. 2007a, b). The
ATP-dependent P-type ATPases (ADPA) are one of them delivering the Ca
2+ ions
across the plasma membrane. The integrants of signalling pathway activates transient of ADPA. In Arabidopsis, two clades of ATP-dependent P-type ATPases,
P-type ATPase II A and P-type ATPase II B were studied (Sanders et al. 2002). The
P-type ATPase II A (ECA) is present in endoplasmic reticulum, whereas P-type
ATPase II B (ACA) functions as an autoinhibitory function (Boursiac and Harper
2007). ECA is a broad nucleotide specific ATPase. In ACA, calmodulin-binding
domain is present. In Arabidopsis, isoforms of ACA are localized in different
subcellular membranes in plasma membrane, vacuolar membrane, and plastid membrane. This indicates that ACA has the capabilities for transducing Ca
2+ signals
during various stresses (Sarwat and Tuteja 2007). On pathogen attack transcripts of
ACA12 and ACA13 are highly upregulated (Boursiac and Harper 2007). ACA of
different membrane has different calmodulin-binding affinities and activity. Upon
insect attack a temporary complex calmodulin-Ca
2+ is formed, which institutes
signal transfer (Huda et al. 2013). Upon insect attack, the initial Ca
2+ burst is
followed by a consistent decrease in the (Ca
2+ ) cyt , which implies the involvement
of a Ca
2+ efflux-mediated, increased Ca
2+ -ATPase activity (Maffei et al. 2007a, b).
16 Role of Calcium Signalling During Plant–Herbivore Interaction
495
Survival and fitness of plants during any environmental stress depends on the
quickness of recognition of the “enemy” and induction of effective response against
the prevailing situation. For any quick response, channels/transporters of a signal
have significant contribution on transportation of ions (Erb and Reymond 2019). As
soon as herbivory is perceived by the plant cell, transportation of Ca
2+ ions takes
place into the cytosol and other subcellular compartments through channels (White
2000). To restore normal condition in cells, channels efflux the ions to create
concentration gradient and ready for perceiving next signal. Electrophysiological
studies suggested variety of Ca
2+ ion transporters are present in the cell that are
localized in the plasma membrane and membrane of subcellular organelles (Schiøtt
et al. 2004; Urquhart et al. 2007). Their mode of activation is also different like
voltage based, voltage insensitive, and membrane polarization based. Different Ca
2+
transporters have varied affinity towards ions so they work according to the situation.
Binding affinity of Ca
2+ -ATPases is high (K m ¼ 1–10 mM) but it has low capacity
for transportation, maintains cellular Ca
2+ homeostasis in cytosol. Whereas, Ca
2+ /H
+
antiporter has low affinity of binding (K m ¼ 10–15 mM), but it quickly transports
ions and are active during signal perception (Hirschi 2001).
16.3.1 Ca
2+ -ATPases
Different Ca
2+ -ATPases are involved in active Ca
2+ transportation and maintenance
of Ca
2+ homeostasis in cytosol (Bose et al. 2011; Maffei et al. 2007a, b). The
ATP-dependent P-type ATPases (ADPA) are one of them delivering the Ca
2+ ions
across the plasma membrane. The integrants of signalling pathway activates transient of ADPA. In Arabidopsis, two clades of ATP-dependent P-type ATPases,
P-type ATPase II A and P-type ATPase II B were studied (Sanders et al. 2002). The
P-type ATPase II A (ECA) is present in endoplasmic reticulum, whereas P-type
ATPase II B (ACA) functions as an autoinhibitory function (Boursiac and Harper
2007). ECA is a broad nucleotide specific ATPase. In ACA, calmodulin-binding
domain is present. In Arabidopsis, isoforms of ACA are localized in different
subcellular membranes in plasma membrane, vacuolar membrane, and plastid membrane. This indicates that ACA has the capabilities for transducing Ca
2+ signals
during various stresses (Sarwat and Tuteja 2007). On pathogen attack transcripts of
ACA12 and ACA13 are highly upregulated (Boursiac and Harper 2007). ACA of
different membrane has different calmodulin-binding affinities and activity. Upon
insect attack a temporary complex calmodulin-Ca
2+ is formed, which institutes
signal transfer (Huda et al. 2013). Upon insect attack, the initial Ca
2+ burst is
followed by a consistent decrease in the (Ca
2+ ) cyt , which implies the involvement
of a Ca
2+ efflux-mediated, increased Ca
2+ -ATPase activity (Maffei et al. 2007a, b).
16 Role of Calcium Signalling During Plant–Herbivore Interaction
495