16.6 Ca
2+ -Mediated Local and Systemic Signalling During
Herbivory
Ca
2+ ions travel a long distance from the place of wounding on plasma membrane to
nucleus via many transporters and sensors. As Ca
2+ signals convey the signal it
converts into the systematic defence mechanism to counterattack the herbivoryrelated injury. Ca
2+ -transporter and sensor maintains the spiking and oscillation,
i.e. Ca
2+ signature to confer accurate message. There is an integrative “crosstalk”
that happens between the induced plant defence against herbivore and the signalling
molecules initiated by Ca
2+ , followed by activation of reactive oxygen species
(H 2 O 2 ), protein kinases (MAPKs), jasmonic acid, salicylic acid, ethylene,
oxophytodienoic acid, and other obscure members of the octadecanoid family
(Maffei et al. 2007a, b; Mithöfer et al. 2018). Ca
2+ ions trigger the accumulation
of JA (Yan et al. 2018). GLCRs channels regulate Ca
2+ for rapid systematic
induction of JA against herbivore wounding (Mousavi et al. 2013). The Ca
2+ kinetics
conveyances downstream by interacting with sensor relay proteins with targeted
proteins. These proteins initiate gene expression and activate direct and indirect
defence. These proteins also influence ionic changes via other membrane
transporters by activating transcriptional factors. The molecular mechanisms arbitrate by Ca
2+ responsive gene expression is still concealed. The reason behind this
ambiguity is unable to distinguish between Ca
2+ -dependent stress response and Ca
2
+
-independent stress response. A study conducted using antagonists of CaM-WP7
and SKF-7171, revealed that only ~3.3% (out of 230 genes) of Arabidopsis genes
are Ca
2+ regulated and most of them were induced during early time points of stress.
Recent experimental studies suggested that besides secondary phytometabolites,
mobile plant hormones such as auxin and cytokinin were also involved in plant
defense against herbivore. When wounding is caused in Nicotiana attenuata,
caffeoylputrescine accumulated in leaves due to mutation in the homologs of
cytokinin receptor CHASE-DOMAIN CONTAINING HIS KINASE 2 (Schäfer
et al. 2015). A plant produces many specialized peculiar secondary metabolites
which function as defence against herbivores. Ca
2+ induces ROS production for
transmission of damaging signal to nearby cells (Gilroy et al. 2016).
16.7 Conclusion
Plants perceive and respond to insect attack by activating defence responses through
activation of early signalling components. One of the most important early signalling
events is Ca
2+ signalling. During herbivory, due to membrane depolarization, an
elevated level of Ca
2+ is observed within seconds to minutes, which serves as a
signal. Further, different types of Ca
2+ -binding proteins that are part of a larger
regulatory network identify this signal and decode [Ca
2+ ] cyt elevation after
wounding/feeding. This relay of signal by Ca
2+ relayers and Ca
2+ responders reaches
to nucleus and specific defence reprogramming proceeds via signalling networks
that include phytohormones, secondary metabolites, and transcription factors,
16 Role of Calcium Signalling During Plant–Herbivore Interaction
503
2+ -Mediated Local and Systemic Signalling During
Herbivory
Ca
2+ ions travel a long distance from the place of wounding on plasma membrane to
nucleus via many transporters and sensors. As Ca
2+ signals convey the signal it
converts into the systematic defence mechanism to counterattack the herbivoryrelated injury. Ca
2+ -transporter and sensor maintains the spiking and oscillation,
i.e. Ca
2+ signature to confer accurate message. There is an integrative “crosstalk”
that happens between the induced plant defence against herbivore and the signalling
molecules initiated by Ca
2+ , followed by activation of reactive oxygen species
(H 2 O 2 ), protein kinases (MAPKs), jasmonic acid, salicylic acid, ethylene,
oxophytodienoic acid, and other obscure members of the octadecanoid family
(Maffei et al. 2007a, b; Mithöfer et al. 2018). Ca
2+ ions trigger the accumulation
of JA (Yan et al. 2018). GLCRs channels regulate Ca
2+ for rapid systematic
induction of JA against herbivore wounding (Mousavi et al. 2013). The Ca
2+ kinetics
conveyances downstream by interacting with sensor relay proteins with targeted
proteins. These proteins initiate gene expression and activate direct and indirect
defence. These proteins also influence ionic changes via other membrane
transporters by activating transcriptional factors. The molecular mechanisms arbitrate by Ca
2+ responsive gene expression is still concealed. The reason behind this
ambiguity is unable to distinguish between Ca
2+ -dependent stress response and Ca
2
+
-independent stress response. A study conducted using antagonists of CaM-WP7
and SKF-7171, revealed that only ~3.3% (out of 230 genes) of Arabidopsis genes
are Ca
2+ regulated and most of them were induced during early time points of stress.
Recent experimental studies suggested that besides secondary phytometabolites,
mobile plant hormones such as auxin and cytokinin were also involved in plant
defense against herbivore. When wounding is caused in Nicotiana attenuata,
caffeoylputrescine accumulated in leaves due to mutation in the homologs of
cytokinin receptor CHASE-DOMAIN CONTAINING HIS KINASE 2 (Schäfer
et al. 2015). A plant produces many specialized peculiar secondary metabolites
which function as defence against herbivores. Ca
2+ induces ROS production for
transmission of damaging signal to nearby cells (Gilroy et al. 2016).
16.7 Conclusion
Plants perceive and respond to insect attack by activating defence responses through
activation of early signalling components. One of the most important early signalling
events is Ca
2+ signalling. During herbivory, due to membrane depolarization, an
elevated level of Ca
2+ is observed within seconds to minutes, which serves as a
signal. Further, different types of Ca
2+ -binding proteins that are part of a larger
regulatory network identify this signal and decode [Ca
2+ ] cyt elevation after
wounding/feeding. This relay of signal by Ca
2+ relayers and Ca
2+ responders reaches
to nucleus and specific defence reprogramming proceeds via signalling networks
that include phytohormones, secondary metabolites, and transcription factors,
16 Role of Calcium Signalling During Plant–Herbivore Interaction
503