3.4 Acoustic and electric signals
Plants utilize acoustic and electric signals as internal and inter-plant
signals. A sound vibration signal can be generated by a herbivore
walking on the plant, breaking trichomes, chewing the plant, and even by
water stress (Caicedo-Lopez, Contreras-Medina, Guevara-Gonzaleza,
Perez-Matzumotob & Ruiz-Ruedab, 2020, Kollasch, Abdul‑Kaf, Body, Pinto,
Appel & Cocroft, 2020). Pest species might be discriminated based on
the vibration frequency they produce (Kollasch et al. , 2020).
Perception of a sound vibration signal modifies plant epigenetics,
transcriptome, proteome, and metabolome (Ghosh, Mishra, Choi, Kwon, Won
Bae, Park & Bae, 2016, Jung, Kim, Jung, Jeong & Ryu, 2020). Sound
vibration signal perception modulates defense hormones such as SA,
leading to activation of MAPKs, MYBs, and transcription factors (Body,
Neer, C., Lin, Vu & Cocroft, 2019, Ghosh et al. , 2016). This
upregulation of key enzymes and secondary metabolites, including
catalase and PAL, increases the biosynthesis of phenols, alkaloids,
terpenes, and oxylipin-derivative volatile organic compounds (VOCs)
(Body et al. , 2019, Ghosh et al. , 2016, Kollasch et
al. , 2020). These metabolites enhance plant resistance or act as
signals in plant–plant communication. Jung et al. (2020)
reported that sound vibration induces resistance against the root
pathogen Ralstonia solanacearum by modulating cytokinin
signaling, increasing aliphatic glucosinolate biosynthesis through
epigenetic DNA methylation by H3K27me3, and improving cell wall
reinforcement by downregulating miR397b suppression of lignin
accumulation–related transcripts. Vibration sensing is an
evolutionarily ancient system that arose before vascular plants emerged,
as microalga also have mechanosensory proteins that respond to vibration
(Paika, Jinb, Simc & N.L., 2018).
Electric signals, primarily Ca2+ signaling, have
important roles in intra- and inter-plant signaling (Choi, Miller,
Wallace, Harper, Mittler & Gilroy, 2017, de Toledo, Parise, Simmi,
Costa, Senko, Debono & Souza, 2019, Simmi, Dallagnol, Ferreira, Pereira
& Souza, 2020). The oomycete pathogen Pythium aphanidermatumexploits electric signals to target host roots (Van West, Morris, Reid,
Appiah, Osborne, Campbell, Shepherd & Gow, 2002). Both acoustic and
electric signals have high transmission speed and good potential for use
in precision agriculture (Choi et al. , 2017, Kollasch et
al. , 2020).