3.2 Wireless signal transfer
Plant infochemicals can diffuse around the elicited plant (producer),
and are amplified by receiver plants to expand their effective zone.
Infochemicals can diffuse distances of a few centimeters to several
meters according to their chemical structure and vectors such as
mycorrhiza and dodder. Wheat infected by Fusarium culmorumtransfers signals to neighbor plants located 1–3 meters distant.
However, there is a negative correlation between distance and response
intensity in the receiver plant. Several studies show that receiver
plants also propagate signals and act as nodes in inter-plant signaling
(Chen, Yang, Chen, Luo, Cui, Yan & Gerwick, 2019a, Piesik, Pańka,
Jeske, Wenda-Piesik, Delaney & Weaver, 2013, Wenig et al. ,
2019). Thus, neighboring plants amplify signals in clusters of receiver
plants. However, the regulation of induced signaling pathways involved
in infochemical synthesis in receiver plants requires time, which
results in a wave of infochemical synthesis and metabolic responses in
receiver plants. Falik, Mordoch, Ben-Natan, Vanunu, Goldstein and
Novoplansky (2012) observed that osmotic stress in Pisum sativumactivated stomatal closure in the focal plant and the next three plants
in the cluster within 1 h, whereas more distant plants responded after 1
h. In this study, focal plant stomata remained closed for 24 h, whereas
receiver plants opened their stomatal apertures because they did not
directly encounter osmotic stress. Receiver plants did prepare for
imminent osmotic stress, with the ability to return to a naive state if
the stress was resolved. Weed plants use stress signals from P.
sativum neighbors to improve their acclimation (Falik et al. ,
2012).
Wenig et al. (2019) showed that monoterpenes such as α- and
β-pinene act as immunity-inducing signals between plants (Figure 3).
Systemic acquired resistance (SAR) is an SA-mediated induced resistance
in systemic plant tissues that is effective against a broad range of
plant pathogens (Wenig et al. , 2019). LEGUME LECTIN-LIKE PROTEIN1
(LLP1) is a predicted lectin that acts in the recognition of SAR
signals, which also regulate intra- and inter-plant monoterpene
synthesis. In the non-vascular marine alga Pyropia haitanensis ,
the 1-octone-3-ol plant–plant defense signal can self-stimulate in
receiver plants and activate SA hormones (Chen et al. , 2019a).