Short signalling distances make plant communication a soliloquy

Area of Science:

• Plant biology
• Chemical ecology
• Plant defense mechanisms

Background:

• Plants emit volatile organic compounds (VOCs) in response to herbivore or pathogen attacks.
• These VOCs can induce defense responses in neighboring plants, a phenomenon termed 'plant communication'.
• This inter-plant signaling raises evolutionary questions as it benefits unrelated, potentially competing individuals.

Purpose of the Study:

• To investigate the signaling distances of VOCs in lima bean plants under field conditions.
• To determine if VOCs primarily mediate within-plant or between-plant defense signaling.
• To assess the ecological relevance of VOC signaling distances in natural plant clusters.

Main Methods:

• Field experiments using wild-type lima bean (Phaseolus lunatus).
• Quantification of the distances over which airborne resistance-inducing volatiles travel.
• Analysis of leaf distribution within lima bean clusters at varying distances from signaling leaves.

Main Results:

• Induced airborne resistance in receiver plants was observed up to 50 cm from the signaling emitter.
• In undisturbed lima bean clusters, over 80% of leaves within 50 cm of a signaling leaf belonged to the same plant.
• At distances greater than 50 cm, the proportion of same-plant leaves dropped below 50%.

Conclusions:

• Lima bean plants primarily utilize VOCs for within-plant signaling, activating defenses in nearby leaves of the same individual.
• The effective signaling distance of VOCs under natural conditions favors intra-plant communication over inter-plant signaling.
• This finding provides an evolutionary explanation for VOC-mediated defense signaling, benefiting the emitter by enhancing its own overall fitness.