Induction of priming by salt stress in neighboring plants

Plants are not only able to perceive and adaptively respond to external information but also forthcoming hazards and stresses. Recent evidence suggests the role of volatile compounds as signal molecules that mediate plant interactions. Here we tested the hypothesis that unstressed plants are able to respond to stress cues emitted from their salinity-stressed neighbors and initiate a priming effect for a future salinity stress. A two step experiment was designed: in the first step (Step1), a group of Vicia faba plants (Receivers) neighbored a group of plants stressed for two weeks with 150 mM NaCl (Emitters), exchanging only airborne signals. In the second step (Step2) the Receivers and a group of unprimed plants were further treated with 150 mM NaCl, and the salinity tolerance of the two groups was compared. In Step1, after 2 hours from the application of salinity stress in the Emitters, a significant decrease of stomatal conductance was observed in the Receivers, and photosynthetic rate decreased after 24 h. A significant reduction of dry weight in Receivers was reported. Surprisingly in Step2, primed plants were better prepared to cope with the salinity stress: stomatal conductance, photosynthetic rate and relative growth rate were significantly higher than unprimed plants. This demonstrates that V. faba plants are able to perceive stress cues emitted by stressed neighbors and respond by eliciting a priming effect that prepares them for a possible future stress. Furthermore, the volatile organic compounds emitted by the stressed plants were analyzed and a list of possible airborne cues involved in this mechanism is given.