Background/Question/Methods Plants are able to perceive and plastically respond to a myriad of biotic and abiotic challenges. Of particular interest are plant's responses to probable future damages by 'eavesdropping' on their damaged neighbors. Here we tested the hypothesis that plants are able to perceive cues of anticipated drought by eavesdropping on their droughted neighbors. A series of Pisum sativum split-root plants were grown so each one of their roots shared its rooting volume with one root of a different neighbor. 

Results/Conclusions Target plants rapidly closed their stomata following an osmotic stress induction to their neighbor. No such communication took place when the roots of the target plants did not share their rooting volume with their stressed neighbor, implying that the stress cues were transmitted among the roots rather than the shoots. Furthermore, target plants relayed the warning signals to further target plants that did not share their rooting volume with the induced neighbor. The results demonstrate a novel type of communication whereby plants not merely eavesdrop on their stressed neighbors but also relay warning signals to other unstressed plants. The results may have significant implications for the functional organization of plant populations and communities.