Abstract

Plants are complex organisms living in a changing environment and, because of that, they have to develop many strategies to perceive physical, chemical or biological stimuli to characterize their momentary environment. Our study aims to understand how plants can interact with those stimuli to communicate with other plants present in their environment. We hypothesized that this communication appears through the root system and we focused our work to apprehend the possible vectors. 
First, in-vitro experimentation was developed by a group of American students in order to identify four components responsible for the communication between plants. They conclude: " this pilot study has indicated that neighbor plants communicate underground when submitted to different concentrations of nutrients".
Then, we developed models to predict the vector of the signal with two hypotheses: by an active transport through mycorrhizae or by a passive transport through diffusion in the medium.  Based on the response time noticed in the American’s experiment, our results showed that the observed response happened too quickly to be explained by the communication ways we tested.    

Introduction

It is known that plants react to many stimuli that are present in the growing environment, such as physical (i.e. light, temperature, humidity), chemical (i.e. nutrient concentration, volatile compound, chemical signal in the ground, ...) or biological (i.e. pathogens, symbiont).   
How plant can interact with those stimuli? Via allelopathy, it is accepted that they are able to communicate between them. But, what are the vector of this communication? The soil, the air, the water or some living organisms.  In this study case, we tried to explore this question following two steps: 
The first one is based on an in-vitro experimentation developed by a group of American students. Their purpose was to identify four components responsible of the communication between plants: a clear motivation or reason for the communication, the presence of a signal and/or channel, a receiver, and a clear response.  To identify the interaction between plants, they build an in-vitro system physically separated into three sections, each of them had a different nutrition condition. They hypothesized that this discrimination in term of nutritive context could be the reason to induce communication. In order to test this hypothesis, one plant has been placed in each compartment. Therefore, they supposed that the signal would be transmitted by chemical molecules excreted by the roots, called exudate, and that the channel will be passive, through the medium or active via the mycorrhizae, that is the reason why they used pre-mycorrhized plants. To allow the perception of the signal by a receiver, the roots of each plant were placed in a shared compartment without any physical contact in the middle of the system (Figure 1).  Finally, they wanted to observe a clear response, such as a root direction growth that would indicate the perception of a more favorable nutritive context.