When two become one: perceptual completion in pea plants.

Pea plants depend on external structures to reach the strongest light source. To do this, they need to perceive a potential support and to flexibly adapt the movement of their motile organs (e.g. tendrils). In natural environments, there are several above- and belowground elements that could impede the complete perception of potential supports. In such instances, plants may be required to perform a sort of perceptual "completion" to establish a unified percept. We tested whether pea plants are capable of performing perceptual completion by investigating their ascent and attachment behavior using three-dimensional (3D) kinematic analysis. Pea plants were tested in the presence of a support divided into two parts positioned at opposite locations. One part was grounded and perceived only by the root system. The remaining portion was elevated from the ground so that it was only accessible by the aerial part. Control conditions were also included. We hypothesized that if pea plants are able to perceptually integrate the two parts of the support, then they would perform a successful clasping movement. Alternatively, if such integration does not occur, plants may exhibit disoriented exploratory behavior that does not lead to clasping the support. The results demonstrated that pea plants are capable of perceptual completion, allowing for the integration of information coming from the root system and the aerial part. We contend that perceptual completion may be achieved through a continuous crosstalk between a plant's modules determined by a complex signaling network. By integrating these findings with ecological observations, it may be possible to identify specific factors related to support detection and coding in climbing plants.