Plants may not have eyes and ears, but they can recognize their siblings, and researchers at the University of Delaware have discovered how.

The ID system lies in the roots and the chemical cues they secrete.

The finding not only sheds light on the intriguing sensing system in plants, but also may have implications for agriculture and even home gardening.

The study, which is reported in the scientific journal Communicative & Integrative Biology, was led by Harsh Bais, assistant professor of plant and soil sciences at the University of Delaware.

Canadian researchers published in 2007 that sea rocket, a common seashore plant, can recognize its siblings -- plants grown from seeds from the same mother.

Susan Dudley, an evolutionary plant ecologist at McMaster University in Hamilton, Ontario, and her colleagues observed that when siblings are grown next to each other in the soil, they “play nice” and don't send out more roots to compete with one another.

However, the moment one of the plants is thrown in with strangers, it begins competing with them by rapidly growing more roots to take up the water and mineral nutrients in the soil.

Bais, who has conducted a variety of research on plant signaling systems, read Dudley's study and wanted to find the mechanism behind the sibling recognition.

“Plants have no visible sensory markers, and they can't run away from where they are planted,” Bais says. “It then becomes a search for more complex patterns of recognition.”

Working in his laboratory at the Delaware Biotechnology Institute, a major center for life sciences research at UD, Bais and doctoral student Meredith Biedrzycki set up a study with wild populations of Arabidopsis thaliana.

They utilized wild populations to avoid issues with this common laboratory-bred species, which “always has cousins floating around in the lab,” Bais says.

In a series of experiments, young seedlings were exposed to liquid media containing the root secretions or “exudates” from siblings, from strangers (non-siblings), or only their own exudates.

 

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The length of the longest lateral root and of the hypocotyl, the first leaf-like structure that forms on the plant, were measured.

Additionally, in one experiment, the root exudates were inhibited by sodium orthovanadate, which specifically blocks root secretions without imparting adverse growth effects on roots.

The exposure of plants to the root exudates of strangers induced greater lateral root formation than exposure of plants to sibling exudates. Stranger recognition was abolished upon treatment with the secretion inhibitor.

Biedrzycki did the painstaking laboratory research, rotating more than 3,000plants involved in the study every day for seven consecutive days and documenting the root patterns.