Proc. Natl Acad. Sci. USA http://doi.org/8cc (2015)

Plant roots can take on some weird and wonderful morphologies, but understanding how these patterns form is complicated by the difficulty in imaging through soil. Tzer Han Tan and colleagues have remedied this by growing plants whose roots are embedded in a transparent hydrogel — finding similarities between the way that roots and single-celled organisms target nutrients.

By tuning the growth with the help of a rigid barrier, Tan et al. were able to observe straight, coiled and wavy morphologies. They interpreted their measurements by drawing inspiration from bacterial motility. In a way reminiscent of the run-and-tumble method that E. coli uses to search for food, the roots they imaged branched out according to a grow-and-switch mechanism described by a 2D biased random walk. Switching events were regulated by the roots' sensitivity to gravity, in analogy with the way E. coli responds to chemical cues.