Meeting Abstract
Circumnutation is a pattern of undulatory growth observed in a diversity of plants and their organs, including roots. Little is known about the function of below-ground circumnutation, particularly in root-surface interactions. Root tip traits that allow for seeking out cracks or biopores may be advantageous, as roots have been shown to utilize these traits to penetrate into deeper soil strata. Understanding function of root circumnutation can not only help with crop breeding, but also can give insight into schemes for robots to navigate in constrained environments with minimal sensing. After observing a root coiling phenotype on flat surfaces in non-circumnutating mutant rice roots, we hypothesized that root tip circumnutation facilitates effective root-surface exploration. To test this, plates were made with holes equally spaced at different densities to systematically model a surface environment of a compact soil horizon with biopores. Mutant and wild-type (WT) rice were grown in a clear gel-based media and a high-throughput automatic imaging system acquired images to visualize the root growth. As hole density decreased, mutant primary roots showed reduced success (below 50%) in finding a hole. WT primary roots had higher success (above 80%), indicating circumnutation leads to effective flat surface exploration. We have begun to test such strategies in a macroscopic pneumatically controlled planar soft robotic root. The novel design enables the robot to extend from its tip, modeling root growth. Further, the robot possesses side-wall elements which enable tip undulation via periodic pressure changes. Future studies of the robot will test penetration probability varying nutation parameters.
