Howey N201/202, 12:30 -1:30 p.m.
Speaker: Aradhya Rajanala, Goldman Lab
Cell to Organ Modeling of Circumnutation Behaviors in Rice Roots
Navigating subterranean terrain is a complex task that plant roots confront without the use of a central nervous system. Circumnutation, the helical motion of the root tip, is a strategy that promotes root penetration and exploration. How this growth strategy is coordinated and how it reacts to different environments is largely unknown. We grew O. sativa rice roots (~ 200 um diameter) in transparent gels of different stiffnesses. Across environments, we observed a negative correlation between amplitude (the root tip angle) and frequency (how often the tip sweeps a full circle). To explain this relationship, we constructed a Discrete Element Method (DEM) simulation of the epidermal layer of a growing root (~20,000 cells in 1 cm), treating the particles of the DEM model as individual cells. Interactions between cells are implemented through bonds with time-dependent equilibrium lengths to enable cell elongation. We implement circumnutation via differential elongation, where cells grow at different speeds to induce curvature, and define the axis of circumnutation as a vector pointing from the fastest to the slowest growing cells. We find that modulating the rotational speed of this axis recapitulates the negative correlation between amplitude and frequency observed in experiment.
