Delayed control driven oscillations in plant roots

TL;DR

This paper presents a minimal nonlinear model explaining oscillatory root growth in Arabidopsis based on a delay hypothesis, supported by experimental data and applicable across plant species.

Contribution

The authors develop a simple delay-based model predicting root oscillations and validate it with experimental data across different plant species.

Findings

Root oscillations in Arabidopsis are explained by a delay-driven model.

Experimental data supports the fourfold delay-period relation.

The model is applicable to diverse plant species.

Abstract

Arabidopsis roots show oscillatory growth patterns on homogeneous agar surfaces, whereas other plants, such as maize, do not. Although several explanations have been proposed, a simple and general model that makes testable predictions across species has been lacking. Roots sense gravity and correct their growth direction towards the vertical. Motivated by recent evidence for a time delay in this gravitropic correction, we develop a minimal nonlinear model based on the delay hypothesis that predicts whether a root oscillates or grows vertically downwards. The model identifies a fourfold relation between the delay and time period, robust across different response functions. Analysing images of Arabidopsis, we find that the mode of the oscillatory arc length is not significantly different between inclined and vertical growth conditions. The quantitative agreement between the experimentally measured oscillatory arc length and the arc length estimated from estimated root growth speed and response delay supports this fourfold delay-period rule for delay-driven root oscillations. The simplicity of our model allows for a direct comparison with data from diverse plant species.