A computer-assisted mathematical image analysis method for quantifying gravitropic curvature in plant roots

Abstract

Gravitropism is the bending growth of plant organs in response to the gravity stimulus. It is essential in the deployment of an underground root system for water and nutrient acquisition, and an aboveground shoot system for photosynthesis. Quantifying such growth phenomena is critical in studying the mechanism of gravitropism. The common method of obtaining the gravitropic bend angle involves manually drawing two tangent lines along the curved organ, and measure the angle between them. The process is usually tedious, subjective, and prone to error. For precise and accurate determination of root gravitropic curvature, we developed a mathematical algorithm that minimizes the ambiguity intrinsic to manual measurement. Combined with edge detection and image segmentation techniques, the algorithm smoothes the identified root medial axis and computes the mathematical curvature at each point along the axis. The gravitropic bend angle is then determined based on the curvature profile. Accurate characterization of gravity response under various conditions is an initial step in investigating changes in gravity perception, and the cellular processes associated with it, thereby advancing our understanding of the gravisensing machinery within the cells.