Long-distance hormone transport via the phloem

Collis, Heather L.; Owen, Markus R.; Band, Leah R.

Abstract

Several key plant hormones are synthesised in the shoot and are advected within the phloem to the root tip. In the root tip, these hormones regulate growth and developmental processes, and responses to environmental cues. However, we lack understanding of how environmental factors and biological parameters affect the delivery of hormones to the root tip. In this study, we build on existing models of phloem flow to develop a mathematical model of sugar transport alongside the transport of a generic hormone. We derive the equations for osmotically driven flow in a long, thin pipe with spatially varying membrane properties to capture the phloem loading and unloading zones. Motivated by experimental findings, we formulate solute membrane transport in terms of passive and active components, and incorporate solute unloading via bulk flow (i.e. advection with the water efflux) by including the Staverman reflection coefficient. We use the model to investigate the coupling between the sugar and hormone dynamics. The model predicts that environmental cues that lead to an increase in active sugar loading, an increase in bulk flow sugar unloading or a decrease in the relative root sugar concentration result in an increase in phloem transport velocity. Furthermore, the model reveals that such increases in phloem transport velocity result in an increase in hormone delivery to the root tip for passively loaded hormones.

Citation

Collis, H. L., Owen, M. R., & Band, L. R. (2023). Long-distance hormone transport via the phloem. Journal of Theoretical Biology, 562, Article 111415. https://doi.org/10.1016/j.jtbi.2023.111415

• Journal Article Type: Article
• Acceptance Date: Jan 10, 2023
• Online Publication Date: Feb 2, 2023
• Publication Date: Apr 7, 2023
• Deposit Date: Feb 7, 2023
• Publicly Available Date: Feb 7, 2023
• Journal: Journal of Theoretical Biology
• Print ISSN: 0022-5193
• Electronic ISSN: 1095-8541
• Publisher: Elsevier BV
• Peer Reviewed: Peer Reviewed
• Volume: 562
• Article Number: 111415
• DOI: https://doi.org/10.1016/j.jtbi.2023.111415
• Keywords: Applied Mathematics; General Agricultural and Biological Sciences; General Immunology and Microbiology; General Biochemistry, Genetics and Molecular Biology; Modeling and Simulation; General Medicine; Statistics and Probability
• Public URL: https://nottingham-repository.worktribe.com/output/16230902
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0022519323000115?via%3Dihub
• Additional Information: This article is maintained by: Elsevier; Article Title: Long-distance hormone transport via the phloem; Journal Title: Journal of Theoretical Biology; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.jtbi.2023.111415; Content Type: article; Copyright: © 2023 The Author(s). Published by Elsevier Ltd.