A new study of plant growth has revealed the role gravity plays in root formation and direction, including how regulatory hormones help roots navigate around obstacles before continuing their downward trajectory.
The research team behind the study suggested that unraveling this previously misunderstood process could help engineers prepare strategies for plants designed to thrive in challenging environments.
Although gravity affects all living things in one way or another, how this enigmatic yet pervasive force affects plants and their growth patterns has been an ongoing mystery. Specifically, it is known that plant roots can bend around obstacles before continuing a downward trajectory to gather more water and nutrients, a process called gravitropism. However, the exact mechanisms that let plants detect and adjust to obstacles before reacting to the force of gravity have remained unexplained.
In an attempt to unravel the mystery, experts from the University of Nottingham’s School of Biosciences and Shanghai Jiao Tang University (SJTU) performed a series of lab experiments on plant roots. Following a detailed analysis, they found that the primary factor involved a plant hormone called auxin.
According to a statement from the study authors announcing the discovery, “auxin activates a specific gene, which strengthens cell walls on the lower side of the root.” As a result, the newly “reinforced” root prevents growth below it while simultaneously enabling the root’s cells to expand, forcing growth into different directions. This combination of forces causes the root to bend when circumventing an obstacle and then resume its natural, gravity-assisted downward trajectory once the obstacle has been avoided.
“Until now, it was unclear how auxin inhibits cell expansion on the lower side of roots,” explained Dr Rahul Bhosale, Associate Professor in Nottingham’s School of Biosciences, who co-led the study with Dr. Guoqiang Huang at SJTU. “Our research resolves this longstanding question by showing that auxin promotes cell wall biosynthesis, strengthening the walls to block growth on the lower side.”
The researcher said this “dual mechanism” explains how root gravitropism is dependent on auxin, changing the way roots grow and expand through “seemingly opposite roles” of promoting and inhibiting root cell elongation. The study also unlocks how gravity affects this process, resulting in complex root trajectories that are driven by this fundamental force.
“We already knew that auxin is important for root gravitropism, but for a long time, we did not know what acts downstream of auxin,” Dr Bhosale explained. “That is what we have uncovered in this new research, which is important for fundamental understanding of how the root system works.”
In the study’s conclusion, the authors note that these findings complement their earlier work showing how plant hormones help them respond to adverse situations like drought. Taken together, the team said the twin discoveries “give a clear picture of how roots sense their environment and adjust their growth direction,” which could help engineers prepare plants to thrive in adverse conditions by controlling the root system’s gravitropism.
“Understanding the role of hormones in this much detail opens up possibilities for engineering crops that are stress resistant and can overcome obstacles in the soil,” Dr Bhosale said.
The study “Auxin controls rice root angle via kinase OsILA1-mediated cell wall modifications” was published in Science Advances.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.