Utrecht University: Computer model of root growth could lead to more eco-friendly cultivation

When you’re uprooting a plant, the network of plant roots often looks like a unorganised web. However, plant roots grow according to a fixed pattern: a main root grows downwards, with lateral roots emerging at certain intervals. Due to different amounts of nutrients and water in the soil, a lot of variation in root systems eventually develops. The question biologists would like to answer is how the regular pattern of lateral roots arises, and why some main root cells form a lateral root.

A new computer model now allows researchers to better map and predict root growth. The model was developed by researchers from Utrecht University. Together with colleagues from Wageningen University & Research and Ghent University, they experimentally demonstrated that the predictions made by the model were correct.

The new computer model provides a much more complete and realistic picture
Before the researchers started, there were already computer models and hypotheses used to explain where along the main root a plant’s lateral roots eventually develop. “All those models fall short,” says Kirsten ten Tusscher, who led the research on the new model. “None of them fully align with the results from experiments with real plants.” The model developed by Ten Tusscher and colleagues now provides a much more complete and realistic picture.

Computer simulated plant root
The computer model provides a detailed picture of all cell types in the plant root, as well as their interactions.
Wave pattern of hormones
Thanks to the new model, it becomes clear how lateral roots develop from the main root, under the influence of the plant hormone auxin. When a main root of a plant grows, the amount of auxin in the tip of the root changes regularly. The cells created at the moment when the concentration of the hormone is high, ‘remember’ this. At a later stage, when conditions are favourable, these cells grow into a side root. The cells that have experienced lower concentrations of hormone do not develop this ability.

Great detail
The new model simulates these steps, and everything involved with it, in great detail. Ten Tusscher: “In our model, we have built in what the root looks like and how the auxin hormone is transported, with as much detail as possible. The model also contains the details of the growth process, where the stem cells are located, as well as the cells that divide quickly, those that stop dividing, and those that expand. The model shows the consequences of all these interacting processes.”

Our model automatically provided what all those earlier models tried to achieve.

Prof. Kirsten ten Tusscher
Theoretical Biology
Much to the surprise of Thea van den Berg, the PhD student who carried out most of the model research, the wave pattern of auxin and the side roots emerged in the model automatically. “Then we suddenly had it!”, says Ten Tusscher. “Our model automatically provided what all those earlier models tried to achieve. And also immediately in the right spots, with the right cells and the right amounts. That, of course, was fantastic!”

After understanding how the wave patterns arose, the researchers checked whether the predictions from the model were correct. After many months of repeated experiments with real plants, this proved to be the case.

Growing plants with suitable root systems
According to the researchers, a greater understanding of root growth could help develop a more focused way of cultivating crops, with root systems that are better suited to the circumstances or wishes of a grower. In this way, it should be possible in the future to grow crops that can do with less fertiliser, pesticides or watering, for example.

A greater understanding of root growth could help develop a more focused way of cultivating crops.
To some extent, crops can adapt their roots to the environment. But sometimes they can use some help in doing so, in order to achieve greater yields. For example, if the soil has too little phosphate, the main root remains shorter and the lateral roots grow horizontally. The reason for this is that phosphate is fairly close to the surface. The plant benefits from having more roots close to the scarce phosphate, and therefore keeps its roots near the surface as much as possible.

On the other hand, nitrate, for example, is usually much deeper in the soil. If the amount of nitrate is limited, the root will be very deep, with a limited number of long steep lateral roots.

Optimising plant behaviour in crops
“We would very much like to understand this ‘behaviour’ of plants in order to to further optimise it in crops”, says Ten Tusscher. The researcher recommends using the principles of the new model for this. “Biologists often resort to separate explanations for changes in the length of the main root and in the number of lateral roots. But our model shows that changes in the growth of the main root automatically lead to changes in the number of lateral roots. This means you have to examine both of these properties simultaneously.”