Arabidopsis thaliana, or mouse-ear cress, requires nitrogen to live and flourish, like any other plant.
But it prefers nitrogen in the form of nitrate, like corn, beans and sugar beets, and grows best on soil rich in nitrate.
For example, pine and rice, on the other hand, prefer to grow on ammonium food, another source of the essential nitrogen macronutrient.
Plants must respond rapidly when the concentration or availability of various sources of nitrogen fluctuates. “One of the most important questions is what role plant hormones play in adapting to nitrogen availability. How do the mechanisms within a plant cope with its changing environment?”One of the most important questions is what role plant hormones play in adapting to the availability of nitrogen. How do the mechanisms within a plant deal with its changing environment?
Searching for harmony
In pursuit of answers, Krisztina Ötvös, a postdoctoral researcher on Eva Benková’s research team, and colleagues from the Universidad Politécnica de Madrid, the Pontifical Catholic University of Chile, the Austrian Institute of Technology and the University of Montpellier studied two extremes: they compared how Arabidopsis seedlings grown exclusively on ammonium reacted after scientists transferr
If a plant lives in suboptimal soil, it attempts as long as possible to sustain its root growth to obtain a more sufficient form of nitrogen.
Cell proliferation in the meristem, a plant tissue composed of undifferentiated cells, and cell expansion are the primary procedures that sustain root growth.
A good balance between these two must be sought by the plant. Supplied with ammonium, the nitrogen form that Arabidopsis does not like, fewer cells were formed by the meristem zone of the cress.
They elongated very easily instead. The meristem suddenly became larger as soon as we switched the plants to nitrate, more cells were created, and there were different kinetics in cell expansion,”As soon as we switched the plants to nitrate, the meristem suddenly got bigger, more cells were produced, and there were different kinetics in cell expansion,” “Now Arabidopsis could afford to put more energy into cell division and optimized its root growth differently.”
Hormone flow monitors
The amount of auxin shows whether the plant is investing in cell proliferation or cell elongation.
For all developmental cycles, this plant hormone is fundamental.
It is transferred by special auxin carriers in a very regulated way from one cell to the next.
Depending on which side of the cell they are located, the proteins that govern the transfer of auxin from the cell, known as efflux carriers, regulate the flow of auxin.
The auxin transporter PIN2, which mediates the flow of auxin right at the root tip, was of particular interest to Benková and her team.
As the primary factor that balances cell division and cell elongation, the researchers were able to recognize PIN2. We found that once we transferred the plants to nitrate, the localization of PIN2 shifts.
The distribution of auxin also changes this.
Arabidopsis root tip growth supplied with ammonium vs. nitrate is seen in the video.
Krisztina Ötvös / IST Austria Credit:
On the other hand, the activity of PIN2 is affected by its phosphorylation status. Benková continues, “What really surprised us was that a modification, the phosphorylation of such a big protein as an efflux carrier, can have such a big impact on root behavior,”
In addition, in many different plant species, the PIN2 amino acid that is the phosphorylation target is present, indicating that PIN2 could be uniformly involved in other plant species’ adaptation strategies for evolving nitrogen sources.
The researchers hope to understand the machinery that regulates the change in the status of phosphorylation as the next step.
Looking very closely at myself
This research is the result of feedback from several different individuals, from cell biologists to computer scientists to advanced microscopy staff.
It really is a multidisciplinary approach,’ Eva Benková stresses.
In order to take a closer look at the processes at the root of Arabidopsis, for example, the biologists used a vertical confocal microscope, a method specifically adapted to meet the needs of researchers at IST Austria.
The microscope uses a vertical one instead of a horizontal stage that enables plant growth to be examined along the gravity force as it happens in nature.
Benková and her team were able to observe in real time with its high resolution how the cells in the roots of