How plants adapt their root growth to changes of nutrients

Date:
January 5, 2021
Source:
Institute of Science and Technology Austria
Summary:
Nitrogen is one the most essential nutrients for plants. Its
availability in the soil plays a major role in plant growth and
development, thereby affecting agricultural productivity. Scientists
were now able to show, how plants adjust their root growth to
varying sources of nitrogen. They give insights in the molecular
pathways of roots adaptation.



FULL STORY ==========================================================================
Like any other plant, Arabidopsis thaliana or mouse-ear cress, needs
nitrogen to survive and thrive. But, like maize, beans and sugar beet,
it prefers nitrogen in the form of nitrate, growing better on nitrate
rich soil. Whereas, pine and rice for example preferentially grow on
ammonium nutrition, another form of the key macronutrient nitrogen. If
the concentration or the availability of the different forms of nitrogen fluctuate, plants have to adapt quickly. "One of the most important
questions is, what is the role of plant hormones in adaptation to the
nitrogen availability? How do the machineries within a plant cope with
their changing environment?" asks Eva Benkova', developmental biologist
and Professor at the Institute of Science and Technology (IST) Austria.


========================================================================== Finding the balance In search of answers, Krisztina O"tvo"s, postdoctoral fellow in the research team of Eva Benkova', together with colleagues
from the Universidad Polite'cnica de Madrid, the Pontifical Catholic
University of Chile, the Austrian Institute of Technology and the
University of Montpellier, looked at two extremes: They compared how Arabidopsis seedlings that were grown exclusively on ammonium reacted,
once the scientists transferred them to media containing either ammonium
or nitrate.

If a plant lives in suboptimal soil, it tries to maintain its root growth
as long as possible to reach a more suitable form of nitrogen. The major processes, which maintain the root growth, are the cell proliferation in
the meristem, a plant tissue consisting of undifferentiated cells, and
the cell expansion. The plant has to find a good balance between these
two. Provided with ammonium, the form of nitrogen Arabidopsis is not so
fond of, the meristematic zone of the cress produced less cells. Instead,
they very quickly elongated. "Once we moved the plants to the nitrate,
suddenly the meristem became bigger, more cells were produced and
there was a different kinetics in cell expansion," says Benkova'. "Now Arabidopsis could afford to put more energy into cell division and
optimized its root growth differently." Controlling the hormone flow
Whether the plant invests in cell proliferation or cell elongation is instructed by the level of auxin. This plant hormone is essential for
all developmental processes. It is transported in a very controlled way
from one cell to the next by special auxin transporters. The proteins
that control the transport of auxin out of the cells, so called efflux carriers, regulate the flow of auxin depending on which side of the cell
they are sitting. Benkova' and her team were especially interested in the
auxin transporter PIN2, which mediates the flow of auxin at the very root
tip. The researchers were able to identify PIN2 as the main factor to set
up the balance between cell division and cell elongation. "We observed
that once we moved plants onto the nitrate, the localization of PIN2
changes. Thereby, it changes the distribution of auxin." The activity of
PIN2 on the other hand is affected by its phosphorylation status. "What
really surprised us was that one modification, the phosphorylation of
such a big protein like an efflux carrier, can have such an important
impact on the root behavior," Benkova' adds. Furthermore, the amino
acid of PIN2 that is the target of the phosphorylation, is present in
many different plant species, suggesting that PIN2 might be universally involved in other plant species adaption strategies to changing nitrogen sources. In a next step, the researchers want to understand the machinery
that controls the change of the phosphorylation status.

A very close look "The present study is the result of the input of
many different people from cell biologists and computer scientists to
people working in advanced microscopy. It really is a multidisciplinary approach," Eva Benkova' emphasizes. In order to take a close look at the processes within Arabidopsis' roots, for example, the biologists used
a vertical confocal microscope -- a tool especially adapted at the IST
Austria to suit the researchers' needs.

Instead of a horizontal stage the microscope uses a vertical one, which
allows you to observe the plant growth the way it naturally does --
along the gravity factor. With its high resolution Benkova' and her
team were able to observe how the cells within Arabidopsis' roots were
dividing and expanding in real time.

In a previous project, researchers at the IST Austria won Nikon's Small
World in Motion video competition, showing live-tracking of a growing
root tip of Arabidopsis thaliana under the microscope.


========================================================================== Story Source: Materials provided by Institute_of_Science_and_Technology_Austria. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. O"tvo"s K, Marconi M, Vega A, O' Brien J, Johnson A, Abualia R,
Antonielli L, Montesinos JC, Zhang Y, Tan S, Cuesta C, Artner C,
Bouguyon E, Gojon A, Friml J, Gutie'rrez RA, Wabnik K, Benkova'
E. Modulation of plant root growth by nitrogen source-defined
regulation of polar auxin transport. EMBO Journal, 2021 DOI:
10.15252/embj.2020106862 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/01/210105084658.htm

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