Plants use their roots to measure the concentration of effective manganese in the soil

Every living thing needs manganese as an essential nutrient
.
In plants, for example, it plays an important role
in the process of splitting water into oxygen and hydrogen in photosynthesis.
A team of German and Chinese researchers demonstrated for the first time how plants perceive manganese deficiency at the molecular level and what processes
subsequently occur in plants with the model species thale cress thale thaless.
The researchers found that a hitherto undiscovered group of cells at the root of the plant plays a decisive role
.
The scientists hope that the results of their work will lead to a future way to make plants more resistant to manganese deficiency, a condition that often occurs in alkaline and calcareous
soils.

Professor Jrg Kudla from the Institute of Plant Biology and Biotechnology at the University of Münster (Germany) is one of the lead authors of the study, as he says: "There has been a lot of research focused on which proteins within cells are involved in the absorption and transport
of manganese.
But how the balance of manganese is regulated at the level of
the organism is completely unknown.
Since calcium is involved in many other regulatory processes in plants as a messenger substance, the researchers asked themselves whether calcium also plays a role
in regulating manganese balance.

Manganese deficiency triggers an oscillating calcium signal

The team found a special population of cells at the root of the plant and named it "manganese-sensitive niche.
"
Unlike all other root cells, these cells exhibit a special response when manganese is deficient: as long as manganese is deficient, calcium concentrations within the cells rise and fall
several times in a row.
Each oscillation lasts approximately 30 minutes
.
"No one has previously observed this multicellular oscillation of calcium concentration, which is established by the coordinated occurrence of individual cellular calcium signaling in plants," Kudela
said.
Only a few hundred cells work together to form a signal
.
Epidermal cells — the outermost root cells — are the first to begin to increase calcium concentrations
.
Then, before the whole process is reversed, cells located deeper inside gradually follow
.

A third stimulus-specific "sensitive niche" has now been discovered

In earlier work, researchers led by Jrg Kudla have identified two other "sensitive niches" in other regions of the root—one sensitive to potassium and one sensitive to
sodium.
Here, too, roots respond to changes
in ion concentrations in the environment by generating multicellular calcium signals in specific cell populations.
However, the researchers did not observe any oscillations — unlike in manganese-sensitive niches
.

In their current study, the researchers found that calcium oscillations triggered by manganese deficiency activate two special enzymes — so-called calcium-dependent protein kinases (CPK21 and CPK23) — and these two enzymes, for their part, stimulate manganese absorption
.
"As kinases are released from calcium, these substances become inactive
again.
Our hypothesis is that each oscillation restarts this process until the plant gets enough manganese absorption," Kudela said
.
The manganese transporter NRAMP1 is responsible for transporting manganese to the cells of the root, which is part of
this process.
The protein kinases CPK21 and CPK23 interact with this transporter to regulate manganese absorption
by phosphorylating a specific amino acid (Thr498).

To demonstrate the occurrence of calcium signaling, the researchers used high-resolution microscopy and, for the first time, an ultrasensitive molecular calcium biosensor
.
Biosensors can often observe changes in the concentration of biologically active substances such as calcium in
cells and tissues.
The team combined these studies, including "biosensor technology in living organisms to genetic, cell biology and biochemical approaches to clarify underlying molecular mechanisms
.
" In addition to Münster's researchers, scientists from the School of Life Sciences of Northwest A & F University in Shaanxi and the Institute of Biotechnology of the Chinese Academy of Agricultural Sciences, as well as scientists from Martin Luther University in Germany, also participated in the research
.