by You probably don’t think much about plant roots – they’re hidden underground after all. But they are constantly changing the shape of the world. This process takes place in your garden, where plants use invisible mechanisms for their endless growth.
Scientists discovered about 15 years ago that the genes at the root tip (or more precisely, the level of proteins produced from some genes) seem to be blinking. It is still a bit of a mystery but recent research is giving us new insights.
What we do know is that this oscillation is a fundamental mechanism underlying root growth. If we understood this process better, it would help farmers and scientists design or select the best plants to grow in different types of soil and climate. With increasingly extreme weather such as droughts and floods, damaging crops around the world, understanding how plants grow is more important than ever.
To really understand how plants grow, you need to look at the processes that take place inside cells. Countless chemical reactions and changes in gene activity are happening all the time inside cells.
Some of these reactions occur in response to external signals, such as changes in light, temperature or nutrient availability. But much is part of every plant’s developmental program, encoded in its genes.
Many people think of plants as pretty vegetables. Necessary for clean air, yes, but simple organisms. A major shift in research is changing the way scientists think about plants: they are much more complex and more like us than you might imagine. This burgeoning field of science is too exciting to cover in one or two stories.
This article is part of a series, Weird Plants, which explores scientific studies that challenge the way you look at plants.
Some of these cell processes have regular oscillations – several families of molecules rhythmically appear and disappear every few hours. The most famous example is circadian rhythms, the internal clock in plants and animals (including humans).
Read more: How understanding plant body clocks could change how food is grown
Natural cycles
There are many other examples of spontaneous oscillations in nature. Some are fast such as heartbeats and the mitotic cell cycle, which is the cycle of cell division. Others, like the menstrual cycle and hibernation, are slow.
They can often be explained by an underlying negative feedback loop. This is when a process triggers a series of events that limit the activity it triggered. This seems to be the case for the root growth pulsation.
Shortly after discovering the root tip gene oscillation, scientists noticed that this pulse leaves an invisible mark. They discovered this by using fluorescent markers visible under a microscope. These marks are left in places where the root can grow side by side. This means that they provide regular cues that lead to the shape of the root system.
Its cause is currently unknown, although scientists have ruled out theories that it may be driven by circadian oscillations.
We know there are many feedback loops involved. A plant hormone called auxin appears to be critical to the process. It activates some genes coding for proteins, such as those needed for growth. Charles Darwin hypothesized the existence of axin and confirmed its chemical structure about 100 years ago.
The genes that oscillate are the “targets” of the urea. When axons enter a cell, these target genes tend to become more active. Some of these genes are involved in growth but not all. Auxin induces the elimination of “suppressors”, proteins that can inhibit gene activity. Animals also have repressors in their cells.
But these repressors are activated by the genes they block. This feedback loop may be driving the oscillations we see, but we don’t know for sure.
We know that action moves from cell to cell through a complex network of carrier proteins. The way proteins travel to parts of cells depends on the levels around the oxygen itself. This is another feedback loop. The pulsation occurs in growing roots, where cells at the tip are continuously dividing as a result of the cell cycle (which involves a separate feedback loop).
What a confrontation
Scientists often turn to mathematics to help them explain things. Researchers have used geometry since ancient times to study the visible part of plants. A branch of mathematics developed in the 19th century called Dynamical Systems Theory (DST), has given scientists some clarity on why plant roots oscillate. Scientists are using tools from DST to try to show how rounds of cell division affect patterns of action.
If these rounds of cell division were well synchronized, we could show that, in theory, this would produce a regular auxin pulse.
But this doesn’t solve the mystery because cells don’t usually divide all at once, so any pulse of action would be fairly irregular.
When my team looked under the microscope for fluorescent markers of action, we found irregularity at a distance, in the parts of the root that regularly oscillate their target genes.
This suggests that root tip gene oscillation may be linked to root growth but does not occur simultaneously with stem cell division.
Although we still have mysteries, we are now better at figuring out this enigma. It is likely that the answer lies not in one process alone, but as a result of an interaction between different processes. We know the main players, but the rules of the game they play are yet to be discovered.
Read more: Why does cauliflower look so weird? We have cracked the math behind their ‘fractal’ shape
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Etienne Farcot does not work for any company or organization that would benefit from this article, does not advise, shares in or receives funding from any company or organization that would benefit from this article, and does not disclose any relevant connections beyond their academic appointment.
