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Plant leaves send signals to their roots on dry days telling them to keep digging deeper for water

It’s a known fact that plants have an uncanny knack for survival. They have learned to send signals and also use hormones called ABA. These stratgies regulate their internal and external systems.

Scientists from the Sainsbury Laboratory Cambridge University (SLCU) have now shed light on a fascinating new piece of the survival puzzle.

According to their recent findings, plants have a clever way of dealing with dry conditions. They send signals from the leaves down to the roots.

Plants send signals using “shoot-to-root signaling”

This is a new pathway the scientists call “shoot-to-root signaling.” This ensures that the roots keep growing towards water, even when the surrounding soil is dry.

Here’s a quick science recap for you. When plants are under drought stress, they produce a hormone known as abscisic acid (ABA). This hormone has long been considered a “drought stress” hormone.

How does abscisic acid (ABA) help plants send signals?

Until recently, scientists held the belief that the roots produced ABA. Then, it traveled to the leaves to aid the plant in conserving water. The hormone works by closing tiny leaf pores, known as stomata. These stomata prevent the plant from losing water.

But science always has room for new discoveries. Over the past few years, plant scientists have uncovered more about this process. They found out that roots send ABA to the leaves. In addition, leaves can also produce their own ABA.

Here comes the surprising part. The SLCU team, led by Dr. Alexander Jones, has found out that leaves can do even more.

Leaves exposed to low humidity or dry air send a signal down to the roots. This signal triggers the roots to keep growing using ABA.

This discovery was a big surprise to scientists. Scientists have always considered ABA a growth stopper, not a growth starter.

Why is ABA finding significant?

Well, this “shoot-to-root signaling” potentially helps the plant to look for water deeper in the soil. This gives the plant a better chance of surviving in dry conditions.

The signaling pathway could act as an early warning system. It allows the plant to prepare for upcoming water shortages.

How did the scientists make this discovery?

The research team developed and used a new, next-generation biosensor, named ABACUS2. This biosensor helped them to detect ABA levels in living plants. It also allowed them to see exactly how environmental stress, such as dry conditions, could increase these hormone levels.

“We’ve known for several years that, at low humidity, plants prioritize root growth,” said Dr. James Rowe, the first author of the study.

He further added, “The molecular mechanisms behind this phenomenon have been a mystery until ABACUS2 allowed us to measure ABA concentrations at the cellular level in Arabidopsis thaliana seedlings.”

Rowe continued, “We saw that when the leaves experience low humidity stress that ABA accumulates in the root tips. The leaves are reacting to the dry air and telling the roots to continue growing, enabling plants to maintain foraging of deeper soil for water.”

ABA delivers more surprises

What’s even more surprising is that this growth-promoting role of ABA goes against its traditional understanding. ABA is usually considered a growth inhibitor.

However, this study shows that it can also stimulate root growth. This helps plants to continue their search for water in dry conditions.

“The root ABA comes from the phloem, which transports sugars and hormones from the shoot and is unloaded in the root tip. ABA signaling can fine-tune root growth as humidity varies,” said Dr. Alexander Jones.

ABA can help scientists manage climate change impact

This discovery is not just academically interesting. It also has practical implications. This is especially true for understanding how crops adapt to changing environmental conditions.

For instance, it offers insights into the potential reactions of crops, grown under irrigation, when they encounter dry air and wet soil. This is a condition that’s becoming increasingly common with climate change.

As with all scientific discoveries, there’s more to be learned. The SLCU team plans to dig deeper into these mechanisms.

The next study will focus on the signals between the leaves and roots under drought and low humidity stress. Their findings so far already mark a significant step forward in understanding the intricate survival tactics of plants.

More about plants’ communication systems

Plants have intricate internal and external communication systems. These incredible natural mechanisms allow them to adapt to their environment and interact with other organisms. Plants also send signals to coordinate their own growth and development.

Plant communication systems involve a multitude of chemical signals. These include hormones and secondary metabolites. They also send physical signals, such as electrical impulses and mechanical pressure.

Internal Communication

The internal communication within a plant is mainly regulated by plant hormones. One part of the plant produces these hormones and transports them to other parts. There, they exert their effects.

Plants have several classes of hormones, each with a unique role:


These primarily participate in cell elongation, apical dominance, and root development.


They promote cell division and bud formation.


They stimulate stem elongation and seed germination.

Abscisic Acid (ABA)

It participates in many plant developmental processes, including seed and bud dormancy, controlling organ size, and responding to environmental stresses like drought.


It regulates many aspects of growth and development, including ripening of fruit, shedding of leaves, and aging.

Plants also have a vascular system, comprising the xylem and phloem. These act as an information superhighway.

The xylem transports water and minerals from the roots to the rest of the plant. The phloem transports sugars, hormones, and other signaling molecules from the leaves.

From there, they are produced via photosynthesis to the rest of the plant.

In addition to chemical signaling, plants can also use electrical signals to communicate internally. These signals can be triggered by environmental stimuli.

Disturbances such as injury or changes in light trigger these signals. They can then propagate rapidly throughout the plant, triggering various responses.

External Communication

Plants also communicate with their external environment and interact with other organisms.

Chemical Signaling

Plants can release volatile organic compounds (VOCs) into the air, which can serve various purposes. Some VOCs can attract pollinators, while others can ward off herbivores.

Some plants can even release VOCs that signal nearby plants of the same species about an imminent threat, like an insect attack, prompting those plants to start producing defensive chemicals.

Physical Interactions

Plants can also respond to physical contact. For instance, climbing plants have specialized structures called tendrils that can sense contact with a physical support and respond by coiling around it.

Light Signaling

Plants can perceive and respond to light. This is crucial for processes such as phototropism (growth towards light) and photoperiodism (response to day length). They do this using photoreceptor proteins that can sense different wavelengths of light.

In conclusion, plant communication is a complex network of chemical and physical signals. They regulate plant growth, development, and interactions with the environment.

These sophisticated communication systems enable plants to thrive in a wide range of habitats. This is the main reason we see plants everywhere from arid deserts to lush rainforests.

Researchers continue to uncover more about these fascinating systems. Their studies help us better understand how plants adapt to their environment and respond to stress.

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