Plants have colonized the vast majority of the Earth’s surface. So what is the key to their success?
People often think of plants as simple, no-nonsense life forms whose roots may live in one place, but the more scientists learn about plants, the more complex and responsive we realize they are. They are excellent at adapting to local conditions, plants specializing in making the most of what is close to where they grow.
Learning about the intricacies of plant life is more than just inspiring wonders in people. Studying plants is also about making sure we can still grow crops in the future as climate change makes our weather more extreme.
Environmental cues shape the growth and development of plants, for example, many plants use daylight hours as a cue to trigger flowering. The plants’ hidden half, the roots, also use cues from their surroundings to ensure they are optimally shaped to feed in water and nutrients.
Roots protect plants from stresses such as drought by adapting their shape (branching to increase their surface area, for example) to find more water. But until recently, scientists didn’t understand how roots sense the presence of water in the surrounding soil.
Water is the most important molecule on earth, too much or too little can destroy an ecosystem. The devastating impact of climate change (as seen recently in Europe and East Africa) is making floods and droughts more common. As climate change makes rainfall patterns increasingly erratic, learning how plants respond to water shortages is vital to making crops more resilient.
A team of botanists, soil scientists and mathematicians recently discovered how plant roots adapt their shape to maximize water uptake. Roots normally branch horizontally, but they temporarily stop branching when they lose contact with water (such as growing through an air-filled vacuole in the soil) and the roots resume branching only once the connection is re-established. with wet soil.
The research team found that plants use a system called water signaling to manage where roots branch out in response to the availability of water in the soil.
A water signal is the way plants sense where water is, not by measuring moisture levels directly, but by sensing other soluble molecules moving with the water inside plants. This is only possible because plant cells (as opposed to animal cells) are linked together. some with small pores.
These pores enable water and small soluble molecules (including hormones) to move together between root cells and tissues. When the root of a plant absorbs water, it travels through the outer epidermal cells.
The outer root cells also contain a branching-promoting hormone called auxin. Water uptake causes branching by moving the auxin inwards into the inner root tissues. When water is not externally available, for example when the root grows through an air-filled vacuole, the root tip He still needs water to grow.
So when the roots can no longer absorb water from the soil, they have to rely on water from their veins deep in the roots. This changes the direction of the water’s movement, causing it to now move outwards, disrupting the flow of the branching hormone auxin.
The plant also makes an anti-branching hormone called ABA in its root veins. ABA moves with the water flow as well, in the opposite direction of the auxin. So when the roots drop on water from the veins of the plants, the roots also attract the anti-branching hormone towards themselves.
ABA halts root branching by closing all the tiny pores that connect root cells — somewhat like blast doors on a ship. This closes the root cells from each other and stops the auxin from moving freely with water, preventing root branching. This simple system allows plant roots to adjust their shape according to local water conditions. It’s called xerobranching (pronounced zerobranching).
The study also found that plant roots use a similar system to reduce water loss as their buds. Leaves stop water loss during drought conditions by closing tiny pores called stomata on their surfaces. Closing of stomata is also triggered by the hormone ABA. Similarly, in roots, ABA reduces water loss. Water loss by closing the nanopores called plasmodesmata that connect each root cell together.
The roots of tomatoes, cress, corn, wheat, and barley respond to moisture in this way, despite developing in different soils and climates. For example, the tomato originated in the deserts of South America, while the cress comes from the temperate regions of Central Asia.
This indicates that xerobranching is a common feature in flowering plants, which are more than 200 million years older than non-flowering plants such as ferns.
Root ferns, one of the early-growing land plant species, do not respond to water in this way. Their roots grow uniformly. This indicates that flowering species are better at adapting to water stress than earlier land plants such as ferns.
Flowering plants can colonize a wider range of ecosystems and environments than non-flowering species. Due to rapid changes in precipitation patterns around the world, plants’ ability to sense and adapt to a wide range of soil moisture conditions is more important now than ever.