ERC grant helps to understand why the upper and lower surfaces of plant leaves differ

Hanna Hõrak, Associate Professor of Molecular Plant Physiology at the University of Tartu Institute of Technology, has received a prestigious European Research Council (ERC) grant to study how cell patterns form in plant leaves. The knowledge gained will support the breeding of plants suited to future climates.

Just as the back and palm of a human hand differ in structure and function, the upper and lower surfaces of a plant leaf are also very different. A leaf surface is made up of cells. On the underside of the leaf, a quarter of all cells are stomata – controllable openings each formed by two guard cells. Through the stomata, gas exchange with the environment takes place: carbon dioxide enters the plant for photosynthesis, and water exits. Therefore, the number and arrangement of stomata on the leaf surface significantly affect plant growth, yield, and stress tolerance. For example, plants with fewer stomata cope better with drought because they lose less water. Such plants are also less susceptible to disease, as many pathogens enter the plant through stomata.

Most plant species have no stomata on the upper side of the leaf. Although some plants do produce stomata on the upper surface, these have received little attention so far. “The few studies conducted suggest that plants with stomata on the upper side of their leaves absorb carbon dioxide more efficiently and are better at photosynthesis. So upper-side stomata should be highly beneficial for plants, which raises the question: why do most species lack them?” Hõrak explained, outlining the starting point of her research.

How do stomata form on the upper side of leaves?

The aim of Hanna Hõrak’s project is to determine how stomata develop on the upper side of leaves and how their presence or absence affects plant physiology, growth, and reproduction. As the model plant, the study uses thale cress (Arabidopsis thaliana), which has stomata on both the lower and upper sides of its leaves (see figure). During the project, plant variants will be created that lack stomata on the upper side – this will make it possible to understand the role of these stomata in plant physiology, growth, reproductive success, and stress tolerance. The researchers’ work will help explain how and why the cell patterns of the upper and lower sides of leaves differ.

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Stomatal arrangement influences cereal yield

Recent research has shown that stomata on the upper side of leaves have a major impact on gas exchange in plants, particularly in cereals. In previous work, Hõrak and her colleagues found that the abundance of upper-side stomata is linked to wheat yield under field conditions.

“The ERC project will allow us to determine how stomata form on the upper side of leaves and how their abundance can be influenced in the desired direction. This will help design and breed plants with an optimal number of upper-side stomata, ensuring good yields even under challenging climate conditions of the future,” Hõrak explained.

Hanna Hõrak’s research project “Two sides to every leaf: how and why plants control stomatal distribution between leaf surfaces?” lasts for five years, and its total budget is nearly two million euros. In the latest call for proposals for the European Research Council’s Consolidator Grant, 3,121 proposals were submitted, and 349 projects from 25 countries received funding.

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Research article: Functional and developmental differences between adaxial and abaxial stomata in amphistomatous leaves