Plants do not just grow on autopilot. They continuously respond to their environment, especially to light. This is because their growth and orientation determine how much sunlight they can capture for photosynthesis and convert into energy. A new study involving the Gregor Mendel Institute of Molecular Plant Biology (GMI) of the Austrian Academy of Sciences (OeAW) now shows how two key components of the light spectrum influence plant growth: blue and red light act as antagonists and together determine how plants orient themselves.
The research focuses on the liverwort Marchantia polymorpha, a representative of one of the oldest groups of land plants. Using this model, the researchers were able to demonstrate how plants process light signals to control their shape and orientation. “It all started with very simple experiments in which I grew my model plant under various monochromatic light conditions,” explains Johannes Rötzer from the GMI. “It quickly became clear that red and blue light induce two extreme forms of growth that balance each other out in white light – which contains both blue and red light.”
Plants use their “eyes”
The results paint a clear picture: blue light causes the plant to grow upward, while red light has the opposite effect. When both light colors come together – as in natural white light – a balance is created. The plant grows flat and optimally oriented. This is made possible by specialized sensors: plants “see” their environment via light receptors. “Plants perceive blue light with blue light receptors and red light with red light receptors, called phytochromes,” explains Liam Dolan of the GMI. “With these two photoreceptors acting as sort of ‘eyes,’ liverworts can detect the varying proportions of red and blue light in their environment.”
Why is this important? Because the ratio of red to blue light changes depending on the environment – for example, in the shade beneath other plants or in direct sunlight. “This antagonism helps plants adapt their growth to the respective environmental conditions,” Rötzer says. “For example, the ratio of red to blue light in the shade differs from that in sunny, light-exposed areas.” The plant thus measures its light environment and adjusts its growth accordingly. “By detecting the ratio of the two light colors in their environment, they adapt their growth direction precisely to this ratio,” Dolan says.
In addition to the light receptors, the researchers discovered another important factor in liverwort: so-called BBX proteins. These act as switches inside the cell and determine which genes are active. “In the course of the work, we came across a class of transcription factors known as BBX proteins. For some of these proteins, we were able to demonstrate a previously undiscovered role in growth regulation,” Rötzer explains. The same principle applies here as well: Two of these proteins act in opposition – it is only through their interplay that they produce the plant’s characteristic flat shape.
Significance for evolution and agriculture
The research also provides insights into the evolutionary past of plants. This is because similar mechanisms have been observed not only in liverworts but also in distantly related plant species, suggesting that this system emerged very early in evolution. According to Dolan, its origins could date back more than 500 million years – to a time when plants first colonized the land and began to actively perceive and respond to their environment.
This potentially ancient mechanism plays a central role in today’s practices: Especially in modern agriculture, where plants are often densely planted, orientation is crucial. It directly influences how efficiently plants can use sunlight for photosynthesis. “The angle at which these flat, photosynthetically active structures are oriented toward the sun is crucial to their efficiency,” Dolan explains. Even small changes can have a major impact on yield: “Simply by altering this angle, efficiency can be increased.”
A better understanding of these mechanisms could help improve crop planting practices, for example, in the context of climate change, when vegetation, cloud cover, or plant locations shift. Rötzer also sees potential here: “Findings from basic research thus provide an important foundation for specifically adapting crops to new environmental conditions, increasing their efficiency, and improving their resilience.”
Publication
Roetzer, Johannes; Asper, Beate; Meir, Zohar; Edelbacher, Natalie; Mérai, Zsuzsanna; Datta, Sourav & Dolan, Liam (2026): Antagonism between blue- and red-light signaling controls thallus flatness in Marchantia polymorpha. Current Biology.
Contact
Gregor Mendel Institute of Molecular Plant Biology
Austrian Academy of Sciences
Dr. Bohr-Gasse 3
1030 Vienna, Austria
T: +43 1 79044-9000
F: +43 1 79044-9001
E: office(at)gmi.oeaw.ac.at