Heal the wound or form roots? It depends on water availability
A torn tomato leaf that ends up on the ground sometimes develops roots from the wound, but other times it seals the wound with healing tissue. A study led from SLU now shows that water availability is the key factor that controls the fate of the leaf in the event of such damage.
“We believe our work may be a milestone in the development of methods for propagating plant material,” says Abdul Kareem, lead author of the study and researcher in the group of Professor Charles Melnyk. “This could involve anything from tissue culture to air layering, a method where root formation is stimulated on a branch or stem while it is still attached to the mother plant.”
Plants have an extraordinary ability to adapt. This can involve adapting growth to changes in the environment, such as shading or water shortage, but also responses to damage. So, what determines whether a damaged plant part will form new roots or promote healing? And why is this so important for biotechnology and agriculture?
A previous study discovered that detached leaf formed roots when the wound touched the ground, while it formed a thick mass of cells (callus) when the wound was in the air. New research from SLU shows that it is the water supply that determines what starts to grow out of the wound: When the wound touched a surface with much water available it formed roots, but touching a drier surface led to callus. The discovery was made in studies of thale cress (Arabidopsis thaliana), an important model organism in plant research, but the same phenomenon was also seen in tomato leaves.
“This suggests that the same process can occur in many plant species,” say Ellen Fasth and Anna van Wüllen, doctoral students at SLU and co-authors.
Affects gene activity as well as hormone levels
In their study, the researchers also investigated what happens at the molecular level when plants are wounded. One thing they discovered was that hundreds of genes are activated or repressed depending on water availability, and that hormonal changes occur at the same time, especially when it comes to the growth hormone auxin.
Very early after detachment, several genes that are known to be related to root development were found to be specifically active under high water conditions. Under dry conditions, genes that are related to callus generation were activated instead. This means that the availability of water, through hormonal effects, determines what will happen in the leaf very soon after wounding.
Important applications
Both root formation and callus regeneration are extremely interesting for plant scientists, but there are also important applications in agriculture, horticulture, forestry and environmental protection, where tissue culturing – in which whole plants can be regenerated from a leaf – can bring numerous practical and economic benefits. In tissue culture, there has been a strong focus on optimising the content of plant nutrients and hormones in the medium, while the role of water availability has been largely overlooked.
The researchers believe that their demonstration of the crucial importance of water availability for root formation paves the way for future applications in the agricultural industry and biotechnology.
Contact persons
Anna Van Wüllen, Doctoral Student
Department of Plant Biology
Swedish University of Agricultural Sciences
+46 18 673245, anna.van.wullen@slu.se
Charles Melnyk, Professor
Department of Plant Biology
Swedish University of Agricultural Sciences
+4618673238, charles.melnyk@slu.se
The article
Kareem, A., van Wüllen, A. K., Zhang, A., Walckiers, G., Fasth, E., & Melnyk, C. W. (2025). Water availability positions auxin response maxima to determine plant regeneration fates. Nature Plants, 1–13. https://doi.org/10.1038/s41477-025-02029-2
Photos
Photo collage (top image)
A cut leaf touching the media forming new roots (left) and a leaf with the cut site into the air forming callus (healing tissue) (right). Photo: Abdul Kareem (Adapted from Kareem et al., 2025, licensed under CC BY 4.0.)
Study of gene expression
