Seventy-four detailed microscopic images combined to create a full image of a thale cress leaf have won third prize in the Danish National Research Foundation’s photo competition 2018. The image is part of the research carried out at the DynaMo Center and visualizes the plant’s internal transport highways – a system that researchers are seeking to decode to create better crops for the future.
On a pitch-black background we see the contour of a green leaf with yellow-green structures outlining an internal network. This final image was created by compiling 74 very detailed images taken with a microscopy technique called CLSM. Each image makes it possible for researchers to study small internal sections of the leaf at a microscopic level. The photograph recently won third prize in the Danish National Research Foundation’s photo competition 2018, for which the foundation’s grantees had the opportunity to submit fascinating photos from the world of basic research.
“Normally, the leaf is so thick that we can’t see this internal network with the naked eye. What we have done to make it visible is to combine a clearing process with the binding of a fluorescent protein – a protein that is able to absorb light and fluoresce – to specific transporter proteins. When we illuminate the leaf with light with specific wavelengths, the fluorescent protein bound to the transporter protein will absorb the light and fluoresce. This will visualize where the transporter proteins are located within the leaf, and thereby the leaf’s transport network will show,” explained Pascal Hunziker, creator of the winning photo and a Ph.D. student at the DNRF Center for Dynamic Molecular Interactions (DynaMo) at the University of Copenhagen.
The leaf is coming from the plant thale cress, which has been used as a model system in plant biology for a long time because of the plant’s genetic and molecular properties. Thale cress is also used as a model system at the DynaMo Center, where the researchers focus on the plant’s defense compounds – glucosinolates – to understand molecular processes at the cellular, tissue, and organismal levels. This is exactly the reason why the researchers are interested in the leaf’s internal transport network.
Transporter proteins move defense compounds around in the plant
In addition to carrying nutrients through the plant, the transport network also serves to move defense compounds around.
“The proteins, which light up in the image, import the glucosinolate defense compounds onto the transport network. The glucosinolate defense compounds are part of a mustard bomb. When an insect chews on the leaf, the glucosinolates are hydrolyzed and toxic compounds are released, which will deter the insect from eating the leaf,” said Hunziker.
The transporter proteins that fluoresce in the leaf of the thale cress plant and thereby map the transport network were actually discovered by researchers from DynaMo, including head of center Barbara Halkier, and made public in the scientific journal Nature in 2012.
DynaMo scientists keep defense compounds out of seeds
In addition to mapping the transport network in the plant, the discovery of the transporter proteins also enables the scientists to apply this knowledge to alter the distribution of the glucosinolate defense compounds in the plant, e.g., by keeping the toxic defense compounds out of the seeds, but maintaining them in the rest of the plant so that it can defend itself.
“When we have the knowledge of proteins such as these and understand their role, it is possible to breed plants with a reduced level of toxic defense compounds in the seeds and thereby increase the nutritional value for the benefit of agriculture and food production in the future,” explained Hunziker.
For instance, thale cress is related to the mustard plant, which produces the bitter defense compounds that give mustard its distinctive flavor. Researchers at the DynaMo Center are currently working on creating a mustard plant in which the plant’s toxic defense compounds are reduced in the seeds, but still present in other parts of the plant.
Such a mustard plant without the toxic defense compounds in its seeds has the potential to become a future source of plant oil, biodiesel fuel, and animal feed. The mustard plant is far more resistant to heat, drought, and diseases than the rapeseed plant, which today is one of the world’s most important oilseed crops, but its growth is being challenged by climate change.
The center environment attracted Hunziker
Significant research results, such as the discovery of the transport proteins in thale cress and the development of transport-based technologies that can improve crop plants, have made the DynaMo Center a global leader in its field. In its work with the mustard plant, the center collaborates with one of the world’s largest players in agricultural biotechnology, Bayer Crop Science. And the center’s reputation and stimulating environment were exactly what attracted Hunziker, who is from Switzerland, to Denmark.
“I applied for the position at the center because of the great possibilities it could offer, and came here in 2015. The size of the center and the research groups was a major part of my motivation to come here,” explained Hunziker. He added:
“The stimulating environment at DynaMo was especially attractive as one has the opportunity to interact and work with a lot of different people who have a wide variety of backgrounds in the world of research.”