The laboratory of the Institute of Systematic Botany and Ecology houses a unique specimen: in the “Chinatron”, Germany’s only centrifuge of its kind, it is possible to do much more than just study how plants react to stress due to drought in times of climate change. The device also helps in developing “bionic branches”, which could be paving the way for new pumping and cooling systems.
Biologists like Steven Jansen, head of a research group at the Institute of Systematic Botany and Ecology, have been investigating water transport in plants for decades. Thanks to factors such as modern imaging procedures and analytical techniques, the anatomy of the tree trunk is for the most part already understood. However, engineers have not yet been able to develop a bionic branch that can convincingly imitate the waster transport of its model in nature. An artificial system such as this would help in developing pumps that could rid contaminated soil of chemicals. Applications in biomedicine and cooling technology are also a possibility. Researchers like Jansen would benefit as well: in the “bionic tree trunk”, they could more thoroughly investigate the water transport in plants and the formation of dangerous gas bubbles – an important topic, especially in the face of climate change. During periods of dryness, the sap in the vascular tissue (xylem) of the trunk is under immense soil-moisture tension as the tree attempts to extract water from the ground. In extreme droughts, the water column can even break, causing gas bubbles to appear and blocking any further flow of water. Such “embolisms” can mean certain death for a tree. The tendency to develop such blockages varies greatly between various plant species, and can be analysed within minutes in the new Chinatron.
How does a plant species react to dryness?
The device that is intended to pave the way for a deeper understanding of water transport and ultimately for an artificial tree trunk is actually rather plain: “Centrifuges have been used to investigate the formation of embolisms for many years. Based on the idea of biologist Hervé Cochard and developed in China, only two prototypes of the ‘Chinatron’ exist in Europe – and we have one of them in Ulm”, says Jansen. What makes the centrifuge so unique is the cuvette system. The natural or artificial branch is attached in the middle of the centrifugal axis. Both branch ends are inserted into plastic cuvettes filled with differing amounts of water. Holes are placed in these reservoirs in such a way that a drop in pressure occurs during centrifugation, enabling water flow in the branch from the upper to the lower cuvette. “In the Chinatron, strong centrifugal force acts on the sample at up to 10,000 rotations per minute, creating negative pressure in the trunk. While water is constantly being refilled into the lower cuvette, the level in the upper reservoir continues to drop. The system calculates the conduction velocity in the branch based on this difference”, explains research staff member Dr Christophe Trabi. Rotation and temperature can be changed by computer. Videos recordings from the centrifuge provide insight into the water transport and the formation of embolisms. With natural branches, it is possible to determine how a species reacts to dryness and an interruption of the water flow within about 30 minutes in the Chinatron.
Nature as a model
Developing and testing artificial branches in the Chinatron presents Professor Steven Jansen and his team of researchers with challenges. It is difficult to imitate the negative pressure in the trunk and the porous cell walls that connect the neighbouring vessels in the vascular tissue and provide resistance during water transport. These characteristics need to be imitated in tubes or glass fibres and tested in the Chinatron. The researcher team also hopes to explain the role of plant surfactants in the artificial system. Surfactants appear to reduce the surface tension of the water in the vascular tissue and thus lead to smaller gas bubbles and fewer embolisms. “We are probably the only group in the world who is conducting research on artificial branches. The Chinatron opens up many doors for us here”, says Jansen. The prototype, which cost 20,000 euros, was financed by the German Research Foundation (Deutsche Forschungsgemeinschaft: DFG) and is not only available to biologists. Other natural scientists such as chemists and experts from the fields of electron microscopy and stochastics have already worked with the device as well.
Text and Mediacontact: Annika Bingmann