Scientists discover new way to transport liquid in succulent plants

Produced by: Science Popularization China

Author: Shi Chang (PhD in Physical Chemistry)

Producer: China Science Expo

Editor's note: In order to understand the latest developments in cutting-edge science and technology, the China Science Popularization Frontier Science Project has launched a series of articles titled "Understanding Top Science Journals", which selects outstanding papers from authoritative journals and interprets them in plain language as soon as possible. Let us broaden our scientific horizons and enjoy the fun of science through the window of top journals.

The transmission of fluids provides the necessary water and nutrients for the survival and growth of plants and animals, and is an indispensable part of the normal functioning of living organisms. Blood circulates in the body through a network of blood vessels, providing oxygen and nutrients to cells, and excreting carbon dioxide and waste produced by cell metabolism, maintaining the stability of the life system.

Plants generate pulling force through transpiration of leaves, driving roots to continuously absorb water from the soil and transport it to the parts that need water through the duct system, thus maintaining the water balance of the plant body. Spider silk can capture droplets or dew in the air and transport water to the joints through the periodic spindle knots on its surface.

Spider web with water drops

(Photo source: veer photo gallery)

In animals and plants, the transport of liquids is usually unidirectional and along a fixed direction. So are there liquid pathways that can selectively transport liquids in any direction?

On June 20, 2024, Chinese scientists published an article in the journal Science on the selective directional liquid transport in the leaves of the succulent plant Ruolu, revealing a new liquid transport mode in nature.

The research results were published in the journal Science

(Image source: Reference 1)

What kind of plant is Ruolv? What are the characteristics of its liquid transmission?

Ruolu is a succulent plant of the Crassulaceae family and the genus Sedum. It is native to South Africa and Namibia and is known for its fast growth rate and strong adaptability. Ruolu has a peculiar appearance, with small leaves arranged in a scattered manner. In addition to its vertical distribution, its branches are also distributed horizontally and obliquely, which is unique among succulents.

There is another reason why the plant is so popular among gardening enthusiasts: its leaves can change color. When the sun is sufficient, the top leaves of the plant will turn red, adding a touch of brightness to the monotonous plant.

Succulents

(Photo source: veer photo gallery)

Ruolu has great ornamental value and attracts many succulent plant lovers. Chinese scientists also have such a pot of Ruolu, but this pot of Ruolu is different because it helps its "fellows" reveal their own "secrets".

When watering the Ruolu plant, the researchers found that the liquid on the horizontally distributed stem of the Ruolu plant could actually selectively flow in two opposite directions: toward the stem tip or the root. This selective liquid transmission method is different from the traditional liquid transmission method and has important research significance.

How is selective liquid delivery mode achieved?

The mechanism of selective directional liquid transport of Ruolu is hidden in its unique leaf structure. The researchers used ethanol as the liquid and dropped it on two different groups of Ruolu stems to conduct liquid transport experiments. The results showed that the direction of liquid transport on the stems of Ruolu is related to the concave tilt angle of the leaves. Ruolu leaves have an asymmetric concave structure, that is, the direction towards the stem tip presents an upward-tilted concave angle, and the direction towards the root presents a downward-tilted concave angle.

When the upper inclination angle was 32°±8.5° and the lower inclination angle was 37°±6.6°, ethanol spread unidirectionally toward the stem tip, and the reverse direction was effectively blocked. When the upper inclination angle was 55°±5.2° and the lower inclination angle was 34°±4.8°, ethanol spread unidirectionally toward the root.

The researchers also used 3D printing technology to prepare array devices that resemble green leaf structures, verified the theoretical model of the anisotropic curved liquid surface, and revealed the key role of the tilted concave angle in controlling the direction of liquid transport.

A. The concave angle of a green leaf; B. The water transfer to the tip of a green leaf; C. The water transfer to the root of a green leaf; D. The relationship between the distance and time of liquid transport; E. Comparison of liquid transport methods on different surfaces

(Image source: Reference 1)

Applications of selective and directional liquid transport

Based on the asymmetric concave angle structure of the leaves of the Ruolu succulent, the researchers designed a series of bionic devices. For example, by introducing magnetic NdFeB materials as fillers, the tilted concave angle of the imitation leaf structure is changed under the action of an external magnetic field to achieve selective transport of liquids. The spacing of the imitation leaf structure is changed through mechanical stimulation to achieve switching of the liquid transport direction.

If the selective directional liquid transport capability of green succulent leaves is revealed, we can hope to achieve the reconfigurability of liquid transport and the intelligent control of the transport direction, and further realize autonomous, long-distance directional liquid transport. This capability has shown extremely broad and attractive application potential in many fields such as biomedical testing, chemical reaction analysis, and microfluidics.

AC. Diagram of the transmission path of liquid in different green leaf devices

(Image source: Reference 1)

Conclusion

The progress of science and technology often comes from life. Scientists use their keen insight to capture inspiration from the subtleties of daily life, extract the subtle laws of nature, and then transform them into high-tech products that promote social progress. Exploration never stops, and discovering is infinite. It is this curiosity and unremitting pursuit of the unknown world that leads us to appreciate the infinite wisdom given by nature. We look forward to more natural laws being revealed and technology lighting up the future.

References

1.Yang L, Li W, Lian JY, et al. Selective directional liquid transport on shoot surfaces of Crassula muscosa[J].Science,2024.

2.Parker AR , Lawrence CR .Water capture by a desert beetle[J].Nature, 2001.

3. Chen Zhen, Zhang Zengzhi, Du Hongmei, et al. Research status of application of bionic materials in water harvesting[J]. Materials Engineering, 2020.

4. Jiang Chao, Han Peng, Qi Guicun, et al. Research progress of bionic water-harvesting materials and technologies[J]. Petrochemical Engineering, 2021.