Chinese scientists discover new cell type, plants can move now!

The world we live in is colorful because of the existence of flowers, plants, trees and other plants. Like humans, flowers, plants and trees are also alive. And life lies in movement.

Can you imagine that plants that you usually see growing quietly also have their own way of moving? Recently, a study published in the journal National Science Review showed that plants can also move on their own, and their movement is related to the cell composition inside them .

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Contractile cells: new insights into plant movement behavior

Cells are the basic structural and functional units of organisms and the most fundamental part of maintaining life activities. Plant cells are generally composed of cell walls, cell membranes, organelles, and nuclei. Recently, Wang Yinzheng's research group at the Institute of Botany, Chinese Academy of Sciences, discovered a new type of cell, namely contractile cells filled with water-sensitive rough endoplasmic reticulum. Different from conventional cells, it directly determines the behavior of plants being able to move on their own .

Chirita pumila , also known as "variegated grass", is a plant belonging to the Gesneriaceae family. It has striped leaves and a strange appearance. It has a short growth cycle, a short plant, and can self-pollinate. Chirita pumila is often used for extensive research by botanists.

Variegated lip column moss, image source: Flickr, photo: Nicholas Turland

Plants generally cannot move autonomously, but in the process of studying the variegated lip column moss, botanists discovered that the stigma of the variegated lip column moss has the characteristic of spontaneous movement after contacting water.

In order to explore the reason, scientists dissected and analyzed the stigma of the variegated lip column moss. Under a microscope, they found that the stigma of the variegated lip column moss is composed of papillary cells, vascular bundles, thin-walled cells and dorsal epidermis. And their vascular bundles have up to 10 layers of cells, accounting for half of the thickness of the lamina.

There are obvious differences in the morphology of these cells when the stigma is in an open and closed state in contact with water. It can be seen that the nature of these cells is different from thin-walled cells, and botanists define them as contractile cells.

The open and closed states of the stigma of the variegated lip column

Characterization of the contracting cells using cryo-electron microscopy showed that these cells have a reticular structure inside and, unlike regular cells, the nucleus is at the edge of the cell rather than in the center.

(A) Stigma anatomy, (B) front view of stigma, the upper part of the stigma is closed, the lower part is open, and it opens outward at a 60° angle, (C) front view of closed stigma, (D) back view of stigma, (E) side view of stigma, (F) longitudinal anatomical sections of open and (G) closed stigma, (H) enlarged sections of open and (I) closed sections. Image source: Reference [1]

When the stigma absorbs water, the volume of the contracted cells will increase, and their morphology will be elongated more than 8 times compared to the initial state , indicating that there are water-sensitive substances inside the contracted cells. This swelling behavior after contact with water causes the cell volume to expand, which is closely related to the elongation and contraction movement of the stigma.

At the same time, further analysis of the cells with the help of electron microscopy and fluorescence experiments showed that the essence of the cell's reticular structure is the rough endoplasmic reticulum, and the ribosomes are embedded in the reticular structure. In addition, the experiment observed that when the stigma of the variegated lip column moss opens and closes, the contractile cells also move with it, which shows that the two are closely related.

Contractile cell structure, (A~H) cryo and transmission electron microscopy, (A~D) contractile cells and (E~H) thin-walled cells, fluorescence experimental characterization (I, J) thin-walled cells and (K, L) contractile cells, (M) cell fluorescence signal, (N~Q) stigma opening and closing movement. Image source: Reference [1]

There are actually many plants that can move!

There are far more plants that can move than the variegated column moss mentioned above. In fact, many common and familiar plants in our lives are also "athletes".

1

sunflower

"Growing towards the sun" is our common understanding of sunflowers. Since sunlight exposure directly affects the distribution of auxin inside the sunflower, which in turn affects cell growth, in order to better receive sunlight, sunflowers will move with the sun.

Sunflower. Copyrighted image from the photo library. Reproduction or use may result in copyright disputes.

2

Mimosa

When we touch the leaves of Mimosa, due to external stimulation, their petioles will droop and merge with the leaves. After a period of time, their leaves will open up again and return to their original state.

The reason for this movement is related to the cell structure of the upper and lower parts of their leaves. The cell walls of the upper part are thicker and the cells are denser, while the lower part is thinner and the cells are more sparsely distributed. Therefore, under external stimulation, the permeability of the cells in the lower part increases rapidly, and the leaves will droop and close.

Mimosa. Copyrighted image from the gallery. Reproduction may lead to copyright disputes.

3

Albizia Julibrissin

In addition to sunflowers and mimosas, the albizzia flowers that can be seen blooming everywhere in the park in June and July also move. During the day, the albizzia flowers will bloom freely in the grass, but will quietly close at night, which is related to their night sensitivity. When they sense changes in external light, they will move accordingly.

Albizia Julibrissin. Image source: Wikipedia

Conclusion

The world is so big and different life forms have their own unique features. Do the moving plants make your eyes light up?

Find a quiet afternoon, with warm sunshine and gentle breeze, and observe the quiet changes of these greens. Perhaps through observation, you can gradually enter the wonderful door of biological changes.

References

[1] Yin-Zheng Wang and others, A new type of cell related to organ movement for selfing in plants, National Science Review, Volume 10, Issue 9, September 2023, nwad208.

[2] Liu Bailing. Establishment of genetic transformation system of Chirita pumila[D]. University of Chinese Academy of Sciences, 2013.

[3] Sun Zhimin. Exploring the causes of plant movement[J]. Fossils, 1997(1):2. DOI:CNKI:SUN:HSZZ.0.1997-01-016.

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Produced by Science Popularization China

Author: Shi Wuyao, PhD in Biology

Producer丨China Science Expo

Editors: Lin Lin, Jin Yufen (Intern)

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