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Tendril

life science Maturity 11-13 Next article →

A tendril is a specialized plant organ used for climbing and attachment. These thread-like structures allow plants to find support and reach higher into the canopy. Reaching the canopy helps plants access more sunlight resources. Tendrils can grow from several different parts of a plant. They may develop from stems, leaves, or inflorescences, which are clusters of flowers.

Vine
Vine

Because they come from different origins, scientists have identified 17 different types of tendrils based on how they grow and where they start.

The process of finding support begins with a movement called circumnutation. This is a circular, oscillatory pattern where the tendril grows and moves around its own axis. This constant motion increases the chance that the tendril will contact a physical structure. Research from 2019 shows that tendrils can sense their environment during this stage. Without a support to grab, tendrils will circumnutate toward a light stimulus. However, if a support stimulus is present, the tendril changes its direction to move toward that support.

Tendril of climbing plant
Tendril of climbing plant

Once a tendril touches an object, it uses a process called thigmotropism to coil. Thigmotropism is the way a plant responds to physical touch. In garden peas, sensitive cells on the cell walls initiate a signal, often as a calcium wave. This starts a signaling cascade involving phytohormones, which are plant hormones. Two important hormones in this process are gamma-Aminobutyric acid (GABA) and Jasmonate (JA). These signals activate a protein pump called plasma membrane H+-ATPase. This pump moves hydrogen ions from inside the cell to the apoplast, which is the space outside the cell membrane. This movement creates an osmotic gradient that leads to a loss of turgor pressure. The resulting difference in cell size causes the tendril to curl tightly around the object.

Vine
Vine

Tendrils vary significantly in their physical structure and size. For example, the plant *Nepenthes harryana* can have tendrils reaching 27 inches long. The chestnut vine, *Tetrastigma voinierianum*, has tendrils up to 20.5 inches. Most plants have only one simple or branched tendril at each node, which is a point on the stem. However, the aardvark cucumber, *Cucumis humifructus*, is an exception and can have up to eight tendrils at a single node. Some plants even use tendrils to support other structures. In *Nepenthes* plants, the tendrils support the specialized pitcher traps used for catching food.

Different plant species use different parts of their anatomy to create these tools. In the garden pea, only the terminal leaflets are modified into tendrils. In the yellow vetch, the entire leaf becomes a tendril, while the stipules take over the job of photosynthesis. Members of the *Clematis* genus use the rachis, or the main axis of a compound leaf, as a tendril. Even common fruits show this variety. Watermelon tendrils come from modified stems, while grapevines use modified inflorescences.

Tendril of climbing plant
Tendril of climbing plant

Charles Darwin provided the first comprehensive study of these movements in 1865. His monograph, *On the Movements and Habits of Climbing Plants*, was a landmark in botany. Darwin coined the term circumnutation to describe the searching motion of growing stems. He also discovered a phenomenon called tendril perversion. This occurs when a tendril forms two sections of counter-twisted helices with a transition in the middle. His work helped scientists understand how plants actively interact with their physical surroundings.

Plants also use a sophisticated method called self-discrimination to choose their supports. They use chemoreception, or the sensing of chemicals, to avoid climbing their own species. When a tendril touches a neighboring plant of the same species, specific signaling molecules bind to its chemoreceptors. This prevents the thigmotropic pathway from starting, so the plant does not coil. This is seen in the plant *Cayratia japonica*. Researchers found that if they coated a stick with oxalate crystals from *C. japonica* leaves, the tendrils would not coil around it. This ability helps plants avoid competition for resources and ensures they climb more stable, rigid structures.

Vine
Vine
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