Auxin is plant hormone which is synthesized at the tip of the shoot. It helps the cell grow longer. When a tendril comes in contact with a support, auxin stimulates faster growth of the cells on the opposite side that’s why the tendril forms a coil around the support.

Tendril Are Also Known As Climbers. Auxin Hormone Is Present Around One Part Of Tendril & You Can Easily Know As One Part Of Tendril Shows Fast Growth 

How do auxins promote the growth of a tendril around the support?

Auxins are a class of plant hormones that play a crucial role in promoting the growth and development of various plant organs, including tendrils. Tendrils are specialized structures that plants use to climb and support themselves, and the growth of tendrils around a support is known as thigmotropism. Auxins are responsible for initiating and guiding this thigmotropic response in tendrils. Let's explore in detail how auxins promote the growth of a tendril around the support.

1. Initiation of tendril formation:
- Auxins are synthesized in the apical meristems of a plant and are transported towards the regions of growth.
- When a plant comes into contact with a support, auxins accumulate on the side of the tendril that is opposite to the support.
- This uneven distribution of auxins triggers the initiation of tendril formation on the side of the stem that is in contact with the support.

2. Differential growth:
- Auxins promote cell elongation and growth in plants.
- As the tendril starts to form, auxins accumulate on the side of the tendril that is in contact with the support.
- The higher concentration of auxins on this side stimulates cell elongation and growth, causing the tendril to curve around the support.

3. Cell wall modification:
- Auxins also influence the cell wall properties, making it more flexible and extensible.
- The higher concentration of auxins on the side of the tendril in contact with the support leads to the differential growth and elongation of cells in that region.
- The increased cell elongation and growth on one side of the tendril cause it to bend and wrap around the support.

4. Redistribution of auxins:
- As the tendril grows and wraps around the support, the distribution of auxins becomes more even.
- Auxins are transported away from the side in contact with the support and redistributed towards the opposite side of the tendril.
- This redistribution of auxins promotes further growth and elongation of cells on the side that is away from the support, allowing the tendril to continue curving and wrapping around the support.

In summary, auxins play a crucial role in promoting the growth of a tendril around a support by initiating tendril formation, promoting differential growth and elongation of cells, modifying cell wall properties, and redistributing auxins to facilitate further growth.