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

The growth of a tendril around a support is a process known as thigmotropism, and auxins play a crucial role in this response. Thigmotropism is a type of tropism, which refers to the growth or movement of a plant in response to touch or contact with a solid object. In the case of a tendril, which is a slender, spirally coiling structure, thigmotropism allows it to wrap around a support structure for stability and climbing.

1. Touch Perception:

» When the tendril comes into contact with a solid object, such as a support structure, it perceives the touch or mechanical stimulus.

2. Auxin Redistribution:

» Auxins, particularly indole-3-acetic acid (IAA), are the primary plant hormones involved in tropic responses. Upon sensing touch, there is a redistribution of auxins within the cells of the tendril.

3. Asymmetric Auxin Distribution:

» The contact or touch leads to an asymmetric distribution of auxins, with higher concentrations on the side of the tendril away from the support.

4. Cell Elongation and Curling:

» Higher concentrations of auxins stimulate cell elongation on the side of the tendril facing away from the support. This differential cell elongation causes the tendril to curve and wrap around the support.

5. Coiling and Growth Response:

» The asymmetric growth and elongation of cells result in the tendril coiling around the support. This coiling is a growth response driven by the differential distribution of auxins.

6. Tendril Attachment:

» As the tendril continues to grow and coil, it eventually wraps around the support structure, providing the plant with a means of attachment for climbing.
The process described above allows the plant to efficiently utilize external structures for support and climbing. Thigmotropism, facilitated by auxins, is a mechanism that enhances the plant’s ability to reach sunlight, reduce competition for resources, and optimize its position in the environment.

In summary, auxins promote tendril growth around a support by inducing differential cell elongation in response to touch, leading to the tendril coiling and attaching to the support structure.