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Biology LibreTexts

30.7G: Plant Responses to Wind and Touch

  • Page ID
    13771
  • Plants respond to wind and touch by changing their direction of growth, movement, and shape.

    LEARNING OBJECTIVES

    Compare the ways plants respond to directional and non-directional stimuli

    KEY TAKEAWAYS

    Key Points

    • When subjected to constant directional pressure, such as a trellis, plants move to grow around the object providing the pressure; this process is known as thigmotropism.
    • Thigmonastic responses include opening and closing leaves, petals, or other parts of the plant as a reaction to touch.
    • Through thigmomorphogenesis, plants change their growth in response to repeated mechanical stress from wind, rain, or other living things.

    Key Terms

    • thigmotropism: plant growth or motion in response to touch
    • thigmomorphogenesis: the response by plants to mechanical sensation (touch) by altering their growth patterns
    • thigmonastic response: a touch response independent of the direction of stimulus

    Plant Responses to Wind and Touch

    The shoot of a pea plant wraps around a trellis while a tree grows on an angle in response to strong prevailing winds. These are examples of how plants respond to touch or wind.

    The movement of a plant subjected to constant directional pressure is called thigmotropism, from the Greek words thigma meaning “touch,” and tropism, implying “direction.” Tendrils are one example of this. A tendril is a specialized stem, leaf, or petiole with a threadlike shape that is used by climbing plants for support.The meristematic region of tendrils is very touch sensitive; light touch will evoke a quick coiling response. Cells in contact with a support surface contract, whereas cells on the opposite side of the support expand. Application of jasmonic acid is sufficient to trigger tendril coiling without a mechanical stimulus.

    image

    Thigmotropism in a redvine: Tendrils of a redvine produce auxin in response to touching a support stick and then transfer the auxin to non-touching cells. The non-touching cells elongate faster to curl around the support stick.

    A thigmonastic response is a touch response independent of the direction of stimulus. In the Venus flytrap, two modified leaves are joined at a hinge and lined with thin, fork-like tines along the outer edges. Tiny hairs are located inside the trap. When an insect brushes against these trigger hairs, touching two or more of them in succession, the leaves close quickly, trapping the prey. Glands on the leaf surface secrete enzymes that slowly digest the insect. The released nutrients are absorbed by the leaves, which reopen for the next meal.

    Thigmomorphogenesis is a slow developmental change in the shape of a plant subjected to continuous mechanical stress. When trees bend in the wind, for example, growth is usually stunted and the trunk thickens. Strengthening tissue, especially xylem, is produced to add stiffness to resist the wind’s force. Researchers hypothesize that mechanical strain from wind, rain, or movement by other living things induces growth and differentiation to strengthen the tissues. Ethylene and jasmonate are likely involved in thigmomorphogenesis.

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