Anemotropism is about the interaction of plants with the wind. It feels so cool to watch the movement of plants in your garden in the breeze. It’s a scene we’ve all observed, right?
But have you ever wondered whether it’s merely the wind’s gentle touch? Or if the plants themselves are actively participating in this movement! Here comes the thought of anemotropism.
What is Anemotropism?
The term “Anemotropism” is derived from the Greek words “anemos” (meaning wind) and “tropism” (meaning turning). It refers to the ability of plants to respond and adapt to wind conditions.
The concept of anemotropism is similar to phototropism.
- Phototropism: Tropism to light (photon)
- Anemotropism: Tropism to the wind (anemos)
Adaptation of Plants to Wind
Plants have evolved remarkable strategies to adapt and thrive in wind. Their responses to wind are not just passive reactions. They represent a process of adaptations that enhance their chances of survival in the windy environment.
Here are some of the key ways in which plants have adapted to wind:
1. Swaying and Flexibility
Plants possess great flexibility to sway with the flow of the air. When it is breezing, and even if the wind is strong, plants tend to bend to the wind flow easily! But how do they do so?
Well, this flexibility in wind arises from specialized joint-like structures in plant stems known as pulvini. Pulvini is located at the base of leaves and stems.
These pulvini enable the plant to hold its position. That is why, plant leaves sway with the wind and return to their original position once the wind is stopped or slowed. This swaying motion not only slows down the energy of the wind but also reduces the risk of stem breakage.
2. Structural modification
In the face of persistent winds, certain plants undergo structural modifications to adapt. They tend to build shorter, sturdier stems with thicker cell walls. This adaptation is often called “wind-pruning“.
Wind pruning minimizes the risk of stem elongation and helps the plant maintain its stability. This feature is often found in the plants of windy coastal regions. They exhibit a characteristic bent or twisted growth pattern due to constant exposure to strong winds. This adaptive response to the wind is present in a wide range of plants.
3. Leaf Orientation for Water Conservation
Leaves are vital for photosynthesis, but they also play a crucial role in water regulation. Strong wind can intensify transpiration, leading to water loss through leaf stomata.
In response, some plants adjust the orientation of their leaves. They may angle or rotate them to reduce the surface area exposed to the wind. Twisted or curly or reduced leaves help plants avoid the effect of wind and minimize water loss.
For example, Agave plants, often found in arid regions, have long, narrow leaves. Sometimes they possess twisted or curly leaves to prevent water loss. This adaptive feature is particularly important for their survival in dry environments.
4. Seed Dispersal Strategy
Wind serves as a valuable partner in the seed dispersal strategies of many plant species. Some plants have evolved mechanisms to produce lightweight, tiny, and winged seeds. Such seeds are easily carried by the wind to new locations.
Dandelion seeds are a classic example of this strategy. As the seeds mature, the plant releases them. And they are carried away by the wind, increasing the plant’s chances of colonizing new areas.
Again, some plants produce winged seeds, e.g. maple trees (Acer spp.), ash trees (Fraxinus spp.), pine trees (Pinus spp.), Dipterocarpus spp., etc. These seeds have wings or wing-like structures attached to the seeds which help in their dispersal by wind.
5. Mechanical Response
Plants can receive chemical signals to prepare for and respond to wind stress. They produce specific signaling molecules that trigger physiological changes.
We will now deep dive into how plants receive, use, and respond to signals of the wind.
Chemical signaling of plants
Plants have developed complex signaling systems to sense and respond to various environmental stimuli, including wind. In the context of wind-induced stress, plants possess chemical signaling mechanisms to initiate adaptive responses.
Here are some key scientific insights into this process:
1. Signaling Molecules
Plants can produce specific signaling molecules in response to mechanical stress caused by wind. These molecules often include phytohormones such as abscisic acid and jasmonic acid.For example, abscisic acid plays a central role in stress responses and helps coordinate various adaptive changes in the plant.
There are special proteins involved in perceiving mechanical stress in plants. This proteins are known as Mechano-proteins or mechano-receptors. They are found in plant cell membranes.
Mechanoproteins transmit signals in response to changes in cell shape or tension. When these proteins detect any mechanical stress in plants, they trigger a series of biochemical events that lead to the production of signaling molecules.
3. Transduction Pathways
Once the mechanical stress is detected, signal transduction pathways are activated. These pathways involve a series of biochemical reactions, including the activation of enzymes and the release of secondary messengers. These events ultimately lead to the activation of specific genes and the initiation of stress responses.
Response to chemical signals by plants, produced during stress
Plants show various changes in response to mechanical stress produced by environmental factors, e.g. wind. These changes include the reinforcement of plant cell walls and structures. This reinforcement is critical for withstanding mechanical stress and maintaining the plant’s integrity.
Here’s a brief view of how the reinforcement of plant cell walls and structures takes place:
1. Cell Wall Modification
Chemical signaling, particularly through the action of phytohormones like abscisic acid and jasmonic acid, leads plants to modifications in the composition and structure of plant cell walls.
These modifications often involve the deposition of additional material, such as lignin and cellulose, in the cell walls. This strengthens the walls, making them more rigid and resistant to bending or breaking.
2. Cell Wall Cross-Linking
Cross-linking in a cell wall refers to the process of forming chemical bonds, known as “cross-links,” between different molecules within the cell wall structure. These bonds create connections or links that strengthen the overall integrity and rigidity of the cell wall. As a result, the cells become more resistant to mechanical stresses and environmental challenges.
The process of cell wall cross-linking involves the action of enzymes like peroxidases, laccases, etc., and chemical compounds that act as cross-linking agents. These agents collectively catalyze the oxidative coupling of lignin polymers. This results in the formation of new chemical bonds, often referred to as “cross-links,” between adjacent lignin molecules or between lignin and other polysaccharides like hemicellulose.
These newly formed bonds strengthen the overall structure of the cell wall.
3. Strengthening of Plant stems
Beyond the cell walls, chemical signaling can also affect the strengthening of other plant structures. This includes the reinforcement of stems, branches, and leaves to withstand mechanical forces exerted by the wind. Enhanced structural integrity helps prevent damage and breakage in different plant parts.
4. Gene Expression Regulation
Chemical signaling not only influences cell wall reinforcement but also regulates the expression of genes involved in stress responses. This can lead to the synthesis of proteins that contribute to enhanced mechanical strength and resilience in windy conditions.
Research papers related to this topic:
- Grass Cell Walls: A Story of Cross-Linking by Ronald Hatfield, David M. Rancour, and Jane Marita.
- Chemical signaling under abiotic stress environment in plants by Narendra Tuteja &Sudhir K. Sopory.
- Sensor types in signal transduction pathways in plant cells responding to abiotic stressors: do they depend on stress intensity? by Alina Kacperska.
- Challenges to understand plant responses to wind by Yusuke Onoda &Niels P.R. Anten.