Plants do not have emotions or the ability to panic as humans or animals do. However, plants do exhibit certain behaviors in response to rain or water. This response is due to their ability to sense and adapt to environmental changes.
An international team of scientists involving The University of Western Australia's School of Molecular Sciences, the ARC Centre of Excellence in Plant Energy Biology, and Lund University has made the surprising discovery that a plant's reaction to rain is close to one of panic.
Rain Triggers Chemical Signals in Plants
The research, published in Proceedings of the National Academy of Sciences, revealed complex chemical signals are triggered when water lands on a plant to help it prepare for the dangers of rain. UWA Professor Harvey Millar said after spraying plants with water and observing the effect, the researchers noticed a chain reaction in the plant caused by a protein called Myc2.
"When Myc2 is activated, thousands of genes spring into action preparing the plant's defenses."
Protective Effects on Plant Panic During Rain
Professor Millar explains that these warning signals travel from leaf to leaf and induce a range of protective effects. As to why plants would need to panic when it rains, strange as it sounds, rain is actually the leading cause of disease spreading between plants.
"When a raindrop splashes across a leaf, tiny droplets of water ricochet in all directions. These droplets can contain bacteria, viruses, or fungal spores. A single droplet can spread these up to 10 meters to surrounding plants."
The researchers used a spray bottle to simulate rain. They found that, after 10 minutes, over 700 genes in the plants they studied reacted in a “panic-like” manner and continued to do so for about 15 minutes. The response was rapid, even from just a single touch of water, these scientists said. The response affected chemical reactions in the plants, such as their hormone balance and how they create proteins. Warning signals were sent from leaf to leaf in the plants, with the plants ultimately taking defensive measures against the water. Plants that received repeated waterings had stunted growth and delayed flowering.
Plants Are Communicating
One of the most interesting reactions involved the plants “communicating” their fears or stress with other nearby plants. They communicate via the release of airborne chemicals that can travel to other plants. As Millar said:
"If a plant’s neighbors have their defense mechanisms turned on, they are less likely to spread disease so it’s in their best interest for plants to spread the warning to nearby plants."
Evidence also suggests that when it rains, the same signals spreading across leaves are transmitted to nearby plants through the air.
Positive Effects of Rain on Plants
- Hydration: Rain provides water, which is essential for plant growth and survival. It hydrates the roots, stems, and leaves, allowing them to carry out necessary metabolic processes.
- Nutrient distribution: Rainwater helps to dissolve and distribute nutrients in the soil, making them more readily available for plants to absorb through their roots.
- Soil aeration: Rainwater can loosen compacted soil, which allows for better air circulation and water penetration, leading to healthier root systems.
- Cleansing: Rain can wash away dust and pollutants from plant surfaces, allowing for more efficient photosynthesis.
Negative Effects of Rain on Plants
- Overwatering: Excessive rain can cause waterlogged soil, which leads to a lack of oxygen and potential root rot. This can be harmful or even fatal to plants.
- Erosion: Heavy rainfall can cause soil erosion, leading to a loss of valuable topsoil and nutrients.
- Disease: Wet conditions can create an environment conducive to the growth of fungi and other pathogens, which can lead to various plant diseases.
- Physical damage: Heavy rain or hail can cause physical damage to plants, breaking stems, and leaves or damaging flowers and fruits.
Bottom line: Even though plants need water, new research shows that they panic about getting wet and can communicate about this and other perceived dangers. So, they do actually react to changes in their environment. Rain can have both positive and negative effects on plants, depending on factors such as the amount of rainfall, duration, and other environmental conditions.