Do plants sleep? The surprising science of sleep in the plant kingdom

Introduction

It is known that plants exhibit a circadian rhythm that is similar to the sleep and wake cycles of animals. With this knowledge, scientists are discovering similarities in plant and animal sleep processes to answer the question of whether plants sleep or not. This article will explore and explain the emerging evidence that plants sleep.

Circadian Rhythms

Plants have an endogenous clock that regulates daily to determine seasonal changes for flowering and leaf movements. Experiments are done to show that depriving plants of their day and night cycle can show disrupted biological rhythms, without these rhythms, it is hard for a plant to recognize its surroundings and to have a regular schedule for flowers to bloom. Gene homologs that control the circadian clocks of animals can also regulate the clocks of plants, further giving evidence that plants have a sleep schedule like animals. The use of these circadian rhythms is not only for detecting day and nights, they can also be used to adjust to environmental cues such as the length of one day and different temperatures, these rhythms help plants optimise functions and prepare for daily environmental changes.

Plant Sleep-Wake Behavior

The studies that have been conducted so far show similar postures between plants and animals, this includes drooping stems from plants as opposed to a slouching position for animals when they are sleeping upright. The patterns of growth that vary between plants have also shown resemblance to animal sleep-wake patterns, this includes having growth at night despite the lack of photosynthesis from the sun. Plants that have not been in the dark for long extended periods may absorb less light and disrupt their cycles, a trait of sleep deprivation in animals. The active transportation of nutrients within plants can vary depending on the daily cycle, changing and night to sleep which is another similarity to animal sleep processes.

Molecular Evidence for Plant Sleep

There is more surprising evidence that plants do sleep, the genes in plant homologs that regulate animal sleep, such as potassium channel genes, can control circadian rhythms and nightly processes in plants. Another piece of evidence may be the fact that a hormone called melatonin can often occur endogenously in plants. Plant cells also show signs of changing levels of calcium to signal gene expression at night resembling processes in animal sleep patterns. Epigenetic changes in gene expression and protein synthesis occur nightly in plant cells similar to animal sleep processes.


Functions of Plant Sleep

With justified evidence that plants do sleep, we can explore what purpose sleeping to plants. We know that animals and humans sleep to increase energy levels, it can also help improve brain functions for neurons to communicate with each other. Similar to animal sleep, plants rest to have an optimised resting time during the night for energy and to reduce energy use for maintenance during the dark. Plant sleep can also be a system where the plant naturally repairs itself from damage from sunlight that could have accumulated through the sunlight hours. The drooping leaves during sleep could theoretically protect the photosynthesis tissues inside the plant as there is no sunlight and can reduce the amount of water needed for the night. Conserving these types of energy is vital for animals and plants to thrive in their respective environment and could be used for increasing memory and to prepare for optimal functions throughout the day,




Conclusion



With such fascinating evidence of plants sleeping when compared with the postures and hormones sleep in animals, plants certainly sleep for various reasons such as conserving energy for the day to come, protecting the sensitive photosynthesis tissues, and improving memory, it is no secret that the sleeping behaviour of plants in vital for a plant to thrive alongside its circadian rhythm to fully operate and prepare for seasonal changes. With this knowledge, more and more scientists hope to use this sleep data for something more extraordinary; growing crops and plants on the moon, or even the red planet.


Citations
Brennan, M. (2019). Circadian rhythms in plants. Nature Plants, 5(8), 774-774. https://doi.org/10.1038/s41477-019-0490-2

Galland, P. (2018). The key elements of plant sleep. Science, 362(6419), 1046-1047. https://doi.org/10.1126/science.aav2617

Suzuki, E., & Mizuno, K. (2018). Molecular mechanisms underlying circadian clock-controlled behaviour in plants. Plant and Cell Physiology, 59(12), 2169-2179. https://doi.org/10.1093/pcp/pcy187