Do plants and trees sleep?

All animals sleep. Human beings also sleep at night usually. Sleep is the period of rest. It is controlled by Central Nervous System.  After a hard day’s work, human beings and other animals go to sleep because they need to rejuvenate their body and mind.

During sleep. The body is at rest. But vital organs perform their functions. For example, our heart pumps blood, we inhale and exhale through our lungs, kidneys eliminate waste material from our body and our brain is active. That means all our vital organs perform their duties at optimum level.

Human beings sleep at night because of the secretion of a hormone called melatonin by the pineal gland, in the brain. The production and the release of this hormone occurs with a daily rhythm.  The secretion of this hormone is maximum during night. This secretion is carried to all the cells of the body through blood. The main function of this hormone is to signal the body that it is night and to assist our body to go to sleep.

Plants do not have a Central Nervous System or brain. All the plants and trees are busy during the day because of Photosynthesis. During night time, photosynthesis cannot take place as sun is absent. Sunlight is the key triggering element of all the activities of all living things. All living things including plant life follow circadian rhythm.

What activities are carried by plant during night time? Do they sleep? Do they rest? Are there any hormones produced in the plant body to put them to sleep like situation?

When sunlight dims, the plants stop the manufacture of glucose. But they start delivering the stored glucose to all the parts of the plant.  Light and dark stimulate the production of the hormone Auxin which is responsible for the growth of plants.  We have seen that in many plants, flowers bloom during the day and leaves close during the night.

 A study was undertaken by the scientists in Austria, Hungary and Finland. They developed laser scanners to study the day and night rhythm of trees and plants. The laser scanners enabled the scientists to build a complete 3D images of plants and trees.

They measured the lengths of plants and trees during day as well as during night. They found that the trees and plants measured little less during night and the leaves and branches were drooping. The drooping  of leaves and branches was of 10cms in trees measuring 5mts. The leaves and the branches were shown to droop gradually during the course of night. The lowest position reached a couple of hours before sunrise. In the morning, the trees returned to their original position within a few hours. 

Their temporary conclusions are as follows:

During the day time, photosynthesis take place in plants and trees. A force called turgor pressure build up in the leaves. Therefore the leaves and plants are steady and focused towards sunlight.

During night time the sun is absent. No photosynthesis take place.  The leaves of trees and plants start drooping down. The turgor pressure of leaves drops as plants are not photosynthesizing.

Scientists are not clear about certain things like the plants coming back to its normal position as the sun rises is waking up from sleep or normal internal rhythm of the trees and plants.

Research is required in this aspect of plant life to understand their behavior.