Circadian clocks, keeping the rhythm of life

The circadian clock regulates the daily and yearly schedule of a plant. These clocks help to regulate biochemical and developmental processes throughout a plant’s lifetime. Circadian rhythms are known as daily cycles. If you had to plot the cycle's rhythm it would look a lot like a heartbeat. These rhythms control important processes such as photosynthesis, development, and gene expression.

What does circadian rhythm mean for plants?

The circadian rhythm/cycle helps plants to perceive the season. This ability allows plants to choose the best time to perform certain processes. For instance, circadian rhythms help plants to flower at the best time for their pollinators. Due to the spring-time abundance of bees and butterflies, flowering occurs in this season in many plant species. Another example would be of trees starting to drop their leaves before winter as this helps them to save energy for surviving the cruel winter ahead. There are several such plant growth behaviors that occur due to circadian rhythms.

Did you know every cell has its own circadian clock?

Imagine if doctors in hospitals were only working when the banks were open. Serious issues would arise. This is why these departments have their own operating hours. Similarly, plants need their departments running independently as well.

In a plant, each tissue has its own unique function. Therefore, they operate independently. As a result, each type of tissue has its own circadian clock and every cell in the tissue is able to self-regulate its clock. Thus, the circadian clock of a particular tissue consists of clocks of many cells which results in better functioning of the entire plant.

An ever-changing clock

The fundamental reality of life is to adapt to changing environment. A plant’s ability to adapt to the environment is crucial, as it cannot move to favorable climatic conditions. The circadian clock adapts its rhythms to the conditions at hand. Plants have the ability to change their daily, monthly, and yearly cycles to best suit their needs. The cycles can be altered in such a way that favorable genes are expressed at the best times. For instance, flowering or fruiting can be delayed until the weather conditions are good. This would not be possible without the dynamic nature of circadian clocks.

How is plant tissue culture used to study circadian clocks?

Plant tissue culture has a key role in studying the circadian clocks of different plant species. This method allows cells and tissues to be studied independently. For instance, tissue culture allows scientists to study different tissue growth cycles. Cultures can be grown for various types of tissues including meristematic, embryonic, and mature tissues.

What about single plant cells? Well, plant tissue culture can solve that too. Cell suspension culture is the answer. This can generate complete plants using single plant cells in a liquid medium. This method is helpful for scientists to study circadian rhythms at cellular levels. You can read more on this method in our article on 'Cell suspension culture: an overview'.

Tissue rhythmicity persists even after removal from the plant. For example, leaf tissue culture shows the same photosynthetic rhythm as the plant from which it was taken. This shows that the circadian clock in tissue culture provides a good model to study the clocks in different plant species. Yet another reason for plant tissue culture’s increasing popularity.

Are circadian clocks and photoperiodism the same?

Not quite. However, strong similarities do exist. Circadian clocks are entertained by light, temperature, and other environmental signals. Photoperiodism is the response to the length of the day that enables plants to adapt to diurnal and seasonal changes. Therefore, photoperiodism is a mechanism of these clocks, as it involves light. If photoperiodism interests you, then read our article on  ‘Photoperiodism, the clock of production.’ Light controls many circadian cycles. Temperature changes alter the clock to prepare for winter. While soil characteristics can affect the rates of certain plant processes such as growth and maturation.

The effects of light and temperature have been shown to affect the daily transport of solutes (e.g., sugars and hormones) in a plant. When a plant senses a daily decrease in light and temperature the clock adjusts to store more solutes in the roots. This prepares the plant for winter. This process reverses during the summer season.

How can we make more beer with different circadian rhythms?

Barley is an important ingredient in many beers. It is also an interesting plant to study circadian rhythms.

Researchers studied the circadian rhythms of wild barley populations grown in different ecogeographic regions and found three important attributes: phase, period and amplitude. Wild barley was chosen because of its high genetic diversity and these attributes were used to compare differences in their circadian rhythms.

The results showed that wild barley populations from different regions expressed different rhythms, with circadian periods. While soil compositions correlate with circadian amplitudes. Circadian amplitudes simply mean the rates of a process. Thus, a large circadian amplitude equals a high rate. For example, a large circadian amplitude related to photosynthesis relates to a high amount of sugar being produced per second. Although, other factors may also have a role in the amplitude differences. Challenging environments select plants with high amplitude rhythms. Meaning they are more likely to survive and reproduce in harsh conditions.

How does this fill your beer mug though? Wild barley populations with high amplitude rhythms can be crossbred with other populations to create favorable hybrids. The product is a more stress-tolerant barley crop. This results in cheaper barley for beer brewing.

We hope this article will be useful for many of you to understand the concept of circadian clocks in plants. For more articles like this, keep checking our space!

By Christos Tripodis | 2-November-2021

About the author

Christos Tripodis was raised in the windy city of Port Elizabeth, South Africa. This southern coastal city is now known as Gqebreha and is the Bottlenose Dolphin Capital of the World. During his time at Nelson Mandela University, Christos focused on physics and biology. Eventually graduating with a BSc Honours in Botany with a focus in ecophysiology and phytoremediation. Currently, Christos is using his communication skills and understanding of botany as an Inside Sales Representative at Lab Associates B.V. When he is not reading or writing you can find him botanizing or in the ocean. His other passions include cooking, martial arts, and languages.


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