Glacier FarmMedia – Have you ever had a bad case of jet lag, when you get off a long flight and your body is telling you it’s time to sleep, but the outside world is telling you it’s time for breakfast?
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Plant roots have their own thermometer to measure the temperature of the soil around them and they adjust their growth…
That’s the biological effect of the inner body clock, also known as the circadian clock.
Plants, fungi and even some bacteria have circadian rhythms too.
Although plants don’t hop onto international flights, any living organism with a circadian clock has the potential to get jet lagged. This information could be used to make crops more productive and tackle food security.
The first reports of an inner body clock in plants stretch back to ancient Greece, when a ship’s captain studied the daily opening and closing of leaves on a tamarind tree. The first systematic observations of plant circadian rhythms were conducted in the 1700s by French scientist Jean-Jacques d’Ortous de Mairan, who studied the similar leaf opening and closing of Mimosa pudica, a plant in the pea family.
De Mairan noticed these cycles persisted even when the plant was in constant darkness. Thus, the leaf movements were not a response to changes in light conditions, but were controlled by the plant itself. This is the definition of a circadian rhythm.
We now know these rhythms are controlled by a genetic network found inside each plant cell. About 20 genes control the circadian rhythm in plants. These genes switch each other on and off in a complicated circuit, generating a 24-hour rhythm.
This circuit also activates other genes. Some are activated at dawn, followed by others later in the morning, but which are switched off by afternoon. For example, genes associated with photosynthesis are typically activated in the morning to make the most of the daylight, while genes associated with growth and development are normally active at night.
Lab experiments demonstrate that if any circadian control genes are mutated, the plant’s clock may speed up to give a shorter rhythm, slow down to give a long cycle or stop functioning altogether.
Plants with mutated circadian genes have faster or slower clocks and but their ability to photosynthesize, grow and reproduce is damaged. A plant with an out-of-kilter clock may only grow to half the size of a normal plant under laboratory conditions.
Almost every process that scientists have looked at in plants is regulated by the internal clock to some extent. It controls opening and closing of the stomata pores on the underside of a leaf, gas exchange in photosynthesis, shoot and root growth, seasonal flowering and “chemical warfare,” when some plants produce chemicals toxic to animals looking to eat them.
While most of the research into plant circadian rhythms has been limited to the lab, there is increasing interest in how it might be applied to agriculture.
The knowledge could help increase crop yield or control the flowering window to adapt to climate change.
Natural alterations in clock genes have been associated with farming breakthroughs. For example, tomatoes were originally farmed in central America where day lengths don’t change much through the year.
As people started growing them farther north, they inadvertently selected a variety with a natural mutation, which resulted in a slower clock. The tomato plants were able to make better use of the longer summer days and photosynthesize for longer.
Spring and winter cereals flower at different times of year due to a genetic difference in a circadian clock-associated gene. Farmers therefore sow different genetic varieties of the same crop in particular seasons to maximize productivity.
With the development of indoor vertical farming, there is huge interest in understanding plant circadian responses to light, so that lighting systems can be designed to maximize growth while reducing energy consumption. This is because indoor vertical farming allows for complete control of lighting, unlike typical production.
Understanding the plant’s internal rhythm may help optimize plant growth, control the best time for watering and indicate when fertilizers or other chemicals will have the most effect.
The last 25 years have seen a huge amount of research into the genetic control mechanisms of the circadian clock. The challenge now is to apply that knowledge to agriculture.
It’s in our interest to make sure we understand plants in this way, because we can use that knowledge to better farm our food and make our crops more resilient.
– Katharine Hubbard is a Reader in Biological Sciences Education, University of Hull, U.K. This article first appeared in the Conversation, by Reuters and was previously published at the Manitoba Co-operator.
