Chemical Responsible for Ripening also dictates Plant’s Circadian Rhythm
There’s a ticking clock that your whole life is based on/around and it isn’t your alarm clock (could be a time bomb, given special situations). Most of us don’t notice our internal clocks until they’re out of whack with the time of day, usually because of jetlag or a change in sleep patterns.
Like a clock that needs to be set daily, the brain’s circadian clock requires a cycle of sunlight and darkness to orchestrate the body’s functions. “Circa” in circadian essentially means “around” and “Diem” means “day” in Latin.
Almost every function of the body oscillates during the day according to this clock, affecting the timing of major events- like birth or even death. Evolved over several millennia, circadian clocks are exquisitely entrained to natural light-dark cycles and allow our bodies to run “on optimal time”. During the bright-lit day, our internal clock tells us to increase energy intake and expenditure and cognition; after sundown, it promotes sleep by increasing the levels of melatonin.
Most plants have similar cycles. During the day, little solar farms in a plant’s leaves ‘wake up’ and convert sunlight and carbon dioxide to sugar through
photosynthesis, then at night, this system switches off. Many other plant processes follow a similar cycle, with some more active in the day, and some more active at night.Now, Ethylene is one of the keys to maintaining a plant’s circadian rhythm, researchers at the University of Melbourne have found.
While exploring the genes and proteins that regulate the circadian clock in Arabidopsis, a research collaboration led by Dr. Haydon and Professor Alex Webb at the Universities of Melbourne, Cambridge and York discovered that ethylene is one of the keys to maintaining the plant’s circadian rhythm.
Popularly regarded the “miracle chemical” that brings about ripening of fruits- most famous being the bananas, Ethylene also has important roles in plant growth and responses to pathogens or other stresses.
“Ethylene gas is a way for plants to communicate with each other, ensuring, for example, the fruit all ripen at the same time,” says Mike Haydon, from the School of BioSciences at the University of Melbourne.
In plants, research has shown that environmental cues like temperature and sunlight regulate circadian cycles. However, put a plant in a dark cupboard, and many of these day-night processes continue. But how?
This is what Dr. Haydon set out to find.
“We knew that ethylene production follows the day-night cycle, but we didn’t know that it also feeds back in to help regulate this cycle,” says Dr. Haydon.
“There is a well-defined network of receptor proteins and transcription factors that mediate ethylene signaling in plants. This ethylene signaling pathway promotes circadian rhythms by acting on the clock-regulating genes, GIGANTEA, which is also regulated by sugar.
“We found that ethylene reduced the circadian period, but this effect was blocked by sugar.”
Circadian clocks regulate the 24-hour cycles of plants, but Dr. Haydon says there are other ‘clocks’ that respond to longer time-scales, like seasonal cycles, and these long-term aging processes, which are heavily influenced by ethylene, could be impacted by disruptions to circadian clocks.
“By manipulating these we could fine-tune development rates to optimize crop yields or shelf-life,” he says.
