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How moonlight affects the health of coffee trees

A French Agricultural Research Centre for International Development (CIRAD) study has shown that despite its very low intensity, moonlight affects coffee trees on a molecular level, and disrupts their circadian clock.

CIRAD says it would therefore be in the interests of the horticultural and market garden sectors to control the effect on crops of this type of light. The results of the study have just been published in the journal BMC Plant Biology.

“Our analysis of the differentially regulated genes seems to show that coffee trees see moonlight as a form of stress,” says Jean-Christophe Breitler, a CIRAD geneticist based in Mexico.

“It disrupts not just the genes in the circadian clock, but also many others controlled by them, such as genes linked to photosynthesis, lipid biosynthesis, growth control, and response to oxidative and heat stress.”

Science has previously shown that both moonlight and the lunar cycle can affect the biological cycles of many living beings. Plants, for their part, are particularly sensitive to local gravimetric variations caused by the moon rotating around the earth, which affect their growth and development.

CIRAD says this explains why many farmers, gardeners, and foresters have planted and harvested according to the moon’s cycle. But up until now, the effect of light the moon reflects on plants has not been determined, despite plants being known to be highly photosensitive.

Plants are fixed photosynthetic organisms and need to turn over the space of a day, and through the seasons, which they do by means of photoreceptors connected to their circadian clock.

It was while studying the circadian cycle of coffee trees and the way it is disrupted by climate change that a CIRAD team led by Benoît Bertrand and Hervé Etienne noticed the atypical expression of some of the major genes in the circadian clock during the night.

The plants in the greenhouse had been sampled on the day of the spring solstice, during a full moon. This sparked the researchers’ curiosity, and they decided to study moonlight and attempt to reproduce it, in controlled conditions, since “moonlight” is in fact merely reflected sunlight.

“What we found was that plant photoreceptors saw these low-intensity wavelengths as strong environmental signals,” Breitler says.

“By analysing the transcriptome of coffee trees, in other words the range of genes expressed, every three hours for 24 hours, under new moon and full moon conditions, we showed that 3387 of the 25,574 known genes in the coffee transcriptome were differentially regulated.”

Placing plants in a phytotron during a full moon – depriving them of its light – proved that it was indeed the light that was responsible, and not the local gravimetric change.

CIRAD says the results showed that moonlight may stress coffee trees, although the over-expression of some genes suggests that the effect on growth is mainly positive. Work is continuing to fully understand the effect of this type of light on plants, notably on their growth, which could be particularly useful for horticulture and market gardening.

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