Beneath the motionless surface that we perceive with the naked eye, plants lead an intense life, made up of continuous chemical exchanges, internal signals and rapid responses to the environment. Even when everything seems still, roots, stems and seeds communicate with each other to regulate growth and adapt to variations in light, water and soil quality. In this complex system, science has identified an unexpected protagonist: melatonin.
For humans, melatonin is mainly linked to sleep and circadian rhythms. In plants, however, the same molecule performs completely different functions, becoming a true survival tool. The most recent studies show that plant melatonin promotes development, regulates daily cycles and helps plants defend themselves from environmental stress, such as extreme temperatures, drought or nutrient-poor soils.
According to Abdul Latif Khan, a researcher at the University of Houston:
Melatonin has established itself as a central molecule in agriculture thanks to its ability to stimulate plant growth and mitigate abiotic stresses.
This is why scientific interest around this compound is constantly increasing.
How does melatonin work in plants?
In plants, melatonin production follows a well-defined biochemical pathway. Plant cells transform tryptophan first into serotonin and then into melatonin, thanks to the coordinated action of different enzymes. The levels of this substance increase especially in the initial stages of growth and during the development of the seeds, crucial moments for the survival of the species.
The peculiarity lies in the fact that plant melatonin is not produced in just one point, but in different areas of the cell, including chloroplasts, cytoplasm and endoplasmic reticulum. This flexibility allows plants to react effectively to adverse conditions such as intense heat, cold, water shortages or the presence of toxic substances in the soil.
As Imad Aijaz, lead author of the study, explains:
In plants, the internal clock regulates processes such as gene expression, metabolism and protein stability, synchronizing them with daily and seasonal cycles.
Melatonin thus becomes a sort of central regulator of plant biological time.
A particularly interesting aspect concerns the link between plants and melatonin produced by soil microorganisms. Some bacteria and yeasts that live around the roots are able to synthesize melatonin, especially when they are in stressful conditions, such as high salinity, low temperatures or the presence of heavy metals.
Microbial species such as Bacillus, Pseudomonas, Lactobacillus and various yeasts can accumulate large quantities of melatonin, releasing it into the medium. This extra supply is absorbed by plants and helps strengthen roots, intensify pigmentation and improve stress tolerance in many agricultural crops.
Khan points out that «melatonin-producing microorganisms enrich the soil, improving the availability, absorption and transport of melatonin within plants, with positive effects on growth and resistance».
Melatonin cycles in plants and influence on growth
Plants also follow a daily melatonin cycle. During the night the levels increase, while with sunlight they decrease. This pattern allows the plant to coordinate fundamental functions such as the opening and closing of leaf stomata, energy management and the initiation of flowering.
Melatonin signals travel through specific chemical pathways and dedicated receptors, including PMTR1. As the molecule moves through plant tissues, growth patterns change, affecting seed germination, photosynthesis and the production of new seeds. Research shows that these mechanisms vary greatly between different species, seasons and plant organs.
Melatonin does not work alone. In plants it interacts with various hormones, helping to maintain a delicate balance between growth and defense. A significant example is the relationship with cytokinin, a hormone that keeps leaves green, active and functional for photosynthesis. Under stressful conditions, such as excess light or drought, leaves tend to age more quickly. Melatonin strengthens the action of cytokinin, sending a stronger signal to “stay green and operational.”
Another case concerns jasmonic acid, involved in defense responses. In situations of salt stress, this hormone can become excessively activated, slowing growth. Melatonin moderates this response, preventing the plant from wasting energy on useless defenses and allowing it to continue developing.
New perspectives for agriculture
In addition to benefiting plants, the melatonin present in the soil also modifies the microbial composition, supporting beneficial bacteria such as Proteobacteria and Actinobacteria and reducing the presence of harmful fungi. The processes that make nitrogen and phosphorus available also improve, while mycorrhizae become more efficient in supporting the roots.
Researchers are now developing engineered microorganisms capable of producing melatonin on their own, releasing it only when the plant sends stress signals. Early results show stronger roots, increased nutrient uptake and improved survival in harsh conditions, such as extreme heat or high salinity.
The study, published in the journal iSciencepaves the way for more natural and sustainable agricultural strategies, based on the intelligent use of melatonin.
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