You know melatonin as the “sleep hormone” – the supplement you take to help you rest. But did you know that plants make melatonin too? And that this tiny molecule might be the secret to growing stronger, more resilient crops while reducing the need for chemical pesticides?
A comprehensive review published in the journal Advanced Agrochem has gathered the latest evidence on melatonin in plants – and the findings are remarkable. Melatonin acts as an “angel” for plants, regulating their growth, protecting them from drought, salt, heat, and even fighting off fungal diseases.
This is not science fiction. It is happening in laboratories and fields right now. And it could change the future of agriculture.
The Discovery: Plants Make Their Own Melatonin
For decades, scientists thought melatonin was unique to animals. Then, in 1995, researchers discovered it in plants. Since then, we have learned that melatonin is produced in plant chloroplasts and mitochondria – the energy centers of plant cells. It is synthesized from the same building block (tryptophan) as in animals, but plants have developed their own unique pathways.
Why does this matter? Because melatonin is not just a passive molecule. It is an active regulator of nearly every stage of plant life – from seed to fruit.
What Melatonin Does for Plants (The “Angel” Effects)
The review describes melatonin as having “pleiotropic effects” – a fancy way of saying it does many good things at once. Here are the highlights:
1. Boosts seed germination. Melatonin acts as an antioxidant, protecting seeds from oxidative damage as they sprout. In cotton, 20 micromolar (μM) melatonin increased seed vigor. In wheat, 200 μM melatonin improved germination under salt stress.
2. Promotes root growth. Melatonin helps plants develop stronger, deeper roots by interacting with auxin (a plant growth hormone). In tomatoes, 50 μM melatonin promoted adventitious root formation. In rice, just 1 μM improved root elongation.
3. Delays leaf aging (senescence). Melatonin maintains chlorophyll and chloroplast integrity, keeping leaves green and functional longer. In Chinese flowering cabbage, melatonin suppressed the genes that cause leaf yellowing.
4. Improves fruit production and quality. In tomatoes, melatonin regulated antioxidant pathways and increased fruit resistance to diseases. It also enhanced fruit size by improving carbohydrate metabolism.
Table 1: How Melatonin Boosts Plant Growth (Selected Examples)
| Plant | Effect | Optimal Dose (μM) | Mechanism |
|---|---|---|---|
| Cotton | Faster seed germination | 20 | Increases antioxidant enzyme activity |
| Tomato | More adventitious roots | 50 | Induces auxin (IAA) accumulation |
| Rice | Longer roots | 1 | Regulates melatonin biosynthesis genes |
| Apple | More roots | 1.29 | Increases IAA levels and root development genes |
| Maize | Taller plants, larger leaves | 100 | Regulates nitrogen metabolism |
| Tomato | Better fruit quality & disease resistance | 50 | Regulates ROS, SA, JA pathways |
The Stress Shield: Melatonin Protects Plants from Climate Extremes
This is where melatonin becomes truly exciting for farmers. As climate change brings more droughts, heatwaves, and soil salinity, crops need help surviving. Melatonin provides that help – through multiple mechanisms.
Drought protection: Melatonin improves water retention, activates antioxidant enzymes, and helps plants accumulate osmo-protective compounds (proline, sugars, proteins). In rice, 100 μM melatonin enhanced drought tolerance. In apple trees, it promoted nutrient absorption under dry conditions.
Salt tolerance: Melatonin helps plants maintain ionic balance by reducing sodium uptake and improving the sodium/potassium ratio. In tomatoes, 100 μM melatonin improved osmotic adjustment under salt stress. In cucumbers, just 1 μM regulated antioxidant systems.
Heat protection: Melatonin activates heat-responsive genes and heat shock factors, protecting cellular structures. In tomatoes, 100 μM melatonin controlled excessive hydrogen peroxide and superoxide production. In soybeans, it balanced redox homeostasis.
Cold protection: Melatonin regulates gene expression to help plants survive freezing. In cucumbers, 100 μM melatonin improved cold storage tolerance.
Heavy metal protection: Melatonin reduces metal uptake and promotes chelation (binding) of toxic metals, sequestering them away from sensitive plant tissues. In tomatoes, 100 μM melatonin improved antioxidant responses to cadmium.
Table 2: Melatonin Protects Plants from Environmental Stresses
| Stress | Plant | Effective Dose (μM) | Key Benefit |
|---|---|---|---|
| Drought | Rice | 100 | ROS scavenging |
| Drought | Apple | 100 | Promotes nutrient absorption |
| Salt | Tomato | 100 | Osmotic adjustment |
| Salt | Cucumber | 1 | Regulates antioxidant systems |
| Heat | Tomato | 100 | Controls H₂O₂ and O₂•⁻ |
| Cold | Cucumber | 100 | Gene expression regulation |
| Cadmium | Tomato | 100 | Antioxidant & redox balance |
| UV | Soybean | 25 | Activates UV-B signaling pathway |
Fighting Fungal Diseases: Melatonin as a Natural Fungicide
Perhaps the most exciting recent discovery is that melatonin directly fights plant pathogens – and it does so in a way that could lead to new, environmentally friendly fungicides.
How it works: Melatonin targets a specific protein kinase (Mps1) that fungi need to infect plants. By blocking this protein, melatonin stops the fungus in its tracks – without harming the plant.
Researchers have shown that melatonin inhibits:
- Botrytis cinerea (gray mold) on tomatoes
- Xanthomonas oryzae (rice bacterial blight)
- Phytophthora nicotianae and P. infestans (potato late blight)
- Fusarium graminearum (wheat head blight)
Even better: Scientists have used melatonin’s structure as a template to design new, even more powerful antifungal compounds. One derivative, called Mt-23, shows broad-spectrum antifungal activity and is environmentally friendly. Another, M-12, inhibits fungal growth at just 40 μM by disrupting lipid metabolism and glycogen transfer.
The Synergy Effect: Melatonin Works Well with Others
Melatonin does not work alone. It partners with other plant hormones and even with conventional fungicides to create a “synergistic effect” – where the combination is more effective than either alone.
With plant hormones: Melatonin interacts with auxin (root growth), gibberellins (stem elongation), abscisic acid (stress response), ethylene (ripening), and salicylic acid (defense). Together, they form a complex regulatory network that helps plants balance growth and survival.
With fungicides: Melatonin works synergistically with ethylicin against potato blight, allowing lower doses of the chemical fungicide. It also enhances isoprothiolane against rice blast. This means farmers could use less synthetic fungicide while getting better results – good for the environment and for human health.
With soil remediation agents: Melatonin combined with nano-zero-valent iron (nZVI) significantly reduced cadmium uptake in rice by improving soil chemistry and microbial communities.
Why This Matters for You (Even If You Are Not a Farmer)
For consumers: Melatonin-treated crops could mean less pesticide residue on your food, longer-lasting produce, and potentially higher nutrient content.
For farmers: Melatonin offers a low-cost, natural tool to reduce crop losses from drought, salt, heat, and fungal diseases. It can be applied as a seed treatment, a soil drench, or a foliar spray. And because it is already present in plants, it is biodegradable and safe.
For the environment: Reducing synthetic fungicides and improving stress tolerance means less chemical runoff, healthier soil microbiomes, and more resilient food systems in the face of climate change.
For gardeners: You can already buy melatonin as a supplement. Some home gardeners experiment with diluted melatonin sprays to help their plants cope with heat waves or transplant shock. (Always research appropriate concentrations for your specific plants.)
The Future: From Melatonin to Next-Generation Agrochemicals
The review outlines exciting future directions:
- AI-guided design: Researchers are using machine learning to design new melatonin derivatives with even stronger antifungal activity.
- Fluorescence imaging: New techniques will help scientists see exactly where melatonin works inside plant cells.
- Nano-formulations: Encapsulating melatonin in nanoparticles could provide controlled release, making it more effective and longer-lasting.
- Synergy screening: Scientists are testing melatonin with other natural compounds to find powerful new combinations for crop protection.
Limitations (Honest and Transparent)
This is a review article, not a single experimental study. It summarizes the work of many researchers. While the evidence is strong and consistent, most studies have been conducted in greenhouses or growth chambers, not in large-scale commercial fields. Optimal doses vary by plant species, stress type, and application method. Farmers should consult local agricultural extension services for specific recommendations.
Also, regulatory approval for melatonin as a pesticide or stress protectant varies by country. In some places, it is considered a natural product and is already allowed; in others, it may require registration.
The Bottom Line
Melatonin is not just for human sleep. It is a remarkable plant hormone that protects crops from drought, salt, heat, cold, heavy metals, and fungal diseases – all while promoting growth, root development, and fruit quality.
The review’s authors call it the “angel of plant growth regulation and protection.” That might sound poetic, but the science is real. Melatonin works through multiple pathways to make plants stronger, more resilient, and more productive.
As climate change makes farming harder, and as consumers demand fewer synthetic pesticides, melatonin-based solutions could become an essential tool in sustainable agriculture. The “angel” molecule is ready for its close-up.
Reference: here
Other Articles: