The story of dopamine in plants is older than many researchers realise. The molecule was first detected in plant tissue in the saguaro cactus, where scientists observed a spike in endogenous dopamine within five minutes of tissue wounding, hinting at a protective role. Earlier work in 1958 had already identified catecholamines and serotonin in bananas, and dopamine was subsequently confirmed in banana peel and pulp, plantains and avocados. Bananas remain one of the richest known plant sources of the compound, and its antioxidant power there is striking: dopamine outperforms glutathione, ascorbic acid, catechin gallate and common synthetic antioxidants in free-radical scavenging assays. What has changed in recent years is the depth of mechanistic understanding, with studies now tracing dopamine’s effects from gene expression to whole-plant physiology.

Chemically, dopamine is identical across kingdoms. It is a benzene ring bearing two adjacent hydroxyl groups, the catechol moiety characteristic of catecholamines, attached to an ethylamine side chain. That catechol group is the secret of its antioxidant behaviour, donating electrons and hydrogen atoms to neutralise reactive oxygen species and, in some cases, chelating metals to disarm free radicals. The primary amine makes dopamine an organic base capable of forming salts in acidic conditions, while both functional groups hydrogen-bond readily with water, making the molecule highly polar. In animals, dopamine is synthesised from the amino acid tyrosine through a single route in which tyrosine hydroxylase acts as the rate-limiting enzyme. Plants, remarkably, run two alternative pathways: one decarboxylates tyrosine to tyramine via tyrosine decarboxylase before hydroxylation by monophenol hydroxylase, while the other hydroxylates tyrosine to L-DOPA first and then decarboxylates it with DOPA decarboxylase. Which route dominates depends on enzyme availability and plant species.

Inside the plant cell, dopamine appears to accumulate mainly in the vacuole, which serves as a storage compartment, with smaller quantities detected in the cytoplasm. Its production sites shift with need, from roots to leaves, and its concentration ranges from nanograms to micrograms depending on species and developmental stage. In opium poppy, dopamine is synthesised in young rosette leaves and declines as flowering begins. This spatial and temporal flexibility underscores a key theme of the review: dopamine is not a static metabolite but a dynamic, stress-responsive signal whose behaviour is tailored to the tissue, the species and the threat at hand.

The physiological reach of dopamine in plants is broad. Under stress, photosynthesis typically collapses as reactive oxygen species oxidise the pigments that capture light, forcing plants to close their stomata and conserve energy at the cost of growth. Dopamine intervenes at multiple points in this cascade. It stabilises the light-dependent reactions of photosynthesis, maintains stomatal conductance, preserves chlorophyll and supports optimal transpiration and carbon assimilation. In apple seedlings exposed to drought, a treatment of 100 micromolar dopamine enhanced net photosynthetic rate, relative water content, stomatal conductance and the content of chlorophyll a and b. Dopamine also reshapes root architecture, stimulating root vigour and elongation so that plants can explore soil for water and nutrients more effectively. Intriguingly, roots themselves secrete dopamine as a major exo-metabolite, suggesting it plays an active role at the root-soil-microbe interface.

At the molecular level, dopamine’s influence extends deep into gene regulation. Transcriptomic analysis of drought-stressed apple plants treated with dopamine revealed upregulation of calmodulin and calmodulin-like genes and cyclic nucleotide-gated channels involved in calcium signalling. The transient elevation of cytosolic calcium during stress initiates a cascade of adaptive cellular responses that activate downstream transcription factors, including MYBs and WRKYs. Because superoxide dismutase is a calmodulin-dependent enzyme, and glutathione peroxidase activation is also linked to calmodulin, dopamine’s calcium signalling effectively amplifies the plant’s antioxidant arsenal. The review also documents dopamine’s extensive crosstalk with phytohormones, including auxin, gibberellic acid, melatonin, abscisic acid, jasmonic acid and ethylene, fine-tuning the growth-defence trade-offs that determine how a plant allocates its limited resources under threat.

Each stress type reveals a different facet of dopamine’s versatility. Under salinity, exogenous dopamine in Malus hupehensis inhibited excess sodium and chloride uptake while enhancing the acquisition of potassium, nitrogen, phosphorus, sulphur, copper and manganese. Upregulation of genes such as MdHKT1, MdNHX1 and MdSOS1 shows dopamine engaging the salt overly sensitive pathway, the core salt-defence system in plants, pumping sodium into vacuoles and expelling it from root cells. In tomato seedlings, 100 micromolar dopamine maintained calcium-to-sodium and potassium-to-sodium ratios and produced striking gains: root dry weight increased by 286.84 percent, plant height by 108.37 percent and leaf area by 158.28 percent compared with untreated controls. Under cadmium stress in apple, dopamine reshaped the rhizosphere microbial community, enriching beneficial bacteria such as Frankia, Bradyrhizobium and Streptomyces and shifting keystone species in ways that helped the plant resist the metal.

Nitrogen stress and temperature extremes add further chapters. In cucumber grown under excess nitrate, 150 micromolar dopamine improved root growth, photosynthesis and antioxidant activity while upregulating genes for sucrose phosphate synthase, nitrate reductase and other enzymes that coordinate carbon and nitrogen metabolism. In apple, dopamine under low-nitrogen conditions increased expression of nitrate transporter genes and activated MdORG2, a transcription factor that boosts the plant’s own dopamine-synthesising machinery. Against cold, dopamine protected watermelon and grape seedlings by accumulating polyamines and osmolytes and bolstering antioxidant systems. Perhaps most commercially intriguing are the postharvest results: dopamine treatment significantly mitigated chilling injury in bananas stored at 7 degrees Celsius for 21 days and kiwifruits stored at 1 degree Celsius for 120 days, by activating the phenylpropanoid pathway, raising endogenous proline, GABA and glycine betaine, and preserving membrane integrity.

Dopamine also strengthens plant immunity against pathogens. In apple replant disease caused by Fusarium solani, 150 micromolar dopamine enhanced endogenous dopamine biosynthesis, reduced root damage and upregulated defence genes encoding chitinase and beta-1,3-glucanase, while increasing tyramine content and cell wall-bound amine deposition. Against Valsa mali infection in apple, resistance came through elevated phenolic content and salicylic acid. In pear, a foliar spray of 100 micromolar dopamine imparted resistance to Botryosphaeria dothidea by enhancing autophagy activity in host cells. Even allelopathic threats fall within its scope: dopamine counteracted phloridzin, a growth-inhibiting compound that disrupts apple rhizosphere communities, by lowering reactive oxygen species and enriching beneficial nitrogen-cycling microbes.

Significant gaps remain before dopamine can be deployed at scale. Research has concentrated on a narrow set of crops, chiefly apple rootstocks, tomato, cucumber and duckweed, while cereals, legumes and tropical fruits remain largely unexplored. Unlike in animals, no dopamine receptors have been identified or characterised in plants, leaving open the fundamental question of how the molecule is perceived. The threshold between beneficial and phytotoxic doses is poorly defined, and there is no regulatory framework governing exogenous dopamine use in agriculture. The review’s authors point to biotechnology as one promising route: overexpressing the tyrosine decarboxylase gene could raise endogenous dopamine levels and confer climate resilience without repeated spraying. Combined applications with melatonin, brassinosteroids and beneficial microbes offer further synergistic potential. If those mechanistic and safety questions can be answered, dopamine may graduate from laboratory curiosity to a next-generation regulator of crop resilience, extending its celebrated career from the animal brain to the world’s fields and orchards.

Subject of Research: The role of dopamine as a stress-regulating signalling molecule in plants

Article Title: Beyond neurotransmission: dopamine as an emerging biotic and abiotic stress regulator in plants

Article References: Shinde, D., & Pareek, S. (2026). Beyond neurotransmission: dopamine as an emerging biotic and abiotic stress regulator in plants. Stress Biology, 6(1), Article 24. https://doi.org/10.1007/s44154-026-00291-8

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00291-8

Keywords: dopamine, plant stress, abiotic stress, biotic stress, antioxidant, reactive oxygen species, calcium signalling, phytohormones, salinity tolerance, drought tolerance, postharvest, plant signalling

The first line of defence is mounted by pattern recognition receptors, or PRRs, which sit at the cell surface and detect conserved microbial molecules known as microbe-associated molecular patterns. These include bacterial flagellin, the translation factor EF-Tu, fungal chitin and bacterial peptidoglycan. When a PRR such as the flagellin receptor FLS2 binds its ligand, it recruits a co-receptor kinase called BAK1, forming an active receptor complex that triggers a cascade of phosphorylation events. Structural studies over the past decade have revealed the atomic details of these interactions, showing how ligand binding induces dimerization and allosteric activation of the kinase domains. The review emphasizes that receptor-like proteins, which lack an intracellular kinase domain, rely on partner kinases such as SOBIR1 and BAK1 to transduce signals, and that recent work has clarified how these complexes assemble and activate downstream pathways.

Once a PRR is activated, a receptor-like cytoplasmic kinase called BIK1 is released from the receptor complex and phosphorylates a remarkable range of targets. BIK1 directly activates the NADPH oxidase RbohD, driving a burst of reactive oxygen species that reinforces cell walls and signals to neighbouring cells. It also regulates calcium channels, including CNGCs and OSCA1.3, allowing cytosolic calcium concentrations to rise rapidly. This calcium influx is not merely a byproduct; it is a central hub of immune signalling. Calcium-dependent protein kinases decode the calcium signature and phosphorylate transcription factors and metabolic enzymes, while calcium-activated metacaspases release immunomodulatory peptides from damaged cells. The review highlights how this spatiotemporally controlled calcium symphony, as one group of researchers has described it, links pattern recognition to gene expression, stomatal closure and the production of antimicrobial compounds.

The second branch of plant immunity operates inside the cell. Intracellular nucleotide-binding leucine-rich repeat receptors, or NLRs, detect pathogen effectors, the virulence proteins that pathogens inject into host cells to suppress pattern-triggered immunity. The gene-for-gene concept, articulated by Harold Flor in the 1970s, predicted that for every resistance gene in the plant there is a corresponding avirulence gene in the pathogen. Decades of work have vindicated this idea at the molecular level. Some NLRs directly bind effectors, while others act as guards or decoys, monitoring host proteins that effectors modify. Integrated domains, which are fusions of host target mimics into the NLR architecture, allow single receptors to sense effectors that manipulate specific host processes. The review traces this conceptual evolution from the cloning of the first NLR genes in the 1990s to the recent explosion of structural biology that has revealed how these receptors work.

The most striking recent discovery in this field concerns resistosomes. When certain NLRs recognize their cognate effectors, they do not simply change shape; they oligomerize into large, ordered complexes that function as channels or enzymes. The ZAR1 resistosome, for example, forms a pentameric calcium-permeable channel in the plasma membrane, flooding the cytosol with calcium and triggering cell death at the infection site. Helper NLRs of the NRC and ADR1 families form hexameric resistosomes with similar channel activity, while TIR-domain-containing NLRs act as NAD-cleaving enzymes that produce small signalling molecules. Recent work has shown that helper NLR resistosome clusters assemble upon activation of sensor NLRs, and that a wheat CCG10-NLR receptor forms an octameric resistosome. These structures represent a remarkable convergence with animal immunity, where inflammasomes perform analogous functions, and they explain how a single molecular recognition event can be amplified into a full-scale defensive response.

Perhaps the most important conceptual shift in recent years is the recognition that pattern-triggered immunity and effector-triggered immunity are not separate pathways but mutually reinforcing branches of a single system. Studies published in 2021 demonstrated that PRR signalling is required for full NLR-mediated resistance, and that activation of TIR signalling boosts pattern-triggered responses. The EDS1-PAD4-ADR1 node, a complex of lipase-like proteins and helper NLRs, mediates both branches, providing a molecular bridge between cell surface and intracellular perception. This mutual potentiation means that a plant that has already mounted a pattern-triggered response is primed to respond more vigorously to effector recognition, and vice versa. The review argues that this integration explains why plants with compromised PRR function are often more susceptible to disease even when they possess functional NLR genes.

But immunity is expensive. Uncontrolled activation of PRRs or NLRs causes stunted growth, autoimmunity and reduced seed yield, a phenomenon known as the growth-defence trade-off. Plants have evolved multiple mechanisms to keep immune signalling in check. Negative regulators such as the protein phosphatase PP2C38 dephosphorylate BIK1, while ubiquitin ligases control BIK1 protein homeostasis. The BAK1 co-receptor is shared between immune receptors and the brassinosteroid growth receptor BRI1, creating a molecular competition between defence and growth signalling. BIK1 inversely modulates these two pathways, promoting immunity while suppressing brassinosteroid responses. Membrane nanodomains physically separate immune and growth receptor complexes, even when they share signalling components. The review also describes how phytosulfokine signalling, mediated by the receptor PSKR1, balances growth and defence in the rhizosphere, and how transcription factors such as BZR1 mediate trade-offs at the gene expression level.

Environmental conditions add another layer of complexity. Temperature, light and humidity all modulate immune responses. Elevated temperatures can suppress NLR-mediated resistance, but recent work has identified CBP60g family transcription factors as key determinants of temperature sensitivity, offering a route to climate-resilient immunity. Light quality matters too: the blue-light receptor CRY1 acts as a switch that balances photosynthesis and defence, while phytochromes regulate salicylic acid and jasmonic acid pathways in rice. High humidity dampens salicylic acid signalling and NPR1 function, promoting disease, and daily humidity oscillations entrain the circadian clock to influence plant physiology. The microbiome also plays a role, with rhizosphere bacteria suppressing local root immune responses through pH modulation, and leaf microbiota influencing autoimmunity in Arabidopsis. The review presents a schematic model of these interplays, emphasizing that immunity cannot be understood in isolation from the environment.

The practical implications are profound. Understanding the mechanisms of immune receptor activation and regulation opens the door to engineering disease-resistant crops with optimized fitness. Researchers have transferred PRRs between plant families to confer broad-spectrum bacterial resistance, stacked multiple PRRs in potato against Phytophthora infestans, and used reverse engineering of FLS2 to expand recognition of evasive flagellin epitopes. NLR engineering has progressed from single amino acid mutations that expand effector recognition to designer receptors with novel specificities, nanobody fusions that redirect NLRs to new targets, and interfamily co-transfer of sensor and helper NLR pairs. Genome editing of susceptibility genes has produced multipathogen resistance without agronomic penalty, and inducible overexpression of transcription factors such as Ideal Plant Architecture1 improves both yield and disease resistance in rice. Machine learning and AlphaFold-guided design are now being applied to predict effector targets and redesign immune proteins. The review concludes that the next frontier lies in combining these engineering strategies with a deep understanding of growth-defence balance, so that crops can be made both resistant and productive in a changing climate.

Subject of Research: Mechanisms of pathogen perception, immune signalling and growth-defence balance in plant immunity

Article Title: Mechanisms and balanced regulation of plant immunity

Article References: Chai, J., Wang, Y., & Wang, Y. (2026). Mechanisms and balanced regulation of plant immunity. Nature Reviews Molecular Cell Biology. https://doi.org/10.1038/s41580-026-01009-4

Image Credits: AI Generated

DOI: 10.1038/s41580-026-01009-4

Keywords: plant immunity, pattern recognition receptors, NLR receptors, resistosomes, calcium signalling, growth-defence trade-off, effector recognition, immune receptor engineering, BIK1, BAK1, PTI, ETI