Caffeic acid, a natural phenolic compound, plays a multifaceted and positive role in helping plants cope with abiotic stresses such as low temperature, salinity, and drought. It primarily enhances plant resistance through core mechanisms such as strengthening antioxidant systems, protecting cell structure, and regulating osmotic substances.
Core Mechanism: Comprehensive Regulation from Genes to Phenotypes
The role of caffeic acid is not a single pathway, but rather spans multiple levels from the molecular and cellular levels to the entire plant.
1.Molecular Level: Regulation of Gene Expression
When plants encounter stresses such as drought and salinity, genes related to caffeic acid biosynthesis within cells are rapidly activated. Taking common bean (Phaseolus vulgaris) as an example, studies have found that drought stress significantly upregulates the expression of three key genes: phenylalanine ammonia-lyase (PAL), cinnamic acid-4-hydroxylase (C4H), and p-coumaric acid-3-hydroxylase (C3H). These genes act like “instructions” for caffeic acid production; their activity directly leads to the large-scale synthesis and accumulation of caffeic acid within cells. Under severe drought, in drought-resistant pinto bean leaves, the expression levels of these genes can even increase by more than 100%, thereby rapidly building a defense system.
2.At the cellular level: Strengthening the defense network
Efficiently removing “toxins”: Abiotic stress leads to the production of excessive reactive oxygen species (ROS) in plant cells, which act like “toxins” and damage cell structure. Caffeic acid itself is a potent antioxidant that can directly remove these harmful substances. More importantly, it significantly increases the activity of a series of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). These enzymes form a highly efficient “detoxification system,” converting ROS into harmless water and oxygen.
Protecting the cellular “skeleton”: The cell membrane and cell wall are the “skeleton” that maintains cell shape and function. Caffeic acid effectively protects the integrity of the cell membrane by reducing the accumulation of malondialdehyde (MDA, a product of membrane lipid peroxidation). Furthermore, caffeic acid is an important precursor for lignin synthesis, which strengthens the cell wall, providing more robust physical protection for the cell.
Regulating cellular “water”: Maintaining water is crucial in drought or high-salt environments. Caffeic acid promotes the accumulation of osmotic regulators such as proline and soluble sugars in plants. These substances act like “sponges,” helping cells retain water under low-moisture conditions and maintain normal turgor pressure and physiological functions.
3.At the plant level: Maintaining overall function.
Based on the aforementioned molecular and cellular mechanisms, caffeic acid ultimately exhibits positive effects on the overall plant. It protects photosynthetic machinery, maintaining high photosynthetic efficiency and chlorophyll content. Under stress, plants “enhanced” by caffeic acid show a smaller decline in biomass and yield, demonstrating stronger growth resilience and yield retention.
Differences in Performance Under Specific Stress Types
The role of caffeic acid varies slightly depending on the type of stress. The table below provides a clearer understanding:
| Stress Type | Specific Effects and Manifestations | Key Mechanisms/Indicator Changes | Research Subjects |
| Low Temperature Stress | Reduces chilling damage (e.g., leaf wilting), maintains normal plant growth | Enhances: Activity of antioxidant enzymes such as SOD, POD, CAT, and APX Increases: Proline and soluble sugar content Decreases: Reactive oxygen species (superoxide anion, H₂O₂) and MDA content | Cucumber Seedlings |
| Salt and Alkali Stress | Alleviates growth inhibition, increases biomass, and protects root nodule cell activity | Enhances: SOD (especially Mn-SOD and Cu/Zn-SOD isoenzymes) activity Decreases: Superoxide anion accumulation Increases: Photosynthetic pigment content and efficiency | Soybean, Lemon Balm |
| General Oxidative Damage (a common problem under various stresses) | Clears excess reactive oxygen species, protects cell membrane integrity, and delays tissue senescence | Activation: Ascorbate-glutathione (AsA-GSH) cycle enzyme system Upregulation: Expression of antioxidant enzyme genes (such as MdG6PDH6) and heat shock protein genes Regulation: Fatty acid metabolism, increasing unsaturated fatty acid content. | ‘Qiujin’ apple, and various other plants. |
Frontiers and Application Prospects
Currently, research on the application of caffeic acid is moving from the laboratory to the field, showing promising prospects.
Application Potential: As a natural biostimulant, caffeic acid holds promise for development into novel plant stress-resistance agents, helping crops withstand harsh environments through foliar spraying or irrigation. Particularly in legumes, research indicates it can effectively alleviate drought and salt damage, playing a crucial role in ensuring food security.
Technological Breakthrough: Nanocompositing: An exciting breakthrough is the application of caffeic acid nanocomposites. By preparing caffeic acid into nanoscale particles, its stability and absorption and utilization rate within plants can be greatly improved. A 2025 study showed that under salt stress, caffeic acid nanocomposites promoted lemon balm growth more effectively than free caffeic acid, demonstrating superior performance in multiple indicators, including photosynthesis and antioxidant enzyme activity. This provides a new approach to solving the application challenges of poor stability and easy degradation of natural products.
In summary, caffeic acid plays a central role in plants’ response to various abiotic stresses through a series of closely coordinated actions, including activating its own synthesis, strengthening the antioxidant network, protecting cell structure, and regulating osmotic balance.