Exploring signal transduction pathways from exogenous to endogenous salicylic acid in wheat and maize under stress conditions
Explore the SciencePlants are silent warriors, constantly battling against invisible enemies—drought, salt-infested soils, extreme temperatures, and pathogen attacks.
Unlike animals, plants cannot escape these threats by moving away. Instead, they've evolved sophisticated chemical signaling systems that activate their defense mechanisms. Among these protective compounds, salicylic acid (SA) has emerged as a powerful plant hormone that helps crops like wheat and maize withstand environmental stresses.
Originally known for its role in pain relief in humans (as the active component of aspirin), salicylic acid serves an entirely different purpose in plants—it's a master signal transducer that orchestrates complex defense responses against various threats 3 .
Salicylic acid enhances natural resilience, potentially reducing the need for chemical pesticides
Plants perceive external signals through sophisticated biochemical networks that convert environmental information into cellular responses. This process involves:
Salicylic acid is synthesized naturally in plants through two main biochemical pathways:
In wheat and maize, SA functions as a crucial signaling molecule that modulates various physiological processes, including:
When salicylic acid is applied to wheat or maize plants—whether through foliar spraying or seed priming—it must first penetrate plant tissues to initiate its protective effects. Research has shown that the method of application significantly influences SA's effectiveness 6 .
Once inside the plant cells, SA binds to specific receptor proteins (NPR proteins) that initiate the signaling cascade. The SA signaling pathway involves several key steps:
The ultimate outcome of SA signaling is the activation of various defense mechanisms:
SA signaling interacts with other hormone pathways, including jasmonic acid (JA), abscisic acid (ABA), and ethylene signaling. Research on barley under salt stress has revealed that exogenous SA application has antagonistic effects on levels of ABA, JA, ethylene, and most cytokinins, while having a synergistic effect on auxin (IAA) levels 2 .
A study investigated how maize primary roots respond to combined drought and heat stress 4 :
| Metabolite Category | Specific Metabolites | Change Under Stress | Proposed Function |
|---|---|---|---|
| Amino acids | Proline, Valine, Asparagine | Decreased | Osmoprotection, Nitrogen storage |
| Organic acids | Salicylic acid, Shikimic acid | Decreased | Defense signaling, SA biosynthesis |
| Sugars | Sucrose, Glucose | Increased (Sucrose), Decreased (Glucose) | Energy source, Osmoprotection |
| Fatty acids | Octadecanoic acid, Hexadecenoic acid | Decreased | Membrane integrity |
The decreased accumulation of SA and its precursors suggests rapid utilization during stress response. The transcriptional changes in phenylalanine metabolism genes indicate possible redirection of phenylalanine away from SA biosynthesis or increased SA turnover. The interaction between SA and other hormone pathways demonstrates that plants integrate signals from multiple stressors to mount appropriate defense responses 4 .
| Reagent/Tool | Function | Application Example |
|---|---|---|
| Salicylic acid solutions | Exogenous application to study SA effects | Foliar spraying or seed priming to enhance stress tolerance 6 |
| NPR protein mutants | Genetic manipulation of SA receptors | Studying SA perception and signal transduction mechanisms 3 |
| Antioxidant assay kits | Quantify oxidative stress levels | Measuring SA's effect on antioxidant defense systems 1 |
| Hormone quantification methods | Measure endogenous phytohormone levels | Analyzing SA's effect on other hormones like ABA, JA, IAA 2 |
| Transcriptomic technologies | Analyze gene expression changes | Identifying SA-regulated genes under stress conditions 4 |
| Metabolomic platforms | Profile metabolic changes | Detecting alterations in metabolic pathways under SA treatment 4 |
In barley, foliar application of SA (1 mg/L) improved growth parameters, photosynthetic pigments, and yield attributes under salinity stress (120 mM NaCl) .
In maize under lead and zinc stress, SA application (especially at 1500 μM) improved photosynthetic parameters, plant biomass, and anatomical features 6 .
In waxy maize, SA application prolonged the grain-filling period, promoted starch synthesis, and increased yield under heat stress 7 .
The study of salicylic acid-mediated signal transduction in wheat and maize reveals the remarkable complexity of plant defense systems.
From the initial perception of external stress to the activation of comprehensive defense mechanisms, SA serves as a central coordinator that helps plants survive under challenging conditions. The research shows that applying SA externally can enhance the plant's natural defense capabilities, potentially offering a sustainable approach to improving crop resilience.
As climate change increases the frequency and intensity of environmental stresses, understanding and harnessing natural defense mechanisms like SA signaling becomes increasingly important for agricultural sustainability. The intricate cross-talk between SA and other hormone pathways demonstrates that plants have evolved sophisticated systems to integrate information about multiple stressors and mount appropriate responses.
By learning from and enhancing nature's own defense systems, we may develop more sustainable approaches to crop production that can feed a growing global population in the face of environmental challenges.