Melatonin-Mediated Molecular Responses in Plants: Enhancing Stress Tolerance and Mitigating Environmental Challenges in Cereal Crop Production

Abstract

Cereal crops are crucial for global food security; however, they are susceptible to various environmental stresses that significantly hamper their productivity. In response, melatonin has emerged as a promising regulator, offering potential benefits for stress tolerance and crop growth. This review explores the effects of melatonin on maize, sorghum, millet, rice, barley, and wheat, aiming to enhance their resilience to stress. The application of melatonin has shown promising outcomes, improving water use efficiency and reducing transpiration rates in millet under drought stress conditions. Furthermore, it enhances the salinity and heavy metal tolerance of millet by regulating the activity of stress-responsive genes. Similarly, melatonin application in sorghum enhances its resistance to high temperatures, low humidity, and nutrient deficiency, potentially involving the modulation of antioxidant defense and aspects related to photosynthetic genes. Melatonin also exerts protective effects against drought, salinity, heavy metal, extreme temperatures, and waterlogging stresses in maize, wheat, rice, and barley crops by decreasing reactive oxygen species (ROS) production through regulating the antioxidant defense system. The molecular reactions of melatonin upregulated photosynthesis, antioxidant defense mechanisms, the metabolic pathway, and genes and downregulated stress susceptibility genes. In conclusion, melatonin serves as a versatile tool in cereal crops, bolstering stress resistance and promoting sustainable development. Further investigations are warranted to elucidate the underlying molecular mechanisms and refine application techniques to fully harness the potential role of melatonin in cereal crop production systems.

Keywords: antioxidant defense; drought stress; heavy metal stress; melatonin; molecular regulation; sustainable agriculture.

Figure 1

Effect of melatonin application on oxidative stress, relative water content, photosynthesis, nutrient uptake, ion toxicity, enzymatic activities, stomatal traits, chloroplast structure, and enhanced tolerance in cereal crops under abiotic stress. Red arrows indicate downregulation, and green arrows indicate upregulation of physiological and biochemical processes.

Figure 2

Melatonin and Ca²⁺ affected phenolic acid biosynthesis and enhanced tolerance in barley under NaCl stress. The schematic model shows the effect of melatonin on heavy metal accumulation, toxicity, and salinity stress in cereal crops. Melatonin treatment increased the activity of antioxidative enzymes (SOD, POD, CAT, and APX) and decreased the content of MDA in leaves. Additionally, it regulated the expression of cadmium (Cd) transport genes, namely OsNramp1, OsNramp5, OsHMA2, OsHMA3), OsLCD, and OsPCR1, associated with Cd transport in response to heavy metal stress in both roots and shoots. Green arrows indicate downregulation, and red arrows indicate upregulation of the respective pathways and gene expressions. MDA: malondialdehyde; CAT: catalase; SOD: superoxide dismutase; POD: peroxidase; APX: ascorbate peroxidase; PAL: phenylalanine ammonia-lyase; 4CL: 4-coumarate-CoA ligase; ROS: reactive oxygen species.

Figure 3

The effects of melatonin on the maximum efficiency of PSII photochemistry (Fv/Fm); non-photochemical quenching coefficient (NPQ), photochemical quenching and ΦPSII (qP). and quantum yield of PSII electron transport (ΦPSII) in maize seedlings under salinity stress. Quantitative mean values ± SD (n = 3) are shown below the individual fluorescence images. The legend is as follows: control, 0 NaCl + 0 melatonin (CK), 150 mM NaCl + 0 melatonin (Na), 0 NaCl + 20 μM melatonin (M1), 0 NaCl + 100 μM melatonin (M2), 150 mM NaCl + 20 μM melatonin (M1 + Na), and 150 mM NaCl + 100 μM melatonin (M2 + Na). Reproduced with the permission of [68] © (2018) Wiley.

Figure 4

Foliar application of salicylic acid (SA) and melatonin (MT) reduces salinity stress in wheat by increasing root H⁺-pump activity, membrane stability index (MSI), polyphenol oxidase (PPO), ATP content, vacuole membrane H⁺-pump activity (VM H⁺), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and water content and mitigating production of reactive oxygen species (ROS), resulting in preserving ionic homeostasis. The upward arrow indicates upregulation, and the downward arrow indicates downregulation.