Long-term improper use of chemical fertilizers has led to environmental degradation, soil fertility decline, and increased non-point source pollution, severely impacting ecosystems. The advent of bio-stimulants offers a promising solution to these issues. These substances, even in small quantities, can stimulate plants or environmental microorganisms, enhancing nutrient availability, improving nutrient uptake and utilization efficiency, and bolstering plant tolerance to abiotic stresses, thereby increasing crop yields. γ-Polyglutamic acid (γ-PGA), an anionic polymer composed of D- and L-glutamic acid units, possesses unique chemical properties, including strong water retention, fertilizer retention, and complexing capabilities, making it widely applicable in various fields, such as chemical engineering, food, and environmental science. Numerous studies have reported that γ-PGA application can increase crop yields, improve product quality, and enhance resistance to abiotic stresses, like drought, cold, and salinity.
Maize, a globally crucial food crop, is vital for food security, livestock feed, and industrial raw materials. However, in maize-growing regions across the globe, water scarcity poses a prevalent and acute challenge. During crucial growth phases of maize, particularly the large bell-mouth stage, inadequate water supply often arises, severely impeding the normal growth of the crop and substantially affecting global maize production.
Previous studies have shown that γ-PGA can improve drought resistance in crops like wheat and maize by regulating physiological processes, such as abscisic acid (ABA) synthesis, and enhancing photosynthetic efficiency. The method of soil application requires high dosage, resulting in increased costs. In contrast, studies on foliar application of γ-PGA as a bio-stimulant to enhance drought resistance have shown.
PGA Enhances Maize Growth and Yield
The results demonstrate that foliar application of γ-PGA significantly enhances the growth and yield of summer maize under both irrigated and non-irrigated conditions. The positive effects of γ-PGA on maize growth and yield can be attributed to its role in regulating key metabolic processes, including brassinosteroid biosynthesis, alpha-linolenic acid metabolism, phenylpropanoid biosynthesis, and nitrogen metabolism. RNA-seq data suggest that γ-PGA enhances photosynthesis by upregulating the expression of photosynthesis-related genes. Research on tobacco shows that it can regulate carbon-nitrogen metabolism in leaves, and in Chinese cabbage it enhances nitrogen metabolism related enzymes and nutrient contents in leaves. γ-PGA pretreatment activates Ca2+ signaling in plants, leading to H2O2 production and increased biosynthesis of stress hormones, like brassinolide and jasmonic acid. This promotes proline accumulation and enhances antioxidant capacity, improving stress tolerance and growth.
Research indicates that the application of γ-PGA significantly influences signal transduction in plants, thereby exerting a cascading regulatory effect on plant metabolic pathways. This regulation enhances plant growth and development, nutrient absorption, and pathways related to stress resistance. Under drought conditions, γ-PGA has been shown to upregulate genes related to ABA biosynthesis and signal transduction, increasing ABA content in maize and enhancing drought resistance. This is particularly relevant given that drought stress can cause a 53–64% reduction in maize yield, making it a critical factor in global maize production. By improving photosynthetic efficiency, root development, and nutrient uptake, γ-PGA helps mitigate the negative effects of water scarcity on maize growth and yield.
PGA Modulates Rhizosphere Microbiota
Foliar application of γ-PGA likely influences rhizosphere microbial communities indirectly through altered root exudation profiles. Previous studies showed that γ-PGA enhances root biomass and nutrient uptake, which increased the quantity and quality of maize root exudates (e.g., lipids, organic compounds, organic acids and derivatives) under drought stress. These exudates serve as microbial substrates, shaping community composition by favoring taxa with specific metabolic capabilities. For example, γ-PGA-treated maize in study exhibited enrichment of nitrogen-fixing Arthrobacter and phosphate-solubilizing Sphingomonas, which may be attributed to increased root exudation of organic acids that solubilize nutrients. Additionally, γ-PGA-induced drought tolerance could reduce stress-related exudates (e.g., phenolic compounds), creating a more favorable rhizosphere environment for beneficial microbes. In addition to root exudation-mediated effects, a portion of the foliar-applied γ-PGA may directly reach the soil through spray droplets, altering soil physicochemical properties and microbial communities. These microbial changes contribute to improved soil fertility, nutrient cycling, and plant stress tolerance, ultimately enhancing maize growth and yield.
Conclusions
There is a significant interactive effect between irrigation conditions and foliar application of γ-PGA on maize growth. The application of γ-PGA significantly increased maize yields by 33.3% to 37.0%. This indicated that in corn production areas with limited water supply or insufficient irrigation infrastructure, foliar spraying of γ-PGA can improve crop water use efficiency and effectively alleviate the inhibitory effect of drought stress on grain formation. These results highlighted the potential of γ-PGA as a bio-stimulant in agricultural applications, and also demonstrate its positive role in crop response to environmental stresses.
If you are concerned about γ-PGA or have other insights, you can contact us Dora team^^