Transcriptomic Insights into the Effect of Ultrasonic Treatment in Mung Bean Germination

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In a groundbreaking 2025 study published in LWT – Food Science and Technology, researchers from the Liaoning Academy of Agricultural Sciences and Shenyang Agricultural University revealed how ultrasound technology can transform the way we grow mung bean sprouts.

Mung bean sprouts are a global dietary staple, celebrated for their high levels of antioxidants, proteins, and vitamins. Antioxidants, such as flavonoids and polyphenols, are compounds that protect cells from damage caused by free radicals, reducing the risk of chronic diseases.

However, traditional germination methods are slow and often produce uneven results. In their quest to improve this process,

• scientists turned to ultrasound—a technology that uses high-frequency sound waves (above 20,000 Hz, beyond human hearing) to stimulate biological systems without heat or chemicals.

By analyzing four mung bean varieties and employing advanced molecular techniques like transcriptomics (the study of all RNA molecules in a cell), the researchers uncovered how sound waves interact with seeds at a cellular level, offering a blueprint for future agricultural innovations.

From Seed to Super Food: The Nutritional Journey of Mung Bean Sprouts

Mung beans (Vigna radiata L.) are nutrient-dense legumes, but their true potential emerges during germination—the process by which a seed develops into a new plant.

When seeds sprout, they activate enzymes that break down anti-nutrients like phytic acid (a compound that binds minerals, reducing their absorption) while synthesizing beneficial compounds such as flavonoids, polyphenols, and vitamin C. Flavonoids are plant pigments with anti-inflammatory properties, while polyphenols act as antioxidants.

For instance, dry mung beans contain no vitamin C, but after five days of germination, sprouts can accumulate up to 0.009 mg/g of this vital nutrient, which supports immune function and skin health. Despite these benefits, conventional sprouting methods face challenges.

Factors like temperature fluctuations and microbial contamination often lead to poor yields, while prolonged germination reduces carbohydrates and fats, compromising texture and taste.

Ultrasound technology, which uses high-frequency sound waves (20–100 kHz), has shown promise in agriculture. These waves create microscopic bubbles in liquids through a process called cavitation, generating mechanical forces that soften seed coats, enhance water absorption, and activate enzymes like α-amylase (which breaks down starches into sugars).

Prior studies found that ultrasound increases α-amylase activity in soybeans, accelerating sugar production. However, its effects on mung beans—and the genetic mechanisms behind them—remained unclear. This study bridges that gap by examining how ultrasound influences germination efficiency, nutrient profiles, and gene expression in mung beans.

The Experiment: Bridging Physics and Biology

The research team began by testing four mung bean varieties—PB05, PB08, PB10, and 10L717—under controlled conditions. Seeds were disinfected with sodium hypochlorite (a common disinfectant), soaked, and exposed to ultrasound at different frequencies (45–100 kHz), power levels (150–210 W), and durations (10–20 minutes).

Sprouts were harvested daily for up to seven days, with their growth metrics (length, weight) and nutrient levels meticulously tracked.

To measure nutrients, the team used advanced techniques. Spectrophotometry—a method that measures light absorption by chemicals—was used to quantify flavonoids and polyphenols.  For example,

• flavonoid content was determined by mixing extracts with sodium nitrate and aluminum nitrate, then measuring absorbance at 510 nm.
• Soluble proteins were analyzed via the Bradford assay, a colorimetric method that uses a dye to bind proteins, changing color intensity based on concentration.
• Vitamin C levels were assessed using the Kampfenkel method, which involves extracting the vitamin with metaphosphoric acid and measuring its reaction with a dye.
• Soluble sugars were measured with anthrone-sulfuric acid assays, where sugars react with anthrone to produce a blue-green color, proportional to sugar concentration.

Beyond nutrient analysis, the study employed transcriptomics to profile gene activity. RNA sequencing generated 39.74 GB of data, identifying 27,692 genes (25,866 known, 1,826 novel) in ultrasonicated vs. control sprouts.

Differential gene expression analysis (comparing gene activity between groups) revealed 964 genes with significant changes. Molecular assays, including Dual Luciferase Reporter (DLR) and Yeast One-Hybrid (Y1H) tests, confirmed how specific genes and proteins interact during ultrasound treatment.

DLR assays measure how proteins regulate gene promoters by linking them to luciferase enzymes (which produce light), while Y1H assays test DNA-protein binding in yeast cells.

Groundbreaking Results: Speed, Nutrients, and Genetic Insights

Among the four varieties tested, PB10 consistently outperformed the others.

By day five, PB10 sprouts were 15% longer than PB05 sprouts and contained 12.5 mg/g of flavonoids—a 15% increase over PB08.

Polyphenol levels in PB10 peaked at 9.2 mg/g, while soluble proteins reached 4.8 mg/g before declining.  Soluble proteins are crucial for plant growth, as they include enzymes and structural molecules. Vitamin C levels across all varieties peaked at day six (0.009 mg/g), but ultrasound-treated sprouts achieved these levels earlier, by day five.

The team identified optimal ultrasound parameters through response surface analysis—a statistical method that models how variables (e.g., power, frequency) affect outcomes. At 80 kHz frequency, 180 W power, and 15-minute duration, sprout weight surged to 0.323 g—compared to 0.28 g in untreated controls.

Exceeding these settings (e.g., >210 W or >20 minutes) damaged cells through excessive cavitation, while lower frequencies (<45 kHz) failed to penetrate seed coats effectively.

Transcriptomics revealed that ultrasound alters key phytohormone (plant hormone) pathways. Genes linked to jasmonic acid (JA)—a hormone that inhibits germination and promotes stress responses—were suppressed.

For example, the JA precursor 12-oxophytodienoic acid (OPDA) decreased by 1.7-fold, while JA synthesis genes (VrAOC3, VrAOC6) were downregulated. Allene oxide cyclase (AOC) enzymes, encoded by these genes, are critical for converting fatty acids into JA.

Conversely, genes associated with abscisic acid (ABA)—a hormone that regulates stress tolerance and seed dormancy—were activated. The transcription factor VrbZIP34 emerged as a critical player, binding to promoters of VrAOC3 and VrAOC6 to suppress JA production.

Transcription factors are proteins that control gene expression by attaching to specific DNA regions.

DLR assays showed that co-expressing VrbZIP34 with these genes in tobacco increased luminescence by 300%, confirming their interaction.

Y1H assays further validated that VrbZIP34 directly regulates JA pathways.

Why This Matters for Food Security and Health

The implications of this research are far-reaching. For consumers, ultrasound-treated sprouts offer higher antioxidants and vitamins in less time, supporting healthier diets. For example, flavonoids like quercetin and kaempferol in sprouts have been linked to reduced inflammation and heart disease risk.

Farmers benefit from faster germination and reduced water usage, as ultrasound-treated seeds absorb moisture more efficiently. This aligns with global sustainability goals by minimizing resource waste and replacing synthetic growth enhancers like gibberellins (plant hormones used to accelerate germination).

From a scientific perspective, the discovery of VrbZIP34 opens doors for genetic engineering. By editing this gene using tools like CRISPR-Cas9, researchers could enhance ultrasound responsiveness in other crops, such as soybeans or lentils.

Additionally, detecting JA precursors could help farmers optimize harvest times, maximizing nutrient retention. For instance, suppressing JA pathways might allow crops to grow faster under stress conditions like drought.

Challenges and Limitations

Despite its promise, the study has limitations. The PB10 variety responded exceptionally well to ultrasound, but PB05 showed minimal improvement, suggesting genetic variability—differences in DNA that affect trait expression.

High-frequency ultrasound equipment may also be costly for small-scale farmers, though bulk purchasing or subsidies could mitigate this.

Furthermore, while ultrasound disinfects seeds by disrupting microbial cell walls, excessive exposure might stress sprouts, requiring careful calibration to avoid oxidative damage (harm caused by free radicals).

The Future of Ultrasound in Agriculture

The researchers outline several next steps. Large-scale field trials will test ultrasound in diverse climates, as factors like humidity and soil type could affect results. Multi-omics studies (e.g., proteomics, metabolomics) could provide a holistic view of ultrasound’s effects by analyzing proteins and metabolites alongside genes.

Partnerships with vertical farms or packaged sprout producers may accelerate commercialization. For households, affordable, portable ultrasound devices could revolutionize home gardening, enabling anyone to grow nutrient-rich sprouts year-round.

Conclusion

This study revolutionizes agriculture by demonstrating how ultrasound technology accelerates mung bean sprout growth while enhancing nutritional value. By suppressing jasmonic acid (JA)—a “stress hormone” that slows germination—through the transcription factor VrbZIP34, ultrasound redirects the plant’s energy toward rapid, nutrient-rich growth.

As lead researcher Yinghao Xu states, ultrasound bridges traditional farming with modern biology, offering a sustainable path to food security and healthier diets. This breakthrough highlights the potential of sound waves to transform crop cultivation, benefiting consumers, farmers, and ecosystems alike.