Boosting tea plant survival: AMHA activates a powerful defense against chilling damage
image: A putative regulatory work model showing how AMHA is involved in mitigating cold damage in tea plant. AMHA pretreatment elicits physiological responses, including enhanced antioxidant enzymes, chloroplast protection, and osmotic adjustment, while also affecting the expression levels of glutathione S-transferase (GST). AMHA significantly increases the levels of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), anthocyanins, β-carotenes, ascorbic acid (AsA), glutathione (GSH), and soluble sugars, which are related to cold stress resistance. This alleviates physiological and metabolic damages, such as impaired photosynthetic efficiency, increased reactive oxygen species (ROS), and disrupted osmotic stability, caused by cold stress. AMHA mitigates the damage of cold stress by inducing the expression levels of CsGSTU7 and other key genes, as well as by stimulating the synthesis of the AsA-GSH system. AMHA maintains normal tea plant growth under cold-stress exposure by inducing genes related to cold resistance and osmolyte production.
Credit: Horticulture Research
A new study reveals that the natural plant resistance inducer 2-amino-3-methylhexanoic acid (AMHA) significantly enhances cold tolerance in tea plants by strengthening antioxidant capacity and stabilizing photosynthesis AMHA pretreatment effectively reduces leaf injury, suppresses excessive reactive oxygen species (ROS), and promotes osmotic adjustment under low temperatures. Transcriptomic analyses show that AMHA activates genes associated with the ascorbate–glutathione cycle, flavonoid and carotenoid biosynthesis, and particularly upregulates CsGSTU7, a key glutathione S-transferase involved in redox balance. Functional experiments confirm that CsGSTU7 is essential for mitigating oxidative stress and sustaining photosynthetic activity. Together, these findings highlight AMHA as a promising strategy to protect tea crops from cold damage.
Cold stress is one of the most damaging environmental factors limiting tea plant growth, disrupting photosynthesis, impairing membrane stability, and triggering toxic ROS accumulation that severely reduces yield and quality Traditional agronomic practices offer limited protection, prompting increasing interest in natural plant resistance inducers that enhance stress resilience through metabolic and transcriptional regulation. Previous studies have shown that melatonin, chitosan oligosaccharides, and amino acids improve cold tolerance by reinforcing antioxidant systems and stabilizing leaf physiology. However, the molecular mechanisms behind AMHA—a recently identified natural inducer with broad-spectrum protective effects—remain poorly understood. Due to these challenges, an in-depth investigation of AMHA-mediated cold-stress responses is urgently needed.
Researchers from the Tea Science Research Institute and Weed Research Laboratory at Nanjing Agricultural University, together with collaborators from Wilfrid Laurier University in Canada, published (DOI: 10.1093/hr/uhaf073) new findings in Horticulture Research on March 5, 2025. They reported that AMHA pretreatment enhances cold resistance in tea plants by improving photosynthetic performance, boosting antioxidant capacity, and activating key stress-responsive genes.
The researchers first evaluated the physiological response of AMHA-treated tea plants exposed to –4 °C. AMHA significantly reduced leaf wilting, preserved chlorophyll content, and maintained higher FV/FM and PIABS values, indicating better photosynthetic function under cold stress. Compared with untreated plants, AMHA-pretreated leaves exhibited lower accumulation of H₂O₂ and O₂⁻·, reduced lipid peroxidation, and higher levels of proline, soluble proteins, and sugars, demonstrating improved osmotic adjustment and redox stability. Enzymatic assays confirmed enhanced activities of SOD, CAT, POD, APX, and GST, while metabolite analyses revealed elevated levels of ascorbic acid, glutathione, flavonoids, anthocyanins, and β-carotene.
Transcriptome profiling across pretreatment, cold exposure, and recovery stages identified extensive AMHA-responsive genes enriched in pathways related to the AsA–GSH cycle, flavonoid biosynthesis, carotenoid biosynthesis, and photosynthetic electron transport. A key discovery was the consistent upregulation of CsGSTU7 and other glutathione S-transferases. Gene-silencing experiments showed that loss of CsGSTU7 increased ROS accumulation and cold hypersensitivity, whereas overexpression enhanced GST activity and antioxidant defenses. A regulatory network analysis further highlighted ERF-family transcription factors as potential upstream regulators coordinating AMHA-induced metabolic reprogramming.
According to the study’s authors, AMHA functions as a powerful bio-stimulant capable of priming tea plants against rapid cold-induced oxidative imbalance. They emphasize that CsGSTU7 plays a pivotal role by accelerating ROS detoxification and sustaining cellular redox homeostasis during stress conditions. The team notes that AMHA simultaneously enhances multiple protective pathways—photosynthetic stabilization, osmotic balance, and antioxidant metabolism—resulting in a coordinated defense response. These mechanistic insights, they argue, not only advance scientific understanding of cold-stress regulation but also highlight the practical potential of natural inducers in sustainable tea production.
The findings provide a strong foundation for applying AMHA as an eco-friendly, low-cost cold-resilience enhancer in tea cultivation. By boosting antioxidant capacity and activating genes essential for ROS detoxification, AMHA could help mitigate yield losses caused by frost events and expand suitable production regions. Its ability to promote flavonoid and carotenoid biosynthesis also suggests possible benefits for tea quality and nutritional value. Beyond tea, the mechanisms identified—particularly the central role of GST-mediated redox regulation—may inform the development of natural resistance inducers for other sensitive crops. This work opens new avenues for climate-adaptive agricultural technologies.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf073
Funding information
This work was supported by the National Key R&D Program of China (2023YFD17006000), Major science and technology projects in Yunnan Province (202402AE090015), National Natural Science Foundation of China (32160729), China Agriculture Research System of MOF and MARA (CARS-19), Hainan Nongken Investment Holding Group Co., Ltd (HKKJ202426), and Suzhou science and technology project (SNG2023001), and Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX24_0963).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.