Synergistic effect of small molecule oligopeptides and rhamnolipids on enhancing cold stress tolerance in tea plants: insights from physiological and transcriptome analyses.

BACKGROUND: As a globally important economic crop, the growth and quality of tea plants are susceptible to low-temperature stress, which hinders photosynthesis, damages cellular structures and disrupts metabolism, severely affecting yield and quality. Small molecular oligopeptides (SMO) regulate plant stress resistance, whereas surfactants enhance foliar fertilizer penetration. However, their individual roles in cold resistance have been studied to some extent, but the combined effects and mechanisms remain unclear, making the combined approach a novel exploration to potentially synergistically improve cold tolerance. RESULTS: This study found that SMO combined with rhamnolipid significantly enhanced the cold resistance of tea plants under low-temperature stress. Compared to chemical surfactants (Tween 20), the biological surfactant rhamnolipids showed superior synergistic effects. Physiologically, the combined treatment increased the activity of antioxidant enzymes (superoxide dismutase, peroxidase and catalase) with statistical significance (P < 0.05), reduced malondialdehyde content, maintained higher levels of soluble proteins and sugars, minimized chlorophyll reduction and improved chlorophyll fluorescence parameters, including F/F (maximum photochemical efficiency), φ (maximum quantum efficiency of photosystem II) and PI (performance index on absorption basis). Transcriptomic analysis revealed upregulated expression of genes related to photosynthesis (e.g. CsLHCB), flavonoid biosynthesis (e.g. CsCHS) and antioxidants (e.g. CsGPX and CsGST), which protect the photosynthetic system and clear reactive oxygen species. CONCLUSION: SMO combined with rhamnolipids enhance tea plants' cold stress adaptability by boosting antioxidant defense, maintaining photosynthetic function and regulating stress-related genes. This strategy provides an effective cold resistance solution for tea cultivation in cold regions and supports research on plant stress physiology and sustainable agriculture. © 2025 Society of Chemical Industry.