Mechanism of Exogenous Dopamine Regulating Shine Muscat Grape in Response to Low-Temperature Stress

To reveal the mechanism by which exogenous dopamine (Da) regulates Shine Muscat grape (<i>Vitis labrusca</i> L. × <i>Vitis vinifera</i> L.) in response to low-temperature stress, annual Shine Muscat grape plants were used as material. Different concentrations of Da (0.2-1.0 mmol L^-1) were set to investigate its synergistic regulatory effects on grape photosynthetic protection, osmotic adjustment, ion homeostasis, antioxidant defense, and cold-responsive gene expression and to identify the optimal concentration and core pathways through correlation analysis. The results showed that low-temperature stress significantly inhibited plant growth, reduced photosynthetic efficiency, disrupted ion balance, induced oxidative damage, and downregulated the expression of cold-responsive genes. Da exhibited a "low-concentration promotion and high-concentration inhibition" effect, with the 0.4 mmol L^-1 treatment showing the best performance: growth indicators such as plant height and stem diameter increased by 22.4-52.2% compared with the low-temperature stress group; photosynthetic parameters and photosystem II (PSII) function were significantly improved; proline content increased by 40.3%; the Na⁺/K⁺ ratio decreased by 44.8%; activity of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD) increased by 31.7-49.5%; and the expression of genes in the C-repeat binding factor (<i>CBF</i>) family was upregulated. Correlation analysis confirmed that the activity of SOD and catalase (CAT) showed a highly significant positive correlation with growth indicators (r > 0.8, <i>p</i> < 0.01) and a highly significant negative correlation with malondialdehyde (MDA) content (r < -0.8, <i>p</i> < 0.01), indicating that antioxidant defense is the core pathway. In conclusion, exogenous Da enhances the cold tolerance of Shine Muscat grape through multi-pathway synergy, with 0.4 mmol L^-1 the optimal concentration, which can provide a theoretical basis for cold-resistant cultivation of grapes.