Abstract: In order to explore the effect of exogenous 24-epibrassinolide (EBR) treatment on preventing chilling injury (CI) and the possible underlying mechanism in baby ginger rhizome, ‘Zhugen’ ginger rhizomes were treated with EBR for 30 min, sun-dried and then stored at 4 ℃ for up to 25 days. Changes in CI index, firmness, relative electric conductivity, the contents of hydrogen peroxide (H2O2), malondialdehyde (MDA) and total phenolics, and enzyme activities associated with reactive oxygen species (ROS) and phenolic metabolism were analyzed regularly during the storage period. Results showed that 10 μmol/L EBR treatment distinctly alleviated CI symptoms during cold storage. At the end of storage, CI index and total color difference (ΔE) in the EBR-treated group were 51.8% (P < 0.05) and 48.1% (P < 0.01) as compared to the control group, respectively, and firmness was 38.6% higher than that in the control group (P < 0.01). Relative electric conductivity, MDA content and H2O2 content in EBR-treated group were decreased by 24.6%, 10.5% and 24.8%, respectively (P < 0.05 or 0.01), compared to the control group. The enzyme activities involved in ROS metabolism including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were increased by 9.0%, 35.7% and 33.2% (P < 0.01), respectively, indicating that EBR can maintain cell membrane integrity and suppress the accumulation of ROS. Meanwhile, total phenolic content and phenylalanine ammonia lyase (PAL) activity were 38.5% and 24.8% higher in the EBR-treated group than in the control group, but polyphenol oxidase (PPO) activity was 17.3% lower than that in the control at the end of storage. Correlation analysis demonstrated that CI index was significantly positively correlated with ΔE, relative electric conductivity, MDA content, SOD, PAL and PPO activity (P < 0.01), but significantly negatively correlated with firmness, CAT and APX activity (P < 0.05 or 0.01). These results suggest that EBR could enhance chilling tolerance of baby ginger rhizome by regulating enzyme activities related to ROS and phenolic metabolism and ameliorating ROS-induced oxidative damage.

Key words: baby ginger rhizome; 24-epibrassionolide; chilling injury; reactive oxygen species; phenolics