Hydrogen peroxide accelerated the lignification process of bamboo shoots by activating the phenylpropanoid pathway and programmed cell death in postharvest storage

Lignification is a typical characteristic of senescence of bamboo shoots during postharvest storage. In this study, exogenous hydrogen peroxide (H ₂ O ₂ ) and diphenyliodonium iodide (DPI) were applied to postharvest bamboo shoots to explore the regulation of H ₂ O ₂ in the lignification process. Bamboo shoots, soaked in 10 mM H ₂ O ₂ or 5 mM DPI for 10 min, were stored at 20 ± 1 °C for 12 d. H ₂ O ₂ treatment accelerated the accumulation of endogenous H ₂ O ₂ by activating NADPH oxidase, while DPI treatment inhibited NADPH oxidase activity, leading to the decrease of endogenous H ₂ O _2. After 12 d of storage, the firmness and lignin content in H ₂ O ₂ -treated shoots was 4.79% and 5.14% higher, respectively, than in the control shoots. However, DPI treatment showed the opposite effects, with 10.88% less firmness and 19.23% less lignin content observed as compared with the control group. High level of endogenous H ₂ O ₂ activated the activities of PAL, C4H and 4CL, thus promoting lignin biosynthesis. Also, H ₂ O ₂ upregulated DNase, RNase and caspase 3-like activities, leading to the acceleration of the programmed cell death process, which finally contributed to the resulting lignification. Transmission electron microscopy further revealed thickened cell walls and the decompartmentalization of cellular structure in H ₂ O ₂ -treated shoots. Our results indicated that endogenous H ₂ O ₂ may play a vital role in the lignification process of bamboo shoots.