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 (H2O2) and diphenyliodonium iodide (DPI) were applied to postharvest bamboo shoots to explore the regulation of H2O2 in the lignification process. Bamboo shoots, soaked in 10 mM H2O2 or 5 mM DPI for 10 min, were stored at 20 +/- 1 degrees C for 12 d. H2O2 treatment accelerated the accumulation of endogenous H2O2 by activating NADPH oxidase, while DPI treatment inhibited NADPH oxidase activity, leading to the decrease of endogenous H2O2. After 12 d of storage, the firmness and lignin content in H2O2-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 H2O2 activated the activities of PAL, C4H and 4CL, thus promoting lignin biosynthesis. Also, H2O2 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 H2O2-treated shoots. Our results indicated that endogenous H2O2 may play a vital role in the lignification process of bamboo shoots.