Changes in Lignin Content and Activity of Related Enzymes in the Endocarp During the Walnut Shell Development Period

Lignification was observed using the phloroglucinol–HCl method and the content of lignin, cellulose, and polyphenol and the activity of related enzymes were measured during development with the materials of walnut of ‘Zanmei’ and ‘Zhenzhuxiang’. Results showed that lignification occurred at the beginning of June, initially took shape in mid-June and finished in late July. From shell lignification to harvest, the concentrations of lignin, cellulose, and phenolic content increased before harvest, but phenolic content decreased slightly. The activities of both POD and PAL decreased and PPO varied somewhat. Correlation analysis showed lignin content to be significantly positively correlated with the cellulose content. Phenolic content had a significant positive correlation with that of lignin. Phenolic content was positively correlated with cellulose. The activity of POD had a significant negative correlation with lignin, cellulose, and phenolic content, but it was positively correlated with the activity of PAL.