Understanding the changes of phenylpropanoid metabolism and lignin accumulation in wounded cassava root during postharvest storage

The postharvest deterioration of cassava (Manihot esculenta Crantz) root which was caused by the wounds has severely hampered the development of the cassava industry. In this study, the deterioration rate and weight loss, the transcription and enzyme activity of key genes in the phenylpropane metabolism, and the accumulation of lignin and suberin were examined during wound healing of cassava root. The results showed that the deterioration rate and weight loss of cassava-resistant variety SC9 were 4.1 and 1.8 times lower than those of the susceptible SC6 on the seventh day of storage. The activities of phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD) of SC9 were significantly higher on the seventh day than at 0 h. By contrast with SC6, SC9 deposited a large amount of lignin and suberin in the wound site. The structural characteristics of wound healing tissues were analyzed by microscopic observation, revealing that the healing reaction of cassava roots prevented the penetration of toluidine blue and pathogen infection. The expression changes of genes related to the phenylpropanoid metabolism pathway and the accumulation of lignin during wound self-healing provide new ideas for solving postharvest deterioration of cassava roots.