Effects of Different Treatments on Postharvest Callus Formation and Metabolic Mechanisms in Taro

In this study, taro samples were artificially wounded and then underwent hot water treatment (HWT) at 65 ℃ or hot air treatment (HAT) at 30 ℃, whereas those naturally wounded served as a control. After storage for 0,2,4,6 and 14 days, wound appearance, suberin layer thickness and lignin staining were evaluated. Changes in reactive oxygen species (ROS) levels, metabolic enzyme activities, lignin accumulation and lignin synthesis-related enzyme activities were determined during callus formation in taro corms. The results showed that the thickness of the suberin layer as well as the accumulation of total phenols, flavonoids and lignin increased continuously during callus formation, and the levels of total phenols, flavonoids and lignin in the HAT group were higher than those in the HWT and control groups. In the HWT group, a dense suberin layer was observed to form during 2–4 days of storage, significantly earlier than the other two groups. Superoxide anion radical and H2O2 accumulated rapidly in the HAT group after 2 days, and the activities of two ROS scavenging enzymes, superoxide dismutase (SOD) and catalase (CAT), reached peak values (1 685.628 and 37.380 U/g, respectively, P < 0.05). Also, the activities of two lignin synthesis-related enzymes, phenylalanine ammonia lyase (PAL) and 4-coumarate:CoA ligase (4CL), reached peak values (544.697 and 123.221 U/g, respectively, P < 0.05). In the HWT group, the activity of peroxidase (POD) increased continuously, which was significantly higher than those of the control and HWT groups. In conclusion, HAT could induce rapid ROS accumulation and the production of key metabolism-accelerating enzymes involved in the phenylpropane metabolism pathway, promoting the accumulation of total phenols, flavonoid and lignin, thereby accelerating the formation of callus in taro corms.