Change of the metabolism of glucosinolate in postharvest pakchoi (Brassica rapa L subsp. chinensis) under the condition of red light-emitting diode irradiation
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Abstract:
To investigate the effect of red light-emitting diodes (LED) irradiation on the metabolism of glucosinolates of postharvest pakchoi (Brassica rapa L subsp. chinensis). Firstly, the materials were treated with different conditions of LED irradiation with different color and density. The results showed that the degradation of chlorophyll and the yellowing of pakchoi were inhibited by red LED irradiation with a density of 6.5 μmol/(m2·s). Then, the red LED irradiation with 6.5 μmol/(m2·s) was selected for treating the pakchoi. Then, the changes of glucosinolate content and relative expression level of genes involved in the glucosinolate metabolism of pakchoi after red LED irradiation were analyzed to explored the possible regulatory mechanism of this treatment. The results indicated that the contents of total glucosinolate and isothiocyanate in petiole of pakchoi were 2.72 times and 1.32 times higher than those in leaves, respectively. Additionally, the relative expression of genes including MYB28, CYP83A1, and GSTF11 were up-regulated by the red LED irradiation, thus promoting the synthesis of glucosinolate such as gluconapin. As a result, the content of total glucosinolate in the treated petiole of pakchoi was 1.62~1.99 times higher than that in the control during 4~8 day of storage. The myrosinase activity in the petiole of pakchoi was also promoted by the red LED irradiation, and consequently, the accumulation of total isothiocyanate in the petiole of pakchoi was increased. Notably, the total isothiocyanate contents in the control group were lower by 77.43%~91.98% than those in the red LED irradiation treated group during 4~8 day. In conclusion, the red LED light treatment could delay the losses of glucosinolates and isothiocyanates in pakchoi, which could be explained by the upregulated relative expression level of genes involved in the synthesis of aliphatic glucosinolate and the increased myrosinase activity in the sample.