Changes in Glucosinolate Metabolism in Postharvest Pakchoi (Brassica rapa L subsp. chinensis) under Red Light-emitting Diode Irradiation
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Abstract:
Light-emitting diode (LED) irradiation with different colors and densities was employed for investigating the effect of red light on glucosinolate metabolism in postharvest pakchoi (Brassica rapa L subsp. chinensis). The results showed that both chlorophyll degradation and pakchoi yellowing were inhibited by red LED irradiation at a density of 6.5 μmol/(m2•s). Subsequently, the changes in glucosinolate content and relative expression level of genes involved in the glucosinolate metabolism of pakchoi after red LED irradiation (6.5 μmol/m2•s) were analyzed to explore the underlying regulatory mechanism. The results indicated that the contents of total glucosinolate and isothiocyanate in pakchoi petiole were 2.72 and 1.32 times higher than those in leaves, respectively. Additionally, the expression of key aliphatic synthesis genes, including MYB28, CYP83A1, and GSTF11, was significantly upregulated by red LED irradiation, thus promoting the synthesis of glucosinolate such as 3-butenyl glucosinolate. Consequently, the total glucosinolate content in treated pakchoi petiole was 1.62~1.99 times higher than that in the control during 4~8 d of storage. The myrosinase activity was promoted, and consequently, the accumulation of total isothiocyanate was increased in pakchoi petiole following red LED irradiation. Notably, the total isothiocyanate content in the control group was 77.43%~91.98% lower than that in the irradiated group during 4~8 d. In conclusion, red LED light treatment delayed the loss of glucosinolates and isothiocyanates in pakchoi, as indicated by the upregulated relative gene expression levels involved in the synthesis of aliphatic glucosinolate and increased myrosinase activity.
