Glucosinolate content in the leaf stage and leaf position of pakchoi

Glucosinolate, an important plant secondary metabolite with many biological activities, is closely related to human life. To study the change of glucosinolate content in different leaf stages and leaf positions of pakchoi, an experiment was carried out on pakchoi 'Heiyoudong' as test material. Using a solid-phase extraction instrument and high performance liquid chromatograph, glucosinolate content in the four-leaf, eight-leaf, and twelve-leaf stages as well as in leaf positions for the eight-leaf stage, was measured. Results showed that total glucosinolate content in the eight-leaf stage of pakchoi was higher (P < 0.05) than that in the four-leaf and twelve-leaf stages. Also, the content of aliphatic glucosinolates decreased (P < 0.05) with an increase in leaf stage. Changes of indoles and aromatic glucosinolates were consistent with changes of total glucosinolates. Total glucosinolate content at the inner leaf position was higher than the outer leaf position with the central part having the highest glucosinolate content of 4.35 μmol·g-1; aliphatic glucosinolate was up to 2.55 μmol·g-1; indole glucosinolate was as high as 1.60 μmol·g-1; and aromatic glucosinolate was relatively low. In addition, indole glucosinolate of Y7 (seventh leaf from top to bottom) accounted for the highest proportion in total glucosinolates (56.7%). Other leaves (except Y7) were dominated by aliphatic glucosinolates accounting for 59.0%-79.0% of the total glucosinolate. Among all the leaf positions, the content of aromatic glucosinolates was the lowest (P < 0.05) accounting for less than 7.1%. This study explored the distribution of glucosinolates in pakchoi and could provide a reference for research on plant stress resistance.