Suppressive Effects of Coumarins on Pumpkin Seedling Growth and Glutathione S-Transferase Activity

The effects of some coumarins (coumarin, 7-hydroxycoumarin, scopoletin and esculetin) were investigated on pumpkin (Cucurbita maxima Duch.) seedlings and on pumpkin glutathione S-transferases (GSTs). Coumarin and esculetin suppressed the growth of seedlings, especially the elongation of roots as well as hypocotyls. Among the compounds tested, only esculetin inhibited the activity of a particular pumpkin GST by 50%, CmGSTU3 toward 1-chloro-2, 4dinitrobenzene (CDNB) and at a concentration of 22 μM. Both ethylacetae (EtOAc) and water fractions in pumpkin seedlings and different organs of one-month-old pumpkin plants contained esculetin or similar hydrophobic fluorescent substances as well as hydrophilic substances, which showed different degrees of inhibitory effects on CmGSTU3 activity.