Mild Water Deficit Increases the Contents of Bioactive Compounds in Dropwort

The objective of this study was to determine the effects of mild water deficit on the contents of bioactive compounds in dropwort (Oenanthe stolonifera). Dropwort plantlets with 2-3 offshoots were transplanted into plastic pots containing horticultural growing medium. The plantlets were grown at 22℃ under a relative humidity of 60%, photosynthetic photon flux density (PPFD) of 285 micromolㆍm -²ㆍs -¹, 12-hour light period, and CO2 concentration of 600 μmol·mol-1 and subirrigated with nutrient solution for 3 weeks after transplanting. To induce mild water deficit, we placed wick culture systems (4- and 6-cm long wicks) between the bottom of each pot and the water surface at 3 or 4 weeks after transplanting. The control plants were subirrigated at the pot bottom without wick treatment. The soil water content of plants under water-deficit averaged 45% lower than that of the control at 5 weeks after transplanting. Moreover, mild water-deficit treatment reduced the leaf water potential by 7-25% compared to the control. However, mild water-deficit treatment did not significantly affect the fresh or dry weights of dropwort shoots at 6 weeks after transplanting. All treatments significantly inhibited the photosynthetic rate at 5 weeks after transplanting. In particular, water-deficit treatment using a 6-cm long wick for 2 weeks resulted in a 16% lower photosynthetic rate than that of the control. The total phenolic content and antioxidant capacity of dropwort stems did not significantly differ between treatments. However, in the leaves, total phenolic content and antioxidant capacity of all plants subjected to water-deficit treatments averaged 43 and 64% higher, respectively, than those of the control. The total anthocyanin content in all treatment groups, except for treatment with a 4-cm wick at 4 weeks, was significantly higher than that of the control. These results suggest that dropwort plants subjected to mild water deficit effectively accumulate antioxidant phenolic compounds, including anthocyanins, which is more reminiscent of reddish, small dropwort plants that grow under limited water conditions than of water dropwort.