Influence of Drought Stress Treatment on Saponarin Content during the Growing Period of Barley Sprouts

BACKGROUND: Barley sprouts contain a large number of secondary metabolites such as polyphenols, saponarin, and policosanols. The synthesis of such secondary metabolites occurs as a defense mechanism against external environmental stresses. In particular, it has been widely known that drought stress (DS) increases the content of flavonoids in plants. The objective of this study was to investigate the effects of drought stress treatment on the saponarin content in barley sprouts during the growing period. METHODS AND RESULTS: In this study, changes in saponarin content with different DS exposure periods and times were evaluated under the hydroponic system. For establishing different DS treatment periods, water supply was stopped for 1, 2, and 3 days, once leaf length was at 10 cm. To control different DS treatment times, water supply was stopped for 2 days, once leaf lengths were 5, 10, and 15 cm. As a result, the water potential of barley sprouts decreased from -0.8 MPa (before DS treatment) to -1.2, -2.4, and -3.2 MPa (after DS treatment), and reversely recovered to -0.8 MPa after re-irrigation. When 10 cm leaves were subjected to DS for 1 and 2 days, the saponarin content increased by 12 and 10%, respectively, while it increased by 19% when DS was applied to the 5 cm leaves. CONCLUSION(S): The results of this study suggest that drought stress at the early stage of growth (5 cm) is most helpful to increase the saponarin content of barley sprouts.