2.1. Structure-Activity Relationships among the YCZ-Series with Regard to the Retardation of the Plant Height in Rice
Table 1. Biological effects of YCZ-series analogues on the growth of rice seedlings.
The chemical structures of the compounds are listed in Table 1. In our assays, we used hydroponic methods to culture the rice seedlings and evaluate the biological activity of the analogues of YCZ-series [16]. The common phenotypes of BR deficient mutants of rice plants are characterised by different degrees of dwarfism with erect leaves [6]. We chose plant height as a factor for the evaluation of the biological activity of the test compounds on rice seedlings. Another assay method that is known to be very sensitive to the levels of BR in rice is based on the determination of the bending angle of the
lamina joint of the rice seedlings. The rice lamina joint is a tissue that is found between the leaf blade (leaf lamina) and the leaf sheath that acts similar to a hinge to bend the leaf blade. The bending angle of the lamina joint is sensitive to BR [17]. Furthermore, BR biosynthesis-deficient mutants of rice plants exhibit erect leaves with small bending angles of the lamina joint [18–20]. Thus, determination of the bending angle of the lamina joint of chemically treated rice plants is a straightforward approach to speculate the effects of the compounds used in this study on BR biosynthesis inhibition.