Plant Growth-promototing Activities of Mercaptriazinone Derivatives

Twenty-nine mercaptotriazinone derivatives were synthesized and their plant growth-promoting activities were examined by the rice (Oryza sativa) seedling test in the presence or absence of gibberellic acid (GA3). For high activity in promoting the GA3-induced shoot elongation, an isopropyl or an appropriately substituted phenyl group, a hydrogen atom and a lower alkyl thio group were required in the 1-, 3-and 4-positions, respectively, of the 1,3,5-triazine-2,6-dione structure. In more detailed experiments, 4-methylthio-1-(p-tolyl)-s-triazine-2,6(1H, 3H)-dione, one of the most potent mercaptotriazinones, was found to synergistically promote the GA3-induced elongation of the first and second leaves of rice seedlings. Several mercaptotriazinone derivatives, active or inactive, in the rice seedling test were examined by the radish (Raphanus sativus) leaf disk expansion test, but all of them were completely inactive. Structure-activity relationships of mercaptotriazinone derivatives are discussed in relation ...