2-PHENYL-5H-PYRAZOLO[5,1-A]ISOQUINOLIN-5-ONES - DEVELOPMENT OF NEW AUXIN TRANSPORT INHIBITORS AND THEIR PLANT-GROWTH REGULATING PROPERTIES

2-Phenylisoxazolylphenylacetic acids (isoxazoles) and 2-phenyl-5H-pyra zolo[5,1-alpha]isoquinolin-5-ones (isoquinolines) inhibited auxin pola r transport (ATP) and inhibited hypocotyl elongation in the same conce ntration as benzoic acid APT inhibitors, known as phytotropins. At ear ly growth stages of rice, tomato, cucumber, and soybean, isoquinolines inhibited stem elongation in a lower concentration than isoxazoles tr iiodobenzoic acid and 2-phenylisoxazolylbenzoic acid (phytotropin). p- OMe, F, Br, or CF3 substituent on isoquinoline increased the growth in hibiting activity in rice stem, whereas m-Cl, F, or m,p-DiOMe substitu ents increased the activity in soybean. In fields, p-F isoquinoline ha d more favorable properties than the other isoquinolines and structura lly related compounds such as m-Cl isoxazole and DPX-1840 (phytotropin ) in that it (25 g ha(-1)) sometimes increased seed yields of rice and wheat. The early morphological changes due to apical dominance inhibi tion, increase of tiller or branch number, and reduction of plant heig ht were observed on various rice cultivars of Japonica and Indica, whe reas they seem not to be concerned with seed yield.