INTERACTION BETWEEN OPTICAL ISOMERISM AND PLANT PHARMACOLOGICAL ACTION, CHANGE OF MODES OF ACTION AND CHIRALITY OF 1-(ALPHA-METHYLBENZYL)-3-P-TOLYLUREA

The optical isomers, (R)-1-(alpha-methylbenzyl)-3-p-tolylurea ((R)-MBU ) and (S)-1-(alpha-methylbenzyl)-3-p-tolylurea ((S)-MBU), which are an alogues of ron[1-(alpha,alpha-dimethylbenzyl)-3-p-tolylurea], a herbic ide for Cyperaceae weeds and a safener for paddy rice, exhibited diffe rent biological responses. These two physiological properties of daimu ron were observed separately in (R)-MBU and (S)-MBU. Only (R)-MBU had herbicidal activity against Cyperaceae weeds, while the (S)-isomer was a more effective safener against bensulfuron-methyl (BSM) injury of r ice seedlings than was (R)-MBU. (S)-MBU promoted root growth of rice s eedlings, but the (R)-enantiomer inhibited root growth. (S)-MBU was a more potent inhibitor than (R)-MBU on PS II reaction of spinach broken chloroplasts. Furthermore, (S)-MBU and (R)-MBU showed cross intergenu s selective phytotoxicity among the Gramineae plants, Oryza sativa L. (rice, cv. Tsukinohikari, japonica), Triticum aestivum L. (wheat, cv. Norin No. 61) and Echinochloa crusgalli var. frumentacea Wight, on roo t growth inhibition in the dark.