The optical isomers, (R)‐1(α‐methylbenzyl)‐3‐p‐tolylurea ((R)‐MBU) and (S)‐1‐(α‐methylbenzyl)‐3‐p‐tolylurea ((S)MBU), which are analogues of daimuron [1‐(α,α‐dimethylbenzyl)‐3‐p‐tolylurea], a herbicide for Cyperaceae weeds and a safener for paddy rice, exhibited different biological responses. These two physiological properties of daimuron 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 rice seedlings than was (R)‐MBU. (S)‐MBU promoted root growth of rice seedlings, 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 intergenus 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 root growth inhibition in the dark.

Rhizome induction activities of the s-triazines and synthetic cytokinins were measured on Cypeyus seyotinus ROTTB. tuber in the dark. The (R)-enantiomers of 2-a-methylbenzylamino-6-chloro-s-triazine compounds having a small alkyl group at 4-amino moiety stimulated the rhizome induction. Medium sized or long-chain alkylamino groups (butyls to decyl) resulted in decrease in activity. Their (S)-antipodes did not cause the rhizome induction. The racemates substituted with an ethyl or propyl group at the benzylic position of the 2-benzylamino-4-methyl (or ethyl) amino-6-chloro-s-triazines also exhibited a significant rhizome inducing activity. The activity of the methoxy or methylthio derivatives of corresponding chloro-s-triazines that was active on rhizome induction was maintained. An s-triazine ring system was essential for the rhizome induction. Kinetin and synthetic cytokinin compounds, forchlorfenuron [l-(2-chloro-4-pyridyl)-3-phenylurea] and thidiazuron [l-phenyl-3-(l, 2, 3thidiazol-5-yl)urea], significantly stimulated rhizome induction similar to 6-benzylaminopurine (BA).