Keywords: chalcone, naringenin, plant growth.Hence, we propose that the lignin biosynthesis pathways involving 4CL might have the potential as novel action sites of plant growth suppression in selected species. The objective of the present study was to investigate the sensitivity of a wide range of annual plant species to naringenin and chalcone. Compounds and plantsNaringenin (4¢-, 5-, 7-trihydroxyflavanone, 95%) and chalcone (1,3-diphenyl-2-propen-1-one, 97%) were commercially obtained from Sigma-Aldrich Co. (Tokyo, Japan) and Acros Organics Co. (Tokyo, Japan), respectively. Twenty annual species (Table 1), which cover 10 families, were evaluated for their responses to naringenin and chalcone. Crop seeds were purchased from Sakata Seed Co. Ltd. (Yokohama, Japan). Weed seeds of common chickweed (Stellaria media Villars), great burdock (Arctium Lappa L.) and early watergrass (Echinochloa oryzicola Vasing) were obtained locally from our laboratory. Crop and weed species were evaluated and their respective scientific and family names are listed in Table 1. Plant growth and compound treatmentsSeeds were rinsed with distilled water four times and germinated in tissue culture dishes (F100 mm) containing wet muslin in the growth chamber in darkness at 30∞C for 48 h. The germinated seedlings were grown on wet muslin in plastic plates (200 ¥ 300 mm) containing nutrient solution (1/1000 of Hyponex, Type: 5-10-5 [N : P : K = 10 : 10 : 5%], Hyponex, Japan) in a greenhouse under natural light at about ±25∞C. At the second-leaf stage, the seedlings were transferred into bottles (200 mL) and sponge was used to support the seedlings so that the roots were exposed to Hyponex nutrient solution with (i.e. treatment) or without (i.e. control) 0.1 mmol L -1 naringenin or chalcone (final concentra-