EFFECT AND METABOLISM OF THE CHLOROACETAMIDE HERBICIDE METAZACHLOR - COMPARISON OF PLANT-CELL SUSPENSION-CULTURES AND SEEDLINGS

Biological activity and fate of metazachlor were compared in cell susp ension cultures and seedlings from rice and spinach. Growth of cell cu ltures was not (rice) or only slightly (spinach) inhibited by 200 mum and 100 mum metazachlor, respectively. In contrast, seedling growth wa s halved with 50 nM metazachlor (rice) and 33% less with 100 muM (spin ach). In rice seedlings, 0.1 mum metazachlor significantly decreased f atty acid desaturation, while 100-200 mum had little or no effect in t he other 3 systems. Cell suspension cultures were more tolerant to met azachlor than the corresponding plant systems. Uptake could not explai n tolerance since it was lowest in the most sensitive system (rice see dlings). All systems were able to metabolize metazachlor. After 72 hr spinach cell culture and seedlings fed with 200 muM metazachlor still contained 3.3 and 48 muM parent herbicide, respectively. Rice seedling s incubated with 0.1 mum herbicide contained only 18 nm of parent meta zachlor after 24 hr. This low but still very phytotoxic concentration of parent metazachlor in rice seedlings compared with the high and yet non-toxic concentration found in spinach suggests that metabolism via glutathione conjugation might not be the only protection mechanism in tolerant plants.