Abstract
Biological activity and fate of metazachlor were compared in cell suspension cultures and seedlings from rice and spinach. Growth of cell cultures was not (rice) or only slightly (spinach) inhibited by 200μM and 100μM metazachlor, respectively. In contrast, seedling growth was halved with 50nM metazachlor (rice) and 35% less with 100μM (spinach). In rice seedlings, 0.1μM metazachlor significantly decreased fatty acid desaturation, while 100-200μM had little or no effect in the other 3 systems. Cell suspension cultures weree more tolerant to metazachlor than the corresponding plant systems. Uptake could not explain tolerance since it was lowest in the most sensitive system (rice seedlings). All systems were able to metabolize metazachlor. After 72hr spinach cell culture and seedlings fed with 200μM metazachlor still contained 3.3 and 48μM parent herbicide, respectively. ice seedlings incubated with 0.1μM herbicide contained only 18nM of parent metazachlor after 24hr. 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.
