At 10.4 mM bentazon treatment, the tolerance index of susceptible (S) inbred corn, line TN89, at one-leaf stage decreased to 27% of that of the control, whereas > 90% of tolerance index of control was maintained in tolerant (T) line LU21. More than fourfold of malondialdehyde (MDA) accumulated in S line within 7 d after treatment (DAT), but only a slight accumulation of MDA was found in T line. 14C-Bentazon application experiment indicated that there was no difference in bentazon absorption between T and S lines. However, bentazon metabolism in T line was more active than that in susceptible TN89. The metabolite, 6-glucose-bentazon in T line rapidly accumulated to the maximum 3 DAT, whereas this conjugate actually decreased in S line. Assay of in vitro activity of bentazon-6-hydroxylase showed that it was decreased in both lines with development and that this activity in T line at two-leaf stage was ca. 50% higher than that in S line. It is suggested that the higher bentazon tolerance in LU21 is primarily associated with an active bentazon metabolism, partially due to a higher bentazon-6-hydroxylase activity coupled with glucosylation.
Nomenclature: Bentazon; corn, Zea mays (L.). #3 ZEAMX.
Additional index words: Hydroxylase, inbred line, Taiwan.
Abbreviations: DAT, days after treatment; HPLC, high-performance liquid chromatography; MDA, malondialdehyde; S, susceptible; T, tolerant; TLC, thin-layer chromatography.