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Differential Accumulation of Protoporphyrin IX between Oxyfluorfen Resistant and Non-Resistant Soybean Cell Lines
Eiji WARABI, Kenji USUI and Hiroshi MATSUMOTO
J. Pestic. Sci.
27, 106-110 (2002)
The diphenyl ether herbicide oxyfluorfen causes an accumulation of protoporphyrin IX (Proto IX) in plants as a result of the inhibition of protoporphyrinogen oxidase (Protox). We previously reported that an oxyfluorfen-resistant soybean cell line selected by a stepwise selection method grew normally under 10(-7) M oxyfluorfen due to the overproduction of mitochondrial Protox. In the present study, the accumulation and localization of Proto IX in normal and resistant cells after treatment with oxyfluorfen were examined by spectrofluorometry and fluorescence microscopy. The normal cells accumulated great amounts of Proto IX in the presence of 10(-6) and 10(-7) M oxyfluorfen whereas the resistant cells accumulated much less. The level of Proto IX reached a maximum at 4 to 8 hr after treatment under illumination and then gradually decreased. In the dark, the Proto IX content increased linearly until 24 hr and fluorescence from Proto IX was detected in cytoplasm and plasma membrane in the oxyfluorfen-treated normal cells. In resistant cells, chlorophyll autofluorescence was detected in non-treated cells, and Proto IX fluorescence was not detectable. This autofluorescence, however, disappeared with 10(-7) M oxyfluorfen treatment. These results strongly support that the overproduction of mitochondrial Protox is responsible for the resistance to oxyfluorfen in this selected soybean cell line.
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