COMPARATIVE UPTAKE, TRANSLOCATION, AND METABOLISM OF PARAQUAT IN TOLERANT KWANGKYO AND SUSCEPTIBLE HOOD SOYBEAN

The “Kwangkyo” and “Hood” cultivars of soybean [Glycine max (L.) Merr.] are differentially sensitive to the herbicide paraquat. The margin of this intraspecific differential herbicide tolerance is narrow and Kwangkyo is about 10-fold more tolerant to paraquat than Hood soybean. The deposition of epicuticular wax on the surface of the first fully expanded trifoliolate was similar in both soybean cultivars and treatment with 1 mM paraquat did not influence the epicuticular wax content in any cultivar. Seedlings of Kwangkyo and Hood soybean absorbed comparable amounts of radioactivity following exposure to root-applied 14C-labeled paraquat for 24 hr. Most of the absorbed radioactivity remained in the roots of seedlings of both cultivars, but a greater amount of the recovered radioactivity translocated from roots to stems and leaves of the sensitive Hood soybean. Following feeding of the cut ends of their petioles with [14C]paraquat for 12 and 24 hr, excised trifoliolates of Kwangkyo soybean retained a greater portion of absorbed radioactivity in their petioles and translocated a smaller amount of radioactivity into the interveinal regions. By contrast, excised trifoliolates of Hood soybean retained a smaller portion of absorbed radioactivity in their petioles and released a higher amount of absorbed radioactivity into the interveinal regions. Extractable paraquat was not metabolized to any extent by tissues of either of the two cultivars and differential metabolism does not appear to play a role in the observed differential response of Kwangkyo and Hood soybean to paraquat. Overall, the results of the present study suggest that restricted mobility or a delayed release of paraquat into the mesophyll region is a likely basis for the observed tolerance of Kwangkyo soybean to the herbicide paraquat. © 1993 Academic Press, Inc.