Herbicide Resistant Weeds

Mechanism of paraquat tolerance in Conyza bonariensis and in Lolium perenne.

Shaaltiel, Y. and J. Gressel. 1985. Mechanism of paraquat tolerance in Conyza bonariensis and in Lolium perenne. Phytoparasitica. 13: 232.

A resistant biotype of C. bonariensis from the Tahrir irrigation district survived 100-fold higher paraquat levels than the wild type. This biotype showed some cross resistance to both oxyfluorfen and SO2, supporting a theory that resistance is due to ability to detoxify oxygen radicals, particularly those developing in the chloroplast. Chloroplast enzyme activities were therefore studied for possible detoxifying effects following interaction of paraquat with photosystem I. Superoxide dismutase levels in total leaf extracts were similar in sensitive and resistant plants while levels in intact chloroplasts showed a 50% increase; glutathione reductase levels were 100% higher and ascorbate peroxidase was 150-200% higher. The increase in superoxide dismutase activity was in a single isoenzyme. In strain PRP-16 of Lolium perenne showing tolerance to 30-fold higher paraquat concn. than the wild biotype, 2 extra superoxide dismutase isoenzymes were present.