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Plant Physiology 85:869-871 (1987)
© 1987 American Society of Plant Biologists

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Environmental and Stress Physiology

Kinetic Analysis of Resistance to Paraquat in Conyza1

Evidence that Paraquat Transiently Inhibits Leaf Chloroplast Reactions in Resistant Plants

Yoseph Shaaltiel2 and Jonathan Gressel3

Department of Plant Genetics, Weizmann Institute of Science, Rehovot IL76100, Israel

Paraquat resistance has been claimed to be due to a sequestration of the herbicide before it reaches chloroplasts. This is based on the sensitivity of photosystem I in isolated thylakoids to paraquat, and autoradiographic analyses showing label from paraquat near veins 4 hours after treatment of a resistant biotype. Conversely, the enzymes of the superoxide detoxification pathway were found to be at constitutively elevated levels in intact class A chloroplasts of the resistant biotype of Conyza bonariensis (L.) Cronq. Evidence is presented here that physiologically active levels of paraquat rapidly inhibit chloroplast function in both the resistant and sensitive biotype, before the first sequestration was visualized. This inhibition is transient (completed in 2 hours) in the resistant biotype and irreversible in the sensitive type. Intact class A chloroplasts of the resistant biotype with or without paraquat are less susceptible to photoinduced membrane damage than the sensitive biotype without paraquat, as measured by ethane evolution. These data support a hypothesis that the ability to prevent superoxide damage keeps the resistant biotype viable while paraquat or its metabolites are being sequestered.

2 Present address: Department of Biochemistry, University of California, Berkeley.

3 Gilbert de Botton Chair of Plant Sciences.

1 Supported in part by a grant from the Yeda Fund.






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Copyright © 1987 by the American Society of Plant Biologists