Open AccessKinetic Analysis of Resistance to Paraquat in Conyza
Author(s) -
Yoseph Shaaltiel,
Jonathan Gressel
Publication year - 1987
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.85.4.869
Subject(s) - paraquat , chloroplast , thylakoid , superoxide , photosystem ii , biology , photosystem i , chemistry , biochemistry , enzyme , photosynthesis , gene
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.