Plasma membrane proteins from herbicide resistant and susceptible wild oat biotypes
Phelps, Sherrilyn Marie
The wild oat biotype UM1 is resistant to the aryloxyphenoxypropanoate (AOPP) and cyclohexanedione (CHD) classes of herbicides. When this project was initiated, the mechanism of herbicide resistance was unknown, but evidence suggested the possible involvement of plasma membrane proteins in the resistance mechanism. Comparison of membrane protein profiles of untreated resistant (UM1) and susceptible (UM5) plants showed no differences between the two biotypes. However, upon herbicide treatment a membraneassociated protein of 47 kDa was greatly reduced in amounts in the susceptible, but not resistant, biotype. This response was thought to be linked to the resistance mechanism. Further studies showed the resistance mechanism to involve an insensitive form of the target enzyme (acetyl CoA carboxylase), thereby negating the involvement of the plasma membrane protein effects in the resistance mechanism. Further characterization of the 47 kDa protein indicated that is was the large subunit of RUBISCO. The effect of AOPP and CHD herbicides on RUBISCO is not believed to be a secondary mode of action of these herbicides, but is related to the general onset of senescence induced by herbicide treatment in susceptible biotypes. The protein response was also inducible in the resistant biotype by treating with other herbicides to which this biotype was sensitive. Although the differential membrane protein response was not involved as a resistance mechanism, its depletion may be useful for detection of herbicide resistance in weed species.