Decreased Rate of Degradation of the D1 Protein in Metribuzin-resistant Photoautotrophic Chenopodium rubrum Cell Cultures

Light-induced degradation of the D1 protein of photoautotrophic cells of metribuzin (mbz)-resistant and -susceptible Chenopodium rubrum cell cultures was investigated. The resistant cell cultures were known to possess different double and triple mutations in the photosystem II D1 protein, and these mutations appear to be the primary basis of the variant herbicide resistance (Schwenger-Erger et al., 1993; Schwenger-Erger, 1999) in addition to several apparent adaptive mechanisms within the resistant cell lines (Thiemann and Barz, 1994 a, b; Barz et al., 1995). Pulse/chase investigations on the degradation rate of the D 1 protein during high light conditions now revealed significantly decreased degradation rates in the low resistant cell lines, whereas the highly resistant cell lines showed only a slight decrease when compared to the wild type cells. Furthermore, in the presence of sublethal doses of metribuzin the half-life time of the D1 protein increased 5-fold in the case of the wild type cells but only about 2–2.5-fold in the case of the resistant cell lines.