Metribuzin-Resistant Mutants of Chlamydomonas reinhardii

Herbicide resistance in Chlamydomonas reinhardii cells was induced by mutagenesis with 5-fluorodeoxyuridine and ethylmethanesulfonate. Four mutant strains were isolated and analyzed for resistance against DCM U-type or phenolic inhibitors o f photosynthetic electron transport. The mutants were different in both the extent and the pattern o f their resistance: the R /S value, i.e. the ratio o f / 50 values o f the inhibition o f photosynthetic electron transport in isolated resistant and susceptible thylakoids, varied for metribuzin from 10 000 to 36. The mutant MZ-1 was resistant against metribuzin, atrazine and D C M U , whereas the mutant MZ-2 showed resistance mainly against metribuzin and atrazine. The mutant MZ-3 was similar to MZ-1, but showed a lesser extent o f resistance against DCM U. The mutant M Z-4 showed resistance against metribuzin, but not against atrazine. These results demonstrate that the resistance against one herbicide of the DCM U-type (metribuzin) must not be accom panied by similar resistance against te other inhibitors. Binding studies with radioactively labeled herbicides, [ l4C]metribuzin, [HC]atrazine and [3H]DCMU, and isolated thylakoids supported these observations. Phosphorylation o f thylakoid membrane proteins was studied with wild-type cells and resistant mutants under in vivo conditions in the light. The 32P-labeled m ain proteins bands were in the molecular weight range o f 1 0 -1 4 kDa, 2 6 -2 9 kDa, 3 2 -3 5 kDa and 4 6 4 8 kDa. The pattern and the extent o f incorporation o f 32P were similar for the mutants and the wild-type cells.