Herbicide Resistance and Growth of D1 Ala25i Mutants in Chlamydomonas

Abstract

We elucidated the effects of substituting seven amino acids for Ala at residue 251 of the Chlamydomonas reinhardtii D1 protein on herbicide resistance and photoautotrophic growth. Ala251 has been suggested to play a key role in the structural integrity and function of the stromal loop between transmembrane helices IV and V of D1 and has previously been shown to affect resistance to “classical” PSII specific herbicides. Sensitive and rapid microtiter assays were employed to compare herbicide resistance and photoautotrophic growth in the various mutants. Substitution of Ala251by Ile, Leu or Val conferred resistance to the PSII herbicides atrazine. bromacil and metribuzin but not to DCMU, and impaired photoautotrophic growth in high and low light. Compared to an otherwise isogenic wildtype strain, the lle and Val mutants exhibited nearly identical levels of herbicide resistance and reduced growth while the Leu mutant had even slower growth and higher levels of herbicide resistance. In contrast Cys, Pro, Ser and Gly mutants were phenotypically indistinguishable from wildtype in terms of herbicide sensitivity and photoautotrophic doubling times. Collectively, the seven Ala231mutations differed markedly from an Ala mutant (dr-1) at the well characterized Ser264 D1 residue in terms of herbicide resistance and photoautotrophic growth. © 1997, Verlag der Zeitschrift für Naturforschung. All rights reserved.