Photosynthetic performance and antioxidant metabolism in a paraquat-resistant mutant of Chlamydomonas reinhardtii L.

A paraquat-resistant mutant was isolated from photomixotrophic cultures of Chlamydomonas reinhardtii, which showed a factor of resistance of 76.5 in l ight and 107 in dark compared to the WT cultures. When treated with eightfo ld higher concentrations of paraquat, this paraquat-resistant mutant showed inhibition of photosynthetic oxygen evolution and F-v/F-o ratios similar t o those of WT. Exclusion of paraquat from the target site could be responsi ble for the expression of this resistance. The constitutive levels of antio xidant enzymes were similar in WT and paraquat-resistant cultures. However, the levels differed when the cultures were treated with paraquat. The para quat-resistant mutant showed similar increases in the levels of antioxidant enzymes when grown in light or dark, which could possibly be attributed to the cytosolic or mitochondrial isoforms of these enzymes. Expression of re sistance may occur due to exclusion of paraquat and/or detoxification of pa raquat-generated active oxygen species by the antioxidant enzymes. (C) 1999 Academic Press.