This mutation was induced by X-rays and selected for its tolerance to the herbicide paraquat. Paraquat is a broadly effective herbicide that acts rapidly in full sunlight by accepting an electron from Photosystem I which results in production of the highly reactive superoxide anion. This free radical causes extensive damage to membranes and results in rapid bleaching and desiccation of plants exposed to light. In C-Fern, this is a recessive mutation that is expressed in both gametophytes and homozygous sporophytes. Tolerance is very clear-cut and it is quite easy to identify tolerant individuals from sensitive wild type individuals. However, in contrast to glyphosate, paraquat is toxic to humans and many wildlife. Currently, its use and availability are restricted. It can be obtained for research purposes under the name methyl viologen or paraquat dichloride. The wild type and pq45 can be clearly distinguished by assay of gametophyte growth on nutrient agar or sporophyte leaf bleaching in distilled water at a concentration of 0.5 mM paraquat. Available only in a double mutant herbicide-tolerant line with glt1.

Carroll, E. W., O. J. Schwarz and L. G. Hickok. 1988. Biochemical studies of paraquat-tolerant mutants of the fern Ceratopteris richardii. Plant Physiol. 87: 651-654.

Hickok, L. G. and O. J. Schwarz. 1986. Paraquat tolerant mutants in Ceratopteris: Genetic characterization and reselection for enhanced tolerance. Plant Science 47: 753-758.