THE INDUCTION OF BIOCHEMICAL AND MORPHOLOGICAL MUTANTS IN THE MOSS PHYSCOMITRELLA PATENS

Physcomitrella patens is a monoecious, cleistocarpous moss which completes its life cycle under defined conditions in 7 to 8 weeks. Sexual reproduction is readily obtained by culturing gametophytes at 15 to 19 C. Mutants were induced by treatment of either spores or protonemal cells with ethyl methane sulfonate, N‐methyl‐N'‐nitro‐N‐nitrosoguanidine and X‐rays. Thiamine, para‐aminobenzoic acid, niacin and yeast extract auxotrophs were obtained. Growth response to various supplements was studied in the auxotrophic mutants. Five yellow mutants and two morphological mutants were induced. The chlorophyll content of the yellow mutants is reduced 35‐65% of wild type. The self‐sterile, para‐aminobenzoic acid‐dependent mutant was used as the archegonial parent in crosses with a yellow mutant and a morphological mutant. The self‐sterility of the para‐aminobenzoic acid‐requiring mutant appears to be pleiotropically related to the auxotrophic condition, since self‐sterility does not segregate from nutritional dependence in progeny of crosses. On the basis of tests with heterozygous diploids obtained by aposporous regeneration of capsule cells, two mutant alleles were shown to be recessive to their respective wild‐type alleles.