unstable anthocyanin mutation recovered from tissue culture of alfalfa (Medicago sativa). 1. High frequency of reversion upon reculture

A white-flowered mutant ("WFM") was regenerated from tissue culture of a purple-flowered plant of tetraploid alfalfa (Medicago sativa L.). When WFM was recultured, many regenerated plants (>20%) were purple-flowered. Genetic analysis established that a functional allele, C2, of a locus required for anthocyanin pigmentation was in the simplex condition (C2c2c2c2) in the donor genotype when it mutated to an unstable recessive ("mutable") allele, c2-m4, which is carried by WFM. Tissue culture experiments demonstrated that c2-m4 reverts to function at a high frequency in vitro. Results indicate that reversion occurs early in culture and may be the result of a genome shock associated with callus formation. Reversion also occurs in planta, but at a much lower frequency than in vitro. The c2-m4 allele is transmitted to progeny which revert in tissue culture. Revertant alleles, like the progenitor allele, are stable and are sexually transmitted. The action of a transposable element which is especially active in vitro is suggested.