Clonal propagation of Laminaria digitata (Phaeophyceae) sporophytes through a diploid cell-filament suspension

In vitro cultures of Laminaria digitata (Hudson) Lamouroux stipe medullary explants (Laminariales, Phaeophyceae) gave rise to friable morula-like mass es of pigmented cells. Upon subculture under continuous white light:they gr ew out as filaments, which tended to dissociate into spherical isolated cel ls, leading to the establishment of a suspended cell-filament culture. Depe nding on culture conditions, this cell-filament suspension underwent variou s forms of growth, including regeneration of morphologically normal sporoph ytes, and this developmental pathway was stimulated by blue light, Genotypi ng with nine polymorphic microsatellite markers indicated that the regenera ted sporophytes and the cell-filament suspension shared the same genotype, As assessed by flow cytometric analysis of isolated nuclei, the cell-filame nt suspension exhibited a 2C nuclear DNA content, whereas the regenerated s porophytes displayed a 4C level. Chromosome counting, however, showed that both the mother suspension and the regenerated sporophytes were diploid, su ggesting the involvement of polyteny in the regeneration process.