Nuclear DNA content in five Norwegian brown macroalgae

We determined the nuclear DNA content in five common marine brown macroalgae from the Norwegian coast, comprising three representatives of Ectocarpales (Dictyosiphon foeniculaceus, Leathesia marina, Asperococcus bullosus), one representative of Chordales (Chorda filum) and one representative of Laminariales (Alaria esculenta). This study provides the first nuclear DNA content estimates for four of these taxa, thereby expanding the Kew database of unreplicated gametic nuclear DNA content. The three Ectocarpales species exhibited remarkably consistent 1C values of approximately 0.2 pg, independent of thallus morphology (globose, filiform and branched, or irregularly inflated and tubular), while the representatives of Chordales and Laminariales demonstrated significantly higher values of 0.64 pg and 0.62–0.75 pg, respectively. We constructed a phylogenetic tree relating the studied brown algae species to their respective C-values. This suggests that phylogeny, rather than thallus morphology, is the primary determinant of nuclear DNA content. The relationship between age/cell size and nuclear DNA content warrants further investigation, particularly in Laminariales. Brown algae typically exhibit a life cycle that alternates between haploid and diploid phases, which can manifest in varying morphology and size. Additionally, they employ diverse sexual or asexual reproduction strategies and often generate environmentally resistant resting stages. Consequently, the same species may display variations in nuclear content and ploidy throughout its life cycle. Recently, ploidy manipulation in brown algae has gained attention among breeders and cultivators for its potential application in aquaculture, like its established use in terrestrial plants. However, our understanding of ploidy dynamics within different brown algal lineages remains limited. Phylogeny, rather than thallus morphology, determines nuclear DNA content in Ectocarpales.In Laminariales, thallus differentiation and plant size are linked to nuclear DNA content.First nuclear DNA content estimate for a Chordales species and three new C-value estimates for Ectocarpales. Phylogeny, rather than thallus morphology, determines nuclear DNA content in Ectocarpales. In Laminariales, thallus differentiation and plant size are linked to nuclear DNA content. First nuclear DNA content estimate for a Chordales species and three new C-value estimates for Ectocarpales.