Development and growth of parthenogenetic sporophytes of Laminaria japonica

Parthenogenetic sporophytes were obtained from isolated female gametophytes of three strains of Laminaria japonica from China. These sporophytes grew to maturity in the sea, producing spores that all grew into female gametophytes. These female gametophytes give rise to another generation of parthenogenetic sporophytes. Chromosome counts show that sporophytes obtained by fertilization were diploid (2n = c.40), and that the spores they produce were haploid (n = c.20). Nuclei from both somatic and sporangial cells in parthenogenetic sporophytes were haploid. Gametophytes were haploid in all cases. Young sporophytes derived from culture with both female and male gametophytes were diploid, while young sporophytes obtained from female gametophytes derived from parthenogenetic sporophytes showed haploid, diploid or polyploid chromosome numbers. Polyploidy was associated with abnormal cell shapes, and diploid sporophytes had abnormal blade shapes, such as a furcate shape, at a small stage. Apparently, only haploid parthenogenetic sporophytes develop normally and grow to reproductive maturity. Parthenogenetic sporophytes with normal development were shorter and narrower than sporophytes derived by fertilization.