High throughput culture and gametogenesis induction of <Emphasis Type="Italic">Laminaria japonica</Emphasis> gametophyte clones

In anticipation of the application of a new sporeling-raising method using gametophyte clones to Laminaria commercial cultivation in China, techniques of mass culture and gametogenesis induction of L. japonica gametophyte clones were developed, as a mass of fertile gametophytes is a prerequisite for sporeling-raising with the new method. Gametophyte clones which were subjected to fed-batch culture exhibited a classical logistic growth curve. Growth rates decreased gradually after 2 months of culture, and were negatively correlated to cell density. UNOVA also showed that only cell density has a significant effect on the growth of gametophyte clones under the experimental conditions. Based on the dynamics models revealed, a culture strategy only directed at the control of cell density was adopted. By this strategy, a total of 36 kg wet weight from an initial weight of 0.75 kg was achieved after 3 months culture in 100 20-L bottles. The final average density reached 24 g L⁻¹. For the subsequent gametogenesis induction, amplificatory male and female gametophyte clones were cut, mixed and cultured in bottles under the same conditions used in amplification except for a change of photoperiod from continuous irradiance to 10 h light: 14 h dark cycle. Egg discharge occurred 10 days after the mixed culture and increased gradually with the culture duration. Most gametophytes gave rise to sporophytes 20 days after induction. Large-scale culture of gametophyte clones and gametogenesis induction for commercial cultivation in 2003–2005 have been conducted successfully.