Artificial production of regenerable free cells in the gametophyte of Porphyra pseudolinearis (Bangiales, Rhodophyceae)

A dioecious red alga, Porphyra pseudolinearis, which does not produce asexual spores such as archeospore, is a commercially valuable Porphyra seaweed. We obtained a large amount of regenerable free cells of P. pseudolinearia by gentle homogenization in seawater after culturing the thalli in nutrient-rich medium with 10 mM of allantoin at 15 °C and 20 °C. The obtained free cells were divided into three forms: globular, elliptic and 2-celled. These free cells formed cell walls slowly compared to conchospores, and they directly developed to thalli or filamentous germlings like conchocelis or conchosporangia. In particular, the occurrence of thalli was remarkable in free cells obtained from the thalli cultured with 10 mM allantoin at 20 °C. Once the free cells developed to the thalli, they showed the same rates of growth to the thalli generated from conchospores, and they grew to be more than 50 cm in blade length. This technique to produce regenerable free cells from the Porphyra species that do not produce archeospores is useful for vegetative propagation and breeding.