THE LIFE-CYCLE OF PORPHYRA TENERA IN VITRO

¹ Haskins Laboratories, 305 East 43rd Street, New York 17, N. Y.

1. The complete life-cycle of Porphyra tenera was obtained in vitro.

2. Chemically defined media or enriched sea water permit good growth of these unialgal (not bacteria-free) cultures.

3. Under suitable light and temperature, the complete life-cycle is completed in 5-6 months. Both the Conchocelis and the thallus phases may be grown out of season.

4. The Conchocelis phase grows well free in liquid media; a calcareous substrate is unnecessary. Conchocelis colonies grown in liquid media when free-floating, are stellate and round, but mold-like when attached to glass walls. They are brown-black or purple-red, depending on the composition of the medium. Rapid and abundant growth of the free Conchocelis is elicited by high-light intensities. Fluorescent light is a good light source.

5. Monosporangia formation and release of fertile monospores are induced by short-day conditions (8-11 hours daily); monosporangia and germinating monospores develop after 1-2 months from the inoculation of the Conchocelis filaments. In continuous light, Conchocelis growth is rapid but the sporangia produced are somehow different from the ones produced in short-day conditions.

6. In continuous light, the number of colonies increases rapidly after transfer to new media. This could be due to formation of new colonies from small pieces of filaments. However, even though free spores were not found, it is not excluded that new Conchocelis colonies may have been derived from special spores.

7. The Conchocelis phase was cultured for one year by transferring free Conchocelis colonies or pieces of filaments every two months in new media. Mass cultures with good yields were obtained in continuous fluorescent light.

8. The leafy thallus, derived from monospores grown in shells, grows well and normally in artificial media, at 13-18° C. and in high intensity incandescent light of 8-11 hours daily, but not in fluorescent light.

9. A photoperiod of 13 hours daily inhibits growth of young thalli (1-2 mm.). The thalli became thick, curly, degenerate, assume a callus appearance, bleach almost completely except for scattered groups of dark-pigmented, big cells which produce spores germinating into Conchocelis filaments. In one type of enriched sea water (SWII), the thalli, after thickening, and while degenerating, produce rhizoid-like structures which give rise to Conchocelis filaments.

10. In nature, the Conchocelis phase grows in the long-day seasons, the leafy thallus phase grows in the short-day seasons; and the transition between the two phases is almost exactly at the equinox. On the contrary, no correlations exist between temperature and the phases of the life-cycle: a large temperature zone (7-21° C.) is common to the two phases. Similarly, our preliminary experiments show that the length of the photoperiod has remarkable effects on the Conchocelis and leafy-thallus phases of P. tenera. The photoperiod governs, besides growth, the formation of the spores producing the next phase of the life-cycle. It is reasonable, therefore, to suppose that like land plants, some sea weeds, or phases of their life-cycle, may be long- or short-day plants.