Photoperiodic Effects on the Life History of Porphyra
Production of conchosporangia in the Conchocelis stage is often under photoperiodic control.
In summary, here are the effects that light has on the life history of Porphyra:
Porphyra torta is found high on the rocky intertidal regions on Puget Sound in Washington. The thallus stage experienced the fastest growth at 12-15 degrees Celsius, which is the temperature that the alga would be exposed to during the summer months in Washington. After formation of the carposporophyte by the fusion of carpogonia and spermatia, the carpospores would be released. Approximately 30-60 days after carpospore germination, the Conchocelis stage would begin producing conchosporangium, or fertile cell rows. The formation of conchosporangia in some species requires a specific environmental stimulus, such as a short day photoperiod, such as P. tenera. However, in other species, such as P. miniata, P. linearis, P. angusta, and P. torta, no environmental stimulus is required for conchosporangium production.
The effects of photoperiod are also crucial in the release of conchospores from the Conchocelis stage. In Conchocelis grown under long day conditions (16L:8D), there was never any release of conchospores, while conchospores were always released under short day conditions(8L:16D). The critical period for conchospore release was determined to be slightly less than 12 hours of light, meaning that the dark period must be greater than 12 hours to induce conchospore release. Therefore, the release of conchospores from the Conchocelis stage occurs in the autumn months, where the days are shorter and the temperatures are colder. The first appearance of the thallus stage occurs in the mid-winter months, in accordance to the fall release of the conchospores.
It has also been noticed that all algae with genuine photoperiodic responses have heteromorphic life histories. The response to photoperiod may have evolved as a result to ensure survival in a volatile environment. One phase may not be able to endure the winter months, while the other can.Reference:
Waaland, JR., Dickson, LG., Carrier, JE., Conchocelis growth and photoperiod control of conchospore release in Porphyra torta (Rhodophyta), Journal of Phycology, 23, 406-414
© 1999 Lisa Chen. All rights reserved. Use for educational purposes permitted with acknowledgment and notice.