Porphyra, Commonly Known As Nori or Kim

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Porphyra, commonly know as nori, is the most widely consumed seaweed in the world! It's commonly found in Asian food, especially Japanese food, which has lead to the huge nori industry in Japan. With a very interesting heteromorphic life history, Porphyra has just everything you would want in an alga!

Porphyra Taxonomy

• Kingdom: Protista
• Division: Rhodophyta
• Class: Rhodophyceae
• Subclass: Bangiophycidae
• Order: Bangiales
• Family: Bangiaceae

As a result of Porphyra's heteromorphic life history, the sporophyte stage of Porphyra was originally thought to be a separate alga called Conchocelis rosea. It was not until 1949 did scientists realize that Conchocelis rosea was actually a life history stage of Porphyra.

Porphyra Chemistry

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Pigments

The pigments in Porphyra are as follows:

• Chlorophyll a
• Phycobilins - phycoerythrin and phycocyanin

Chlorophyll a is used for photosynthesis, and the green color is sometimes masked by phycoerythrin, which contributes the "red" to the red algae. Many of the red algae do not have a reddish-color as a result of photodestruction of phycoerythrin. Phycocyanin generally reflects a bluish color. The phycobilins are located in phycobilisomes, which can be found on the outer surfaces of thylakoids.

Storage

The primary storage form for Porphyra is by starch.

Cell Wall

The cell wall of Porphyra is remarkable in many ways. The outermost cuticle is made of protein, with an outer amorphous compartment made of mucilage or slime. Inside is a rigid compartment made of microfibrils. There has been mannan found in some species of Porphyra.

Porphyra has the remarkable capacity for survival against dessication and can dry out for days without harm. This is a result of the cell wall. The ability to withstand dessication is also useful for transmitting spores once the thallus is remoistened.

Click here to learn about the effects of light on the reproductive cycle!

Click here to learn about why heteromorphic life histories exist!

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.

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