Re: what is the function of the pyrenoid in the spirogyra cell?

Hi Chris,

Pyrenoids occur in many of the algae and are associated with the chloroplasts. Some of them are known to contain Rubisco, the enzyme that catalyzes the incorporation of inorganic CO₂ into carbohydrate (Graham and Wilcox, 2000). In these algae, pyrenoids probably function to fix carbon. In other algae, pyrenoids are the sites of carbohydrate (typically starch) storage. Starch and iodine react to produce a deep blue- black color, so staining a thin algal prep with iodine will indicate the presence of pyrenoids.

Spirogyra is a filamentous green alga in which the chloroplast has a characteristic spiral shape. In this photograph, you can see the chloroplast coiling against the outer edge of the cells. The numerous small round blobs along the edges of the chloroplast are the pyrenoids. The larger, faint blobs (they look like out-of-focus regions) that take up most of the volume of the cells in the filaments on the right are the nuclei, which are suspended in the interior of the cells.

If you wish to continue your studies of algae, there are numerous web sites with a lot of information and beautiful photographs. Many of them correspond to university courses in botany, and are a great source for material.

http:// darwin.baruch.cuny.edu/bio1003/algae.html
http:// www.ucmp.berkeley.edu/greenalgae/greenalgae.html
http://www.mbari.org/ ~conn/botany/default.htm

A Google search for "algae" will also turn up a plethora of online sources.

Good luck!

Allison J. Gong
MAD Scientist

Reference:
Graham and Wilcox, 2000. Algae. Prentice-Hall, Inc.