Spotlight on photosynthesis in marine plankton

The polar regions are major sites for plankton production. Inger Andersson, a structural biologist at SLU in Uppsala, has previously mapped the structure of Rubisco, a protein (enzyme) needed for photosynthesis. It assists in the process of converting carbon dioxide into carbohydrates.

All organisms that photosynthesise, i.e. plants, bacteria, cyanobacteria and algae, use this enzyme, on land and in the sea.

The conditions for photosynthetic carbon fixation in the sea differ from those on land. Most carbon occurs in the form of water-soluble bicarbonate, which must be converted into carbon dioxide before it can be used for photosynthesis.

Aquatic phytoplankton have developed special microcompartments for this purpose, known as carboxysomes, to which bicarbonate is transported and converted into carbon dioxide, assisted by the enzyme carbonic anhydrase.

The concentration of carbon dioxide may be a thousand times greater inside the microcompartment than in the surrounding cell, which enhances the effect of the photosynthetic enzyme Rubisco.

Inger Andersson’s research team has gathered phytoplankton from Svalbard, and is now making a detailed study of the structure of the carboxysomes and how rubisco and carbonic anhydrase interact.

It is now possible to understand how bicarbonate is transported into the carboxysomes and how carbon dioxide is prevented from leaking out into the surrounding cell.