The induction of the CO2-concentrating mechanism is correlated with the formation of the starch sheath around the pyrenoid of Chlamydomonas reinhardtii
The pyrenoid is a prominent proteinaceous structure found in the stroma of the chloroplast in unicellular eukaryotic algae, most multicellular algae, and some hornworts. The pyrenoid contains the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase and is sometimes surrounded by a carbohydrate sheath. We have observed in the unicellular green alga Chlamydomonas reinhardtii Dangeard that the pyrenoid starch sheath is formed rapidly in response to a decrease in the CO2 concentration in the environment. This formation of the starch sheath occurs coincidentally with the induction of the CO2-concentrating mechanism. Pyrenoid starch-sheath formation is partly inhibited by the presence of acetate in the growth medium under light and low-CO2 conditions. These growth conditions also partly inhibit the induction of the CO2-concentrating mechanism. When cells are grown with acetate in the dark, the CO2-concentrating mechanism is not induced and the pyrenoid starch sheath is not formed even though there is a large accumulation of starch in the chloroplast stroma. These observations indicate that pyrenoid starch-sheath formation correlates with induction of the CO2-concentrating mechanism under low-CO2 conditions. We suggest that this ultrastructural reorganization under lowCO2 conditions plays a role in the CO2-concentrating mechanism C. reinhardtii as well as in other eukaryotic algae. © 1994 Springer-Verlag.
Publication Source (Journal or Book title)
Ramazanov, Z., Rawat, M., Henk, M., Mason, C., Matthews, S., & Moroney, J. (1994). The induction of the CO2-concentrating mechanism is correlated with the formation of the starch sheath around the pyrenoid of Chlamydomonas reinhardtii. Planta, 195 (2), 210-216. https://doi.org/10.1007/BF00199681