Adaptation of Chlamydomonas Reinhardtii to Limiting CO2 Conditions
The unicellular green alga Chlamydomonas reinhardtii can adapt to limiting CO2 conditions through the action of a CO2 concentrating mechanism (CCM). When grown on elevated CO2 (10 to 100 times ambient levels of CO2), C. reinhardtii exhibits relatively poor affinity for external inorganic carbon. However if cells grown on elevated CO2 are switched to low CO2 conditions (ambient levels of C2 the alga will adapt to the limiting CO2 environment within four hours. During this adaptation a number of new proteins are synthesized and significant morphological changes occur. We have found that over 90% of the Rubisco within the cell is localized to the pyrenoid when cells are grown on low CO2 conditions. In contrast, in cells grown on elevated CO2 a majority of the Rubisco (60%) is found in the chloroplast stroma. In addition to the redistribution of Rubisco, messages encoding three isoforms of carbonic anhydrase, a cyclophilin and three novel membrane proteins increase under low CO2 conditions. The sequence of one of these novel cDNAs named lci2, will be reported here.
KeywordsCO2 concentrating mechanism Chlamydomonas gene regulation pyrenoid
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