Role of carbonic anhydrase in photosynthesis and inorganic-carbon assimilation in the red algaGracilaria tenuistipitata

✍ Scribed by Kurt Haglund; Mats Björk; Ziyadin Ramazanov; Guillermo García-Reina; Marianne Pedersén

• Publisher: Springer-Verlag
• Year: 1992
• Tongue: English
• Weight: 881 KB
• Volume: 187
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00201951

✦ Synopsis

The mechanism of inorganic-carbon (Ci) accumulation in the red seaweed Gracilaria tenuistipitata Zhang et Xia has been investigated. Extracellular and intracellular carbonic-anhydrase (CA) activities have been detected. Photosynthetic 02 evolution in thalli and protoplasts of G. tenuistipitata were higher at pH 6.5 than at pH 8.6, where HCO3 is the predominant form of Ci. Dextran-bound sulfonamide (DBS), a specific inhibitor of extracellular CA, reduced photosynthetic 02 evolution at pH 8.6 and did not have any effect at pH 6.5. After inhibition with DBS, 02 evolution was similar to the rate that could be supported by CO2 from spontaneous dehydration of HCO~. The rate of photosynthetic alkalization of the surrounding medium by the algal thallus was dependent on the concentration of C~ and inhibited by DBS. We suggest that the general form of Ci that enters through the plasma membrane of G. tenuistipitata is CO2. Bicarbonate is utilized mainly by an indirect mechanism after dehydration to CO2, and this mechanism involves extracellular CA.