Bicarbonate uptake via an anion exchange protein is the main mechanism of inorganic carbon acquisition by the giant kelp Macrocystis pyrifera (Laminariales, Phaeophyceae) under variable pH

• Main Authors: Fernández, Pamela A, Hurd, Catriona L, Roleda, Michael Y
• Format: Dataset
• Language: English
• Published: PANGAEA 2014
• Subjects: Alkalinity; total; Aragonite saturation state; Aromoana; Benthos; Bicarbonate ion; Bottles or small containers/Aquaria (<20 L); Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Calculated using SWCO2 (Hunter; 2007); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Carbonic anhydrase activity; standard error; Chromista; Coast and continental shelf; Coulometric titration; EXP; Experiment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Inhibition of net photosynthesis; Laboratory experiment; Macroalgae; Macrocystis pyrifera; Net photosynthesis rate; oxygen; OA-ICC; Ocean Acidification International Coordination Centre; Ochrophyta; Other metabolic rates; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); pH; Potentiometric titration; Primary production/Photosynthesis; Salinity; Single species; South Pacific; Species; Spectrophotometric; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.839919; https://doi.org/10.1594/PANGAEA.839919

Macrocystis pyrifera is a widely distributed, highly productive, seaweed. It is known to use bicarbonate (HCO3-) from seawater in photosynthesis and the main mechanism of utilization is attributed to the external catalyzed dehydration of HCO3- by the surface-bound enzyme carbonic anhydrase (CAext). Here, we examined other putative HCO3- uptake mechanisms in M. pyrifera under pHT 9.00 (HCO3-: CO2 = 940:1) and pHT 7.65 (HCO3-: CO2 = 51:1). Rates of photosynthesis, and internal CA (CAint) and CAext activity were measured following the application of AZ which inhibits CAext, and DIDS which inhibits a different HCO3- uptake system, via an anion exchange (AE) protein. We found that the main mechanism of HCO3- uptake by M. pyrifera is via an AE protein, regardless of the HCO3-: CO2 ratio, with CAext making little contribution. Inhibiting the AE protein led to a 55%-65% decrease in photosynthetic rates. Inhibiting both the AE protein and CAext at pHT 9.00 led to 80%-100% inhibition of photosynthesis, whereas at pHT 7.65, passive CO2 diffusion supported 33% of photosynthesis. CAint was active at pHT 7.65 and 9.00, and activity was always higher than CAext, because of its role in dehydrating HCO3- to supply CO2 to RuBisCO. Interestingly, the main mechanism of HCO3- uptake in M. pyrifera was different than that in other Laminariales studied (CAext-catalyzed reaction) and we suggest that species-specific knowledge of carbon uptake mechanisms is required in order to elucidate how seaweeds might respond to future changes in HCO3-:CO2 due to ocean acidification.