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. Issue 6 (11th November 2014)

• Record Type: Journal Article
• Authors: Fernández, Pamela A.; Hurd, Catriona L.; Roleda, Michael Y.; Wernberg, T.
• Is Part Of: Journal of phycology. Volume 50:Issue 6(2014:Dec.)
• Page Start: 998
• Page End: 1008
• Publication Date: 2014-11-11
• Subjects: Algae -- Periodicals; 579.8
• DOI: 10.1111/jpy.12247
• Languages: English
• ISSNs: 0022-3646

Abstract

<abstract abstract-type="main" id="jpy12247-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p> <italic>Macrocystis pyrifera</italic> is a widely distributed, highly productive, seaweed. It is known to use bicarbonate (HCO<sub>3</sub><sup>−</sup>) from seawater in photosynthesis and the main mechanism of utilization is attributed to the external catalyzed dehydration of HCO<sub>3</sub><sup>−</sup> by the surface‐bound enzyme carbonic anhydrase (CA<sub>ext</sub>). Here, we examined other putative HCO<sub>3</sub><sup>−</sup> uptake mechanisms in <italic>M. pyrifera</italic> under pH<sub>T</sub> 9.00 (HCO<sub>3</sub><sup>−</sup>: CO<sub>2</sub> = 940:1) and pH<sub>T</sub> 7.65 (HCO<sub>3</sub><sup>−</sup>: CO<sub>2</sub> = 51:1). Rates of photosynthesis, and internal CA (CA<sub>int</sub>) and CA<sub>ext</sub> activity were measured following the application of AZ which inhibits CA<sub>ext</sub>, and DIDS which inhibits a different HCO<sub>3</sub><sup>−</sup> uptake system, via an anion exchange (AE) protein. We found that the main mechanism of HCO<sub>3</sub><sup>−</sup> uptake by <italic>M. pyrifera</italic> is via an AE protein, regardless of the HCO<sub>3</sub><sup>−</sup>: CO<sub>2</sub> ratio, with CA<sub>ext</sub> making little contribution. Inhibiting the AE protein led to a 55%–65% decrease in photosynthetic rates. Inhibiting both the AE protein and CA<sub>ext</sub> at pH<sub>T</sub> 9.00 led to 80%–100% inhibition of photosynthesis, whereas at pH<sub>T</sub> 7.65, passive CO<sub>2</sub> diffusion supported 33% of photosynthesis. CA<sub>int</sub> was active at pH<sub>T</sub> 7.65 and 9.00, and activity was always higher than CA<sub>ext</sub>, because of its role in dehydrating HCO<sub>3</sub><sup>−</sup> to supply CO<sub>2</sub> to RuBisCO. Interestingly, the main mechanism of HCO<sub>3</sub><sup>−</sup> uptake in <italic>M. pyrifera</italic> was different than that in other Laminariales studied (CA<sub>ext</sub>‐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 HCO<sub>3</sub><sup>−</sup>:CO<sub>2</sub> due to ocean acidification.</p> </abstract>