Effects of inorganic carbon concentration and pH on carbonic anhydrase activity of gametophytes of Saccharina japonica

Abstract

Carbonic anhydrase (CA) was considered to be an important component of carbon concentrating mechanism (CCM) of algae. It was an inducible enzyme. Environmental factors, especially dissolved inorganic carbon and pH, were known to affect CA activity. Effects of inorganic carbon (CO2 and HCO3−) and pH on CA activity of gametophytes of Saccharina japonica were evaluated in this study. Under high-CO2 condition (3% CO2), the activity of external CA (CAext) was significantly decreased (P < 0.05) from 33.92 REA/g FW to 27.69 REA/g FW. In contrast, the internal CA (CAint) and total CA activities were elevated significantly (p < 0.01) from 36.83 REA/g FW to 48.80 REA/g FW, and from 70.75 REA/g FW to 76.49 REA/g FW, respectively. Addition of an appropriate concentration of HCO3− to the medium, CAint and total CA activities were promoted significantly, although the activity of CAext was inhibited significantly (P < 0.05). In higher HCO3− concentration (up to 1680 mg/L), the activity of CAint was promoted to 60.81REA/g FW, which was twice that of the control. Higher activities of CAint and total CA were induced at low pH. At pH 6.0, the highest activities of CAint (110.85 REA/g FW) and total CA (128.17 REA/g FW) were induced. However, at pH 9.0, the activities of CAint and total CA were reduced to the lowest of 23.31REA/g FW and 42.19 REA/g FW, respectively. This is the first report about the successful detection of CAext activity of gametophytes of S. japonica. The results would provide data for the analysis of Ci acquisition and transport mechanism in S.japonica gametophytes.