2Author for correspondence: e-mail email@example.com.
PHOTOSYNTHETIC UTILIZATION OF INORGANIC CARBON IN THE ECONOMIC BROWN ALGA, HIZIKIA FUSIFORME (SARGASSACEAE) FROM THE SOUTH CHINA SEA1
Article first published online: 24 NOV 2003
Journal of Phycology
Volume 39, Issue 6, pages 1095–1100, December 2003
How to Cite
Zou, D., Gao, K. and Xia, J. (2003), PHOTOSYNTHETIC UTILIZATION OF INORGANIC CARBON IN THE ECONOMIC BROWN ALGA, HIZIKIA FUSIFORME (SARGASSACEAE) FROM THE SOUTH CHINA SEA. Journal of Phycology, 39: 1095–1100. doi: 10.1111/j.0022-3646.2003.03-038.x
1Received 13 February 2003. Accepted 5 August 2003.
- Issue published online: 24 NOV 2003
- Article first published online: 24 NOV 2003
- brown alga;
- carbonic anhydrase;
- inorganic carbon;
- Hizikia fusiforme;
- marine macroalgae;
The mechanism of inorganic carbon (Ci) acquisition by the economic brown macroalga, Hizikia fusiforme (Harv.) Okamura (Sargassaceae), was investigated to characterize its photosynthetic physiology. Both intracellular and extracellular carbonic anhydrase (CA) were detected, with the external CA activity accounting for about 5% of the total. Hizikia fusiforme showed higher rates of photosynthetic oxygen evolution at alkaline pH than those theoretically derived from the rates of uncatalyzed CO2 production from bicarbonate and exhibited a high pH compensation point (pH 9.66). The external CA inhibitor, acetazolamide, significantly depressed the photosynthetic oxygen evolution, whereas the anion-exchanger inhibitor 4,4′-diisothiocyano-stilbene-2,2′-disulfonate had no inhibitory effect on it, implying the alga was capable of using HCO3− as a source of Ci for its photosynthesis via the mediation of the external CA. CO2 concentrations in the culture media affected its photosynthetic properties. A high level of CO2 (10,000 ppmv) resulted in a decrease in the external CA activity; however, a low CO2 level (20 ppmv) led to no changes in the external CA activity but raised the intracellular CA activity. Parallel to the reduction in the external CA activity at the high CO2 was a reduction in the photosynthetic CO2 affinity. Decreased activity of the external CA in the high CO2 grown samples led to reduced sensitiveness of photosynthesis to the addition of acetazolamide at alkaline pH. It was clearly indicated that H. fusiforme, which showed CO2-limited photosynthesis with the half-saturating concentration of Ci exceeding that of seawater, did not operate active HCO3− uptake but used it via the extracellular CA for its photosynthetic carbon fixation.