Photosynthetic inorganic carbon utilization of gametophytes and sporophytes of Undaria pinnatifida (Phaeophyceae)

Abstract

X. Zhang, H. Hu and T. Tan. 2006. Photosynthetic inorganic carbon utilization of gametophytes and sporophytes of Undaria pinnatifida (Phaeophyceae). Phycologia 45: 642–647. DOI: 10.2216/05-28.1

The characteristics of inorganic carbon assimilation by photosynthesis were investigated in male and female gametophytes and juvenile sporophytes of Undaria pinnatifida. Gametophytes and sporophytes have detectable extracellular and intracellular carbonic anhydrase (CA) activity, and the CA inhibitor, acetazolamide (AZ), significantly inhibited their photosynthesis O₂ evolution. In pH-drift experiments, it was found that gametophytes did not raise the final pH of seawater above 9.00 (CO₂ concentrations of about 2.2 μM), indicating a low ability to utilize inorganic carbon. In contrast, sporophytes rapidly raised pH to over 9.53 and depleted the free CO₂ concentration to less than 0.16 μM. The apparent photosynthetic affinity for CO₂ was almost the same for gametophytes and sporophytes, whereas gametophytes had a much lower affinity for HCO₃⁻ than sporophytes. Two inhibitors of band 3 anion exchange protein (DIDS and SITS) inhibited the photosynthesis of gametophytes but not that of sporophytes. It was indicated that both gametophytes and sporophytes were capable of using HCO₃⁻, which involved the external CA activity, and a direct HCO₃⁻ use also occurred in the former, but the latter showed a greater capacity of HCO₃⁻ use than the former. In addition, male and female gametophytes did not show great differences in the inorganic carbon uptake mechanism underlying photosynthesis.

Key Words::

• Carbonic anhydrase
• Gametophytes
• Inorganic carbon
• Photosynthesis
• Sporophytes
• Undaria pinnatifida

ACKNOWLEDGMENTS

This study was supported by the Key Laboratory of Bioprocess of Beijing, P.R. China (SYS100100421).