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Published on April 21, 2006; 10.1104/pp.106.079616

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Received February 23, 2006
Returned for revision March 9, 2006
Accepted April 2, 2006

Evidence for K+-dependent HCO3- utilization in the marine diatom Phaeodactylum tricornutum

X. W. Chen *, C. E. Qiu , and J. Z. Shao

Department of Biology and Hubei Key Laboratory of Bioanalytical Technique, Hubei Normal University, Huangshi 435002, Hubei, China

* Corresponding author; email: xiongwenchen{at}eyou.com.

Photosynthetic utilization of inorganic carbon in the marine diatom Phaeodactylum tricornutum was investigated by the pH drift experiment, the measurement of K1/2 values of DIC with pH change and the comparison of rate of photosynthesis with rate of the theoretical CO2 formation from uncatalyzed HCO3- conversion in the medium. The higher pH compensation point (10.3) and insensitivity of photosynthetic rate to Acetazolamide (AZ) indicated that the alga has good capacity for direct HCO3- utilization. The photosynthetic rate reached 150 times the theoretical CO2 supply rate at 100 µmolL-1 DIC (pH9.0) in the presence of 10 mmolL-1 K+ and 46 times that in the absence of K+, indicating that for pH 9.4-grown P. tricornutum HCO3- in the medium is take up through K+-dependent and -independent HCO3- transports. The K1/2 (CO2) values at pH8.2 were about 4 times higher than those at pH 9.0 and whereas the K1/2 (HCO3-) values at pH 8.2 were slightly lower than those at pH 9.0 whether without or with K+, providing farther evidence for the presence of the two HCO3- transport patterns in this alga. Photosynthetic rate and affinity for HCO3- in the presence of K+, respectively, were about 2-fold and 7-fold higher than those in the absence of K+, indicating that K+-dependent HCO3- transport is a predominant pattern of HCO3- cellular uptake in low DIC concentration. However, as P. tricornutum was cultured at pH 7.2 or 8.0, photosynthetic affinities to HCO3- were not affected by K+, implying that K+-dependent HCO3- transport is induced when P. tricornutum was cultured at high alkaline pH.






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