title: Evidence for K+-dependent HCO3- utilization in the marine diatom Phaeodactylum tricornutum.
abstract: Photosynthetic utilization of inorganic carbon in the marine diatom Phaeodactylum tricornutum was investigated by the pH drift experiment, measurement of K(1/2) values of dissolved inorganic carbon (DIC) with pH change, and comparison of the rate of photosynthesis with the rate of the theoretical CO(2) formation from uncatalyzed HCO(3)(-) conversion in the medium. The higher pH compensation point (10.3) and insensitivity of the photosynthetic rate to acetazolamide indicate that the alga has good capacity for direct HCO(3)(-) utilization. The photosynthetic rate reached 150 times the theoretical CO(2) supply rate at 100 micromol L(-1) DIC (pH 9.0) in the presence of 10 mmol L(-1) K(+) and 46 times that in the absence of K(+), indicating that for pH 9.4-grown P. tricornutum, HCO(3)(-) in the medium is taken up through K(+)-dependent and -independent HCO(3)(-) transporters. The K(1/2) (CO(2)) values at pH 8.2 were about 4 times higher than those at pH 9.0, whereas the K(1/2) (HCO(3)(-)) values at pH 8.2 were slightly lower than those at pH 9.0 whether without or with K(+), providing further evidence for the presence of the two HCO(3)(-) transport patterns in this alga. Photosynthetic rate and affinity for HCO(3)(-) in the presence of K(+), respectively, were about 2- and 7-fold higher than those in the absence of K(+), indicating that K(+)-dependent HCO(3)(-) transport is a predominant pattern of HCO(3)(-) cellular uptake in low DIC concentration. However, as P. tricornutum was cultured at pH 7.2 or 8.0, photosynthetic affinities to HCO(3)(-) were not affected by K(+), implying that K(+)-dependent HCO(3)(-) transport is induced when P. tricornutum is cultured at high alkaline pH.
authors.affiliation: Department of Biology and Hubei Key Laboratory of Bioanalytical Technique, Hubei Normal University, Huangshi 435002, Hubei, China. xiongwenchen@eyou.com
authors.forename: Xiongwen
authors.initials: X
authors.lastname: Chen
authors.forename: C E
authors.initials: CE
authors.lastname: Qiu
authors.forename: J Z
authors.initials: JZ
authors.lastname: Shao
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D017377:Diatoms / Q000378:metabolism* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D010788:Photosynthesis; D011188:Potassium / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D011188:Potassium