Chen Xiongwen, Qiu C E, Shao J Z
Department of Biology and Hubei Key Laboratory of Bioanalytical Technique, Hubei Normal University, Huangshi 435002, Hubei, China.
Plant Physiol. 2006 Jun;141(2):731-6. doi: 10.1104/pp.106.079616. Epub 2006 Apr 21.
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.
通过pH漂移实验、测量溶解无机碳（DIC）随pH变化的K(1/2)值以及比较光合作用速率与培养基中未催化的HCO(3)(-)转化产生理论CO(2)的速率，研究了海洋硅藻三角褐指藻对无机碳的光合利用。较高的pH补偿点（10.3）以及光合速率对乙酰唑胺不敏感表明该藻类具有良好的直接利用HCO(3)(-)的能力。在10 mmol L(-1) K(+)存在的情况下，当DIC浓度为100 micromol L(-1)（pH 9.0）时，光合速率达到理论CO(2)供应速率的150倍，而在无K(+)时为46倍，这表明对于在pH 9.4条件下生长的三角褐指藻，培养基中的HCO(3)(-)通过依赖K(+)和不依赖K(+)的HCO(3)(-)转运体被吸收。pH 8.2时的K(1/2)（CO(2)）值比pH 9.0时高约4倍，而无论有无K(+)，pH 8.2时的K(1/2)（HCO(3)(-)）值均略低于pH 9.0时的值，这为该藻类中存在两种HCO(3)(-)转运模式提供了进一步证据。有K(+)存在时的光合速率和对HCO(3)(-)的亲和力分别比无K(+)时高约2倍和7倍，表明在低DIC浓度下，依赖K(+)的HCO(3)(-)转运是细胞吸收HCO(3)(-)的主要模式。然而，当三角褐指藻在pH 7.2或8.0条件下培养时，其对HCO(3)(-)的光合亲和力不受K(+)影响，这意味着当三角褐指藻在高碱性pH条件下培养时会诱导依赖K(+)的HCO(3)(-)转运。
