Espie G S, Kandasamy R A
Department of Botany, Erindale College, University of Toronto, Mississauga, Ontario, Canada L5L 1C6.
Plant Physiol. 1992 Feb;98(2):560-8. doi: 10.1104/pp.98.2.560.
The active transport and intracellular accumulation of HCO(3) (-) by air-grown cells of the cyanobacterium Synechococcus UTEX 625 (PCC 6301) was strongly promoted by 25 millimolar Na(+).Na(+)-dependent HCO(3) (-) accumulation also resulted in a characteristic enhancement in the rate of photosynthetic O(2) evolution and CO(2) fixation. However, when Synechococcus was grown in standing culture, high rates of HCO(3) (-) transport and photosynthesis were observed in the absence of added Na(+). The internal HCO(3) (-) pool reached levels up to 50 millimolar, and an accumulation ratio as high as 970 was observed. Sodium enhanced HCO(3) (-) transport and accumulation in standing culture cells by about 25 to 30% compared with the five- to eightfold enhancement observed with air-grown cells. The ability of standing culture cells to utilize HCO(3) (-) from the medium in the absence of Na(+) was lost within 16 hours after transfer to air-grown culture and was reacquired during subsequent growth in standing culture. Studies using a mass spectrometer indicated that standing culture cells were also capable of active CO(2) transport involving a high-affinity transport system which was reversibly inhibited by H(2)S, as in the case for air-grown cells. The data are interpreted to indicate that Synechococcus possesses a constitutive CO(2) transport system, whereas Na(+)-dependent and Na(+)-independent HCO(3) (-) transport are inducible, depending upon the conditions of growth. Intracellular accumulation of HCO(3) (-) was always accompanied by a quenching of chlorophyll a fluorescence which was independent of CO(2) fixation. The extent of fluorescence quenching was highly dependent upon the size of the internal pool of HCO(3) (-) + CO(2). The pattern of fluorescence quenching observed in response to added HCO(3) (-) and Na(+) in air-grown and standing culture cells was highly characteristic for Na(+)-dependent and Na(+)-independent HCO(3) (-) accumulation. It was concluded that measurements of fluorescence quenching provide an indirect means for following HCO(3) (-) transport and the dynamics of intracellular HCO(3) (-) accumulation and dissipation.
25毫摩尔的Na⁺可强烈促进蓝藻聚球藻UTEX 625（PCC 6301）气生细胞对HCO₃⁻的主动运输和细胞内积累。Na⁺依赖的HCO₃⁻积累还导致光合O₂释放速率和CO₂固定速率显著提高。然而，当聚球藻在静置培养中生长时，在不添加Na⁺的情况下也观察到了较高的HCO₃⁻运输速率和光合作用速率。细胞内HCO₃⁻库达到高达50毫摩尔的水平，并且观察到积累比高达970。与气生细胞中观察到的增强五到八倍相比，Na⁺使静置培养细胞中的HCO₃⁻运输和积累增强了约25%至30%。静置培养细胞在不添加Na⁺的情况下利用培养基中HCO₃⁻的能力在转移到气生培养16小时后丧失，并在随后的静置培养生长过程中重新获得。使用质谱仪的研究表明，静置培养细胞也能够进行主动CO₂运输，涉及一个高亲和力运输系统，该系统像气生细胞一样被H₂S可逆抑制。数据解释表明聚球藻拥有一个组成型CO₂运输系统，而Na⁺依赖和Na⁺非依赖的HCO₃⁻运输是可诱导的，这取决于生长条件。HCO₃⁻的细胞内积累总是伴随着叶绿素a荧光的猝灭这一过程独立于CO₂固定。荧光猝灭的程度高度依赖于HCO₃⁻ + CO₂细胞内库的大小。在气生和静置培养细胞中，响应添加的HCO₃⁻和Na⁺观察到的荧光猝灭模式对于Na⁺依赖和Na⁺非依赖的HCO₃⁻积累具有高度特征性。得出的结论是，荧光猝灭测量为追踪HCO₃⁻运输以及细胞内HCO₃⁻积累和消散的动态提供了一种间接手段。
