Brechignac F, Andre M
Institut de Recherche Fondamentale, C.E.N. Cadarache, BP No. 1, 13115 Saint Paul Lez Durance, France.
Plant Physiol. 1985 Jul;78(3):551-4. doi: 10.1104/pp.78.3.551.
An experimental system consisting of a gas exchange column linked to an assimilation chamber has been developed to record continuously the free dissolved CO(2) concentration in seawater containing marine plants. From experiments performed on the red macroalga Chondrus crispus (Rhodophyta, Gigartinales), this measurement is in agreement with the free CO(2) concentration calculated from the resistance to CO(2) exchanges in a biphasic system (gas and liquid) as earlier reported. The response time of this apparatus is short enough to detect, in conditions of constant pH, a photosynthesis-caused gradient between free CO(2) and HCO(3) (-) pools which half-equilibrates in 25 seconds. Abolished by carbonic anhydrase, the magnitude of this gradient increases with decreasing time of seawater transit from the chamber to the column apparatus. But its maximum magnitude (0.35 micromolar CO(2)) is negligible compared to the difference between air and free CO(2) (11.4 micromolar CO(2)). This illustrates the extent of the physical limiting-step occurring at the air-water interface when inorganic carbon consumption in seawater is balanced by dissolving gaseous CO(2). The direction of this small free CO(2)/HCO(3) (-) gradient indicates that HCO(3) (-) is consumed during photosynthesis.
已开发出一种实验系统，该系统由连接到同化室的气体交换柱组成，用于连续记录含有海洋植物的海水中游离溶解的二氧化碳浓度。通过对红色大型海藻角叉菜（红藻门，杉藻目）进行的实验，该测量结果与先前报道的根据双相系统（气体和液体）中二氧化碳交换阻力计算出的游离二氧化碳浓度一致。该仪器的响应时间足够短，能够在恒定pH条件下检测到光合作用导致的游离二氧化碳和碳酸氢根（HCO₃⁻）库之间的梯度，该梯度在25秒内达到半平衡。该梯度的大小会因碳酸酐酶而消除，且随着海水从同化室到柱形仪器的传输时间减少而增加。但其最大幅度（0.35微摩尔二氧化碳）与空气和游离二氧化碳之间的差值（11.4微摩尔二氧化碳）相比可忽略不计。这说明了当海水中无机碳的消耗通过溶解气态二氧化碳来平衡时，在气 - 水界面发生的物理限制步骤的程度。这个小的游离二氧化碳/碳酸氢根（HCO₃⁻）梯度的方向表明，碳酸氢根（HCO₃⁻）在光合作用过程中被消耗。
