Ochiai Teruhiko, Colman Brian, Matsuda Yusuke
Department of Bioscience, Kwansei-Gakuin University, 2-1 Gakuen, Sanda, Hyogo, 669-1337, Japan.
Plant Cell Environ. 2007 Aug;30(8):944-51. doi: 10.1111/j.1365-3040.2007.01684.x.
CO(2)-insensitive mutants of the green alga Chlorella ellipsoidea were previously shown to be unable to repress an inorganic carbon-concentrating mechanism (CCM) when grown under 5% CO(2). When air-grown, wild-type (WT) cells were transferred to 5% CO(2), an abrupt drop of P(max) to 43% the original level of air-grown cells was observed within the initial 12 h. Photosynthetic affinities of WT cells to dissolved inorganic carbon (DIC) were maintained at high levels for the initial 4 d of acclimation, and then decreased gradually to lower levels over the next 6 d. In contrast to WT cells, the CO(2)-insensitive mutant, ENU16, exhibited a constant P(max) at maximum levels and a low K(1/2)[DIC] throughout the acclimation period. The rapid P(max) drop within 12 h of acclimation in WT cells was significantly reduced by treatment with 0.5 mm of 6-ethoxybenzothiazole-2-sulphonamide (EZA), a specific membrane-permeable inhibitor of carbonic anhydrase (CA), suggesting the participation of internal CAs in the temporary drop in P(max) in WT cells. WT and ENU16 cells were grown in controlled equilibrium [CO(2)], and the photosynthetic rate of each acclimated cell type was measured under equilibrated growth [DIC] conditions. In WT cells acclimated to 0.14-0.4% [CO(2)], K(1/2)[DIC] values increased as [CO(2)] increased, and the photosynthetic rates at growth DIC conditions were shown to decrease to about 70% the P(max) level in this intermediate [CO(2)] range. Such decreases in the net photosynthetic rates were not observed in ENU16. These results suggest that algal primary production could be depressed significantly under moderately enriched CO(2) conditions as a result of acquiring intermediate affinities for DIC because of their sensitive responses to changes in the ambient [CO(2)].
先前的研究表明，椭圆小球藻的二氧化碳不敏感突变体在5%二氧化碳浓度下生长时，无法抑制无机碳浓缩机制（CCM）。当在空气中生长的野生型（WT）细胞转移到5%二氧化碳环境中时，在最初的12小时内，观察到P(max)突然下降至空气中生长细胞原始水平的43%。野生型细胞对溶解无机碳（DIC）的光合亲和力在适应的最初4天内保持在较高水平，然后在接下来的6天内逐渐下降至较低水平。与野生型细胞相反，二氧化碳不敏感突变体ENU16在整个适应期内表现出最大水平的恒定P(max)和较低的K(1/2)[DIC]。用0.5毫米的6-乙氧基苯并噻唑-2-磺酰胺（EZA）处理可显著降低野生型细胞在适应12小时内P(max)的快速下降，EZA是一种特定的可透过膜的碳酸酐酶（CA）抑制剂，这表明内部碳酸酐酶参与了野生型细胞中P(max)的暂时下降。野生型和ENU16细胞在受控的平衡[CO(2)]条件下生长，并在平衡生长[DIC]条件下测量每种适应细胞类型的光合速率。在适应于0.14 - 0.4%[CO(2)]的野生型细胞中，K(1/2)[DIC]值随着[CO(2)]的增加而增加，并且在该中间[CO(2)]范围内，生长DIC条件下的光合速率显示下降至P(max)水平的约70%。在ENU16中未观察到这种净光合速率的下降。这些结果表明，由于藻类对环境[CO(2)]变化的敏感反应，获得了对DIC的中等亲和力，藻类初级生产力在适度富集的CO(2)条件下可能会显著降低。
