Department of Earth Sciences, ETH Zurich, Sonnegstrasse 5, Zurich, 8092, Switzerland.
State Key Laboratory of Marine Geology, Tongji University, Shanghai, China.
J Phycol. 2020 Oct;56(5):1283-1294. doi: 10.1111/jpy.13017. Epub 2020 Jun 15.
Membrane permeabilities to CO and HCO constrain the function of CO concentrating mechanisms that algae use to supply inorganic carbon for photosynthesis. In diatoms and green algae, plasma membranes are moderately to highly permeable to CO but effectively impermeable to HCO . Here, CO and HCO membrane permeabilities were measured using an O-exchange technique on two species of haptophyte algae, Emiliania huxleyi and Calcidiscus leptoporus, which showed that the plasma membranes of these species are also highly permeable to CO (0.006-0.02 cm · s ) but minimally permeable to HCO . Increased temperature and CO generally increased CO membrane permeabilities in both species, possibly due to changes in lipid composition or CO channel proteins. Changes in CO membrane permeabilities showed no association with the density of calcium carbonate coccoliths surrounding the cell, which could potentially impede passage of compounds. Haptophyte plasma-membrane permeabilities to CO were somewhat lower than those of diatoms but generally higher than membrane permeabilities of green algae. One caveat of these measurements is that the model used to interpret O-exchange data assumes that carbonic anhydrase, which catalyzes O-exchange, is homogeneously distributed in the cell. The implications of this assumption were tested using a two-compartment model with an inhomogeneous distribution of carbonic anhydrase to simulate O-exchange data and then inferring plasma-membrane CO permeabilities from the simulated data. This analysis showed that the inferred plasma-membrane CO permeabilities are minimal estimates but should be quite accurate under most conditions.
CO 和 HCO 的膜通透性限制了藻类用于为光合作用提供无机碳的 CO 浓缩机制的功能。在硅藻和绿藻中，质膜对 CO 的通透性适中至高，但对 HCO 有效不可渗透。在这里，使用 O 交换技术测量了两种甲藻，Emiliania huxleyi 和 Calcidiscus leptoporus 的 CO 和 HCO 膜通透性，结果表明这些物种的质膜对 CO 也具有高通透性（0.006-0.02 cm·s），但对 HCO 最小通透性。温度和 CO 的升高通常会增加这两个物种的 CO 膜通透性，这可能是由于脂质组成或 CO 通道蛋白的变化所致。CO 膜通透性的变化与围绕细胞的碳酸钙颗石的密度没有关联，这可能会阻碍化合物的通过。甲藻质膜对 CO 的通透性略低于硅藻，但通常高于绿藻的膜通透性。这些测量存在一个注意事项，即用于解释 O 交换数据的模型假设，催化 O 交换的碳酸酐酶均匀分布在细胞中。通过使用具有碳酸酐酶不均匀分布的两室模型来模拟 O 交换数据，然后从模拟数据中推断质膜 CO 通透性，从而检验了这一假设。该分析表明，推断出的质膜 CO 通透性是最小估计值，但在大多数情况下应该非常准确。
