Data from: Measuring CO2 and HCO3- permeabilities of isolated chloroplasts using a MIMS-18O approach

To support photosynthetic CO2 fixation by Rubisco, the chloroplast must be fed with inorganic carbon in the form of CO2 or bicarbonate. However, the mechanisms allowing the rapid passage of this gas and this charged molecule through the bounding membranes of the chloroplast envelope are not yet completely elucidated. We describe here a method allowing us to measure the permeability of these two molecules through the chloroplast envelope using a membrane inlet mass spectrometer and 18O-labelled inorganic carbon. We established that the internal stromal carbonic anhydrase activity is not limiting for this technique, and precisely measured the chloroplast surface area and permeability values for CO2 and bicarbonate. This was performed on chloroplasts from several plant species, with values ranging from 2.3 × 10–4 m s–1 to 8 × 10–4 m s–1 permeability for CO2 and 1 × 10–8 m s–1 for bicarbonate. We were able to apply our method to chloroplasts from an Arabidopsis aquaporin mutant, and this showed that CO2 permeability was reduced 50% in the mutant compared with the wild-type reference.为支持核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）介导的光合CO₂固定过程，叶绿体需要以CO₂或碳酸氢盐（bicarbonate）形式获取无机碳源。然而，介导该气体与带电分子快速跨叶绿体被膜（chloroplast envelope）界膜转运的机制尚未完全阐明。本文报道一种实验方法，可借助膜进样质谱仪（membrane inlet mass spectrometer）与氧-18（¹⁸O）标记的无机碳底物，精准测定这两种分子跨叶绿体被膜的通透系数。本研究证实叶绿体基质内的碳酸酐酶活性不会对该实验方法造成限制，并精确测得叶绿体表面积以及CO₂与碳酸氢盐的跨膜通透系数。该实验以多种植物的叶绿体为材料，测得CO₂的通透系数范围为2.3×10⁻⁴ m·s⁻¹至8×10⁻⁴ m·s⁻¹，碳酸氢盐的通透系数则为1×10⁻⁸ m·s⁻¹。我们将该方法应用于拟南芥（Arabidopsis）水通道蛋白（aquaporin）突变体的叶绿体实验，结果显示相较于野生型对照，突变体的CO₂通透系数较野生型降低了50%。