Characeae are closely related to the ancient algal ancestors of all land plants. The long characean cells display a pH banding pattern to facilitate inorganic carbon import in the acid zones for photosynthetic efficiency. The excess OH⁻, generated in the cytoplasm after CO₂ is taken into the chloroplasts, is disposed of in the alkaline band. To identify the transporter responsible, we searched the Chara australis transcriptome for homologues of mouse Slc4a11, which functions as OH⁻/H⁺ transporter. We found a single Slc4-like sequence CL5060.2 (named CaSLOT). When CaSLOT was expressed in Xenopus oocytes, an increase in membrane conductance and hyperpolarization of resting potential difference (PD) was observed with external pH increase to 9.5. These features recall the behavior of Slc4a11 in oocytes and are consistent with the action of a pH-dependent OH⁻/H⁺ conductance. The large scatter in the data might reflect intrinsic variability of CaSLOT transporter activation, inefficient expression in the oocyte due to evolutionary distance between ancient algae and frogs, or absence of putative activating factor present in Chara cytoplasm. CaSLOT homologues were found in chlorophyte and charophyte algae, but surprisingly not in related charophytes Zygnematophyceae or Coleochaetophyceae.

Characeae 与所有陆地植物的古老藻类祖先密切相关。长的characean 细胞显示出一种pH 条带模式，以促进酸性区域中的无机碳输入，从而提高光合作用效率。_{在CO 2}进入叶绿体后在细胞质中产生的过量OH ^{-被处理在碱性带中。}为了确定负责的转运蛋白，我们在Chara australis转录组中搜索了小鼠 Slc4a11 的同源物，其功能为 OH ^- /H ⁺转运蛋白。我们发现了一个类似 Slc4 的序列 CL5060.2（命名为 CaSLOT）。当 CaSLOT 在非洲爪蟾中表达时卵母细胞，随着外部 pH 值增加到 9.5，膜电导增加和静息电位差 (PD) 超极化。这些特征让人想起卵母细胞中 Slc4a11 的行为，并且与 pH 依赖性 OH ^- /H ⁺电导的作用一致。数据中的大分散可能反映了 CaSLOT 转运蛋白激活的内在变异性，由于古代藻类和青蛙之间的进化距离，卵母细胞中的低效表达，或Chara细胞质中不存在推定的激活因子。在叶绿素和轮藻中发现了 CaSLOT 同源物，但令人惊讶的是，在相关的轮生植物 Zygnematophyceae 或 Coleochaetophyceae 中没有发现 CaSLOT 同源物。