Huertas I Emma, Colman Brian, Espie George S
Department of Biology, York University, 4700 Keele St, Toronto, Ontario M3J 1P3, Canada. Department of Botany, University of Toronto at Mississauga, 3359 Mississauga Rd, Mississauga, Ontario L5L 1C6, Canada. Current address: Instituto de Ciencias Marinas de Andalucia, Avenida Republica Saharaui s/n, 11510 Puerto Real, Cadiz, Spain.Corresponding author; email:
Department of Biology, York University, 4700 Keele St, Toronto, Ontario M3J 1P3, Canada.
Funct Plant Biol. 2002 Apr;29(3):271-277. doi: 10.1071/PP01181.
The eustigmatophyceans are primitive unicellular algae that represent the most basal group of ochrophytes. They are believed to be obligate photoautotrophs, occurring mainly in freshwater and soil but with some marine representatives. The freshwater eustigmatophytes Monodus subterraneus and Vischeria stellata, and the marine eustigmatophyte Nannochloropsis gaditana, have been studied by mass spectrometry with respect to their characteristics for inorganic carbon (Ci) uptake. A CO2 concentrating mechanism was found in all three, but an external carbonic anhydrase (CA) was not detected. The acquisition of Ci from the external medium was based on the active transport of HCO3, CO2, or both. In particular, N. gaditana was able to use HCO3 exclusively as an exogenous carbon source for photosynthesis, with this HCO3 being subsequently converted to CO2 by an intracellular CA for photosynthetic fixation. A unique characteristic of this species was its capacity to transport HCO3 during prolonged periods of time in the dark. In contrast, M. subterraneus utilized CO2 alone through an active transport process, whereas V. stellataexhibited the capacity to transport both HCO3 and CO2. The uptake of CO2 also continued in the dark in V. stellatacells. Regardless of the Ci species taken up, transport was abolished by anoxia and by inhibitors of mitochondrial respiration. These results indicate that that the supply of Ci for photosynthetic CO2 fixation is partly dependent upon mitochondrial activity in these primitive eukaryotes.
黄藻门藻类是原始的单细胞藻类，代表了褐藻植物中最基部的类群。它们被认为是专性光合自养生物，主要存在于淡水和土壤中，但也有一些海洋代表物种。淡水黄藻门藻类地下单鞭金藻（Monodus subterraneus）和星状维斯藻（Vischeria stellata）以及海洋黄藻门藻类加的斯等鞭金藻（Nannochloropsis gaditana），已通过质谱分析法对其无机碳（Ci）摄取特性进行了研究。在这三种藻类中均发现了二氧化碳浓缩机制，但未检测到外部碳酸酐酶（CA）。从外部介质获取Ci是基于HCO₃、CO₂或两者的主动运输。特别是，加的斯等鞭金藻能够仅将HCO₃用作光合作用的外源碳源，随后这种HCO₃会被细胞内的CA转化为CO₂用于光合固定。该物种的一个独特特征是其在黑暗中长时间运输HCO₃的能力。相比之下，地下单鞭金藻仅通过主动运输过程利用CO₂，而星状维斯藻表现出运输HCO₃和CO₂的能力。星状维斯藻细胞在黑暗中也持续摄取CO₂。无论摄取的Ci种类如何，缺氧和线粒体呼吸抑制剂都会消除运输。这些结果表明，在这些原始真核生物中，用于光合CO₂固定的Ci供应部分依赖于线粒体活性。
