Arata Paula X, Alberghina Josefina, Confalonieri Viviana, Errea María I, Estevez José M, Ciancia Marina
Universidad de Buenos Aires, Facultad de Agronomía, Departamento de Biología Aplicada y Alimentos, Cátedra de Química de Biomoléculas, Buenos Aires, Argentina.
Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Ecología, Genética y Evolución, Instituto IEGEBA (UBA-CONICET), Buenos Aires, Argentina.
Front Plant Sci. 2017 Nov 13;8:1927. doi: 10.3389/fpls.2017.01927. eCollection 2017.
The presence of sulfated polysaccharides in of seaweeds is considered to be a consequence of the physiological adaptation to the high salinity of the marine environment. Recently, it was found that sulfated polysaccharides were present in certain freshwater species and some vascular plants. (Ulvophyceae, Chlorophyta) is one of the largest genera of green algae that are able to grow in both, seas and freshwater courses. Previous studies carried out on the water-soluble polysaccharides of the marine species established the presence of sulfated xylogalactoarabinans constituted by a backbone of 4-linked β-L-arabinopyranose units partially sulfated mainly on C3 and also on C2 with partial glycosylation, mostly on C2, with terminal β-D-xylopyranose or β-D-galactofuranose units. Besides, minor amounts of 3-, 6- and/or 3,6-linked β-D-galactan structures, with galactose in the pyranosic form were detected. In this work, the main water soluble cell wall polysaccharides from the freshwater alga were characterized. It was found that this green alga biosynthesizes sulfated polysaccharides, with a structure similar to those found in marine species of this genus. Calibration of molecular clock with fossil data suggests that colonization of freshwater environments occurred during the Miocene by its ancestor. Therefore, the presence of sulfated polysaccharides in the freshwater green macroalga could be, in this case, an adaptation to transient desiccation and changes in ionic strength. Retention of sulfated polysaccharides at the cell walls may represent a snapshot of an evolutionary event, and, thus constitutes an excellent model for further studies on the mechanisms of sulfation on cell wall polysaccharides and environmental stress co-evolution.
海藻中硫酸化多糖的存在被认为是对海洋环境高盐度生理适应的结果。最近，人们发现某些淡水藻类物种和一些维管植物中也存在硫酸化多糖。石莼属（绿藻纲，绿藻门）是能够在海洋和淡水环境中生长的最大绿藻属之一。先前对该属海洋物种水溶性多糖的研究确定了硫酸化木糖半乳阿拉伯聚糖的存在，其由部分主要在C3以及C2上硫酸化且带有部分糖基化（大多在C2上）的1,4-连接的β-L-阿拉伯吡喃糖单元主链构成，带有末端β-D-木吡喃糖或β-D-呋喃半乳糖单元。此外，还检测到少量具有吡喃糖形式半乳糖的1,3-、1,6-和/或1,3,6-连接的β-D-半乳聚糖结构。在这项工作中，对淡水藻类石莼的主要水溶性细胞壁多糖进行了表征。发现这种绿藻生物合成硫酸化多糖，其结构与该属海洋物种中发现的结构相似。用化石数据校准分子钟表明，其祖先在中新世期间发生了淡水环境定殖。因此，在这种情况下，淡水绿大型海藻中硫酸化多糖的存在可能是对短暂干燥和离子强度变化的一种适应。硫酸化多糖在细胞壁上的保留可能代表了一个进化事件的快照，因此构成了进一步研究细胞壁多糖硫酸化机制和环境应激共同进化的优秀模型。
