Procházková Lenka, Remias Daniel, Bilger Wolfgang, Křížková Heda, Řezanka Tomáš, Nedbalová Linda
Faculty of Science, Charles University, Prague, Czechia.
School of Engineering, University of Applied Sciences Upper Austria, Wels, Austria.
Front Plant Sci. 2020 Dec 17;11:617250. doi: 10.3389/fpls.2020.617250. eCollection 2020.
Melting mountainous snowfields are populated by extremophilic microorganisms. An alga causing orange snow above timberline in the High Tatra Mountains (Poland) was characterised using multiple methods examining its ultrastructure, genetics, life cycle, photosynthesis and ecophysiology. Based on light and electron microscopy and ITS2 rDNA, the species was identified as (Chlorophyceae). Recently, the taxon was described from Japan. However, cellular adaptations to its harsh environment and details about the life cycle were so far unknown. In this study, the snow surface population consisted of egg-shaped cysts containing large numbers of lipid bodies filled presumably with the secondary carotenoid astaxanthin. The outer, spiked cell wall was shed during cell maturation. Before this developmental step, the cysts resembled a different snow alga, . The remaining, long-lasting smooth cell wall showed a striking UV-induced blue autofluorescence, indicating the presence of short wavelengths absorbing, protective compounds, potentially sporopollenin containing polyphenolic components. Applying a chlorophyll fluorescence assay on intact cells, a significant UV-A and UV-B screening capability of about 30 and 50%, respectively, was measured. Moreover, intracellular secondary carotenoids were responsible for a reduction of blue-green light absorbed by chloroplasts by about 50%. These results revealed the high capacity of cysts to reduce the impact of harmful UV and high visible irradiation to the chloroplast and nucleus when exposed at alpine snow surfaces during melting. Consistently, the observed photosynthetic performance of photosystem II (evaluated by fluorometry) showed no decline up to 2100 μmol photons m s. Cysts accumulated high contents of polyunsaturated fatty acids (about 60% of fatty acids), which are advantageous at low temperatures. In the course of this study, was found also in Slovakia, Italy, Greece and the United States, indicating a widespread distribution in the Northern Hemisphere.
融化的山区雪地里生活着嗜极微生物。对一种导致波兰高塔特拉山树木线以上出现橙色雪的藻类进行了多种方法的表征，研究了其超微结构、遗传学、生命周期、光合作用和生态生理学。基于光学显微镜和电子显微镜以及ITS2核糖体DNA，该物种被鉴定为（绿藻纲）。最近，该分类单元在日本也有描述。然而，到目前为止，其细胞对恶劣环境的适应以及生命周期的细节尚不清楚。在本研究中，雪表面群体由卵形囊肿组成，囊肿内含有大量脂质体，推测其中填充有次生类胡萝卜素虾青素。在细胞成熟过程中，外部带刺的细胞壁会脱落。在这一发育步骤之前，囊肿类似于另一种不同的雪藻。剩下的、持久的光滑细胞壁显示出强烈的紫外线诱导蓝色自发荧光，表明存在吸收短波长的保护性化合物，可能含有多酚成分的孢粉素。对完整细胞进行叶绿素荧光测定，分别测量到约30%和50%的显著紫外线-A和紫外线-B筛选能力。此外，细胞内次生类胡萝卜素使叶绿体吸收的蓝绿光减少了约50%。这些结果表明，囊肿在融化过程中暴露于高山雪表面时，具有很高的能力来减少有害紫外线和高可见光对叶绿体和细胞核的影响。一致地，观察到的光系统II的光合性能（通过荧光测定法评估）在高达2100 μmol光子·m²·s⁻¹时没有下降。囊肿积累了高含量的多不饱和脂肪酸（约占脂肪酸的60%），这在低温下是有利的。在这项研究过程中，还在斯洛伐克、意大利、希腊和美国发现了该藻类，表明其在北半球广泛分布。
