Stress resistance of polar hydro-terrestrial algae Zygnema spp. (Zygnematophyceae, Streptophyta)

Filamentous green microalgae of the genus Zygnema belong to the most common primary producers in the polar hydro-terrestrial environment. In such unstable habitats, organisms are subject to various stress factors, e.g., freeze-thaw cycles, desiccation and high irradiation levels. However, the stress resistance mechanisms that enable Zygnema spp. to thrive in this extreme environment are only partially understood. Therefore, polar Zygnema spp. were examined under various stress conditions using both field samples and cultures. Moreover, molecular phylogeny methods were applied that provided first insights into the diversity of polar Zygnema. Sequencing of the chloroplast gene rbcL revealed several different Zygnema genotypes and, surprisingly, one Zygnemopsis sp. with vegetative Zygnema sp. morphology. First set of experiments examined the effects of UV exposure. It turned out that polar strains of Zygnema produce phenolic substances as UV screens. These substances are most likely stored in vacuoles and other vesicles at the cell periphery, providing protection for other organelles. In the next study, Zygnema spp. were investigated under natural conditions in the Arctic. At the end of summer, the cells gradually lose their typical vegetative appearance (with large vacuoles and stellate chloroplasts)..