Organisms that are adapted to extreme environments, and extremophiles

Extremophiles live in environments no other organisms can. Perhaps the most extreme environmental conditions can be found in hydrothermal vents, hot springs, the deep sea, in deserts, the pole areas and at high-altitude mountains. Extreme changes in temperature and irradiation and long periods of snow cover are characteristic of the two latter habitats. The microscopic "snow algae", which can give a red or green hue to snow fields and glaciers, are examples for organisms that live in alpine and polar regions.

"Desiccation tolerant" organisms are extreme life-forms too, although they do not necessarily live in extreme environments. They are able to withstand desiccation, that is, their water content can equilibrate with ambient relative humidity. In some cases (for example, over silica gel under laboratory conditions), this can be as dry as 3% water content. In the desiccated state, these organisms can survive long periods of time. When water becomes available again, they "spring back to life" and resume metabolism. Lichens are typical examples of desiccation tolerant organisms, and they make up to an estimated 80% of the vegetation cover in alpine and polar regions. Many bryophytes and a few ferns, but only relatively few higher plants, the so-called resurrection angiosperms, are also desiccation tolerant. However, most pollen and seeds of higher plants (termed "orthodox") are desiccation tolerant, and their ability to survive in the dry state is a prerequisite for their famous longevity over decades and even centuries.

Extreme life-forms are subject to extreme changes in their environment, and hence, they are fascinating objects to study stress response. We are interested to enhance our understanding of the biochemical mechanisms of stress response, adaptation and acclimation in plants that have adapted to extreme environments, with a special interest in seeds, lichens and resurrection plants.

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