Wednesday, June 12, 2013

Bryophytes: the recolonization of polar arctic regions after 400 years of ice entombment



Along the Canadian Arctic Archipelago glacier recession has been a common occurrence, but with this serious decrease in ice mass there emerges a silver lining. In the Sverdrup Pass, the Teardrop Glacier has retreated ~200 m from its boundary during the Little Ice Age (LIA) [1]. This glacier retreat has uncovered a species of subglacial flora that has been dormant for over 400 years. These organisms discovered under the ice are a population of bryophytes (an old group vascular plants including mosses, liverwarts, and hornwarts that do not exhibit a vascular system [2]). The remarkable regeneration of these organisms emphasizes their successful adaptation to extreme polar environments.

Previously to the discovery of these bryophytes, many scientists thought that these new areas exposed by melting glaciers were not viable due to their lengthy exposure to subarctic conditions. Mats of “dead” moss were observed and the popular belief that most populations from the LIA were deceased was reinforced. Contrary to this common understanding, organisms found in these glacier-recession areas show startling rates of regeneration and subsequent propagation from “dead moss mats” [1]. 
"Dead moss mat" found at the base of the Teardrop Glacier after being frozen for over 400 years [3].
photo linked from npr.org <http://www.npr.org/blogs/thetwo-way/2013/05/27/186518319/beneath-a-glaciers-white-researchers-see-green>
A quote from Catherine La Farge in a National Geographic article stated:

 "As we walked up to the edge of the glacier, we could see patches of mosses that seemed to be coming out from underneath the ice. They were blackened, but there were also tints of green in there as well. As I looked more closely I thought, 'Oh my gosh, what's this? Either this has somehow managed to retain a vestige of its original color or it's just started to grow again after centuries under the ice.' The thought of that just blew my mind" [4].

The bryophyte samples that were collected had already started to regrow by the time they were shipped to the laboratory for analysis. This was shocking news to the researchers since the vast majority of plants today cannot become viable after being frozen, but these special sub-glacier plants have the capacity to regrow themselves from very small pieces of plant matter. These organisms have the ability to clone themselves using totipotent cells that return from a differentiated to a dedifferentiated (meristematic) state.

This amazing ability is akin to reversion to stem cells in animals to create pluripotent cells. Another attribute of these bryophytes includes them being poikilohydric, which means the organism lacks the ability to control water content. The bryophyte cells can shut down physiologically during desiccation and revive when conditions are more favorable. This additional attribute means that these organisms can survive a very long time and like an endospore in bacteria, remain viable under extreme conditions. The reverted cell can then be re-purposed to propagate the organism once favorable conditions occur.


Growth of 400 year-old bryophyte samples treated only with water and light [5]
Photo linked from popsci.com <http://www.popsci.com/science/article/2013-05/400-year-old-mosses-regrown-lab>

Although being significant to understanding the evolution of glacial ecosystems, these bryophytes are technically not the oldest organisms to be regrown. A 31,800 year BP seed from Silene stenophylla was recovered from a Siberian permafrost and was recently cultured. In contrast to the bryophytes, the S. stenophylla  placental tissue was extracted from the seed, carefully cloned, and grown on specialized nutrient media to stimulate development [5]. The bryophytes were regrown merely by grinding gametophytic tissue (primarily stems and leaves) and sewing the material into potting soil or growth media followed by simple watering [1].

The ability of these organisms to regenerate is a very rich resource for learning more about how glacial regions evolved and provide a link in the evolutionary chain. The regenerative ability of the bryophytes is a unique mechanism that was lost among modern plants. The reintroduction of this genetic variation will impact transgenic organisms in research and has many implications for further study. Bryophytes are not the only organisms to be unveiled by the recession of massive glaciers, organisms that were additionally found include sub-glacial microbes such as cyanobacteria and eukaryotic microalgae.

The discovery of these sub-glacial organisms has been a eye-opener for researchers everywhere. Who could imagine that multiple organisms would be found entombed for 400+ years and still be able to regrow once favorable conditions were available. These organisms are amazing examples of how nature is an ever-evolving force that specializes in colonizing new environments uncovered by a changing planet. 

While the impact of melting glaciers is mostly negative, at least there is one positive aspect to global climate change. The information we can learn about these long-lost organisms will help biologists understand LIA ecosystems and their unique regenerative properties may be an important stepping stone in plant diversity. The techniques utilized by the bryophytes might also lead to breakthroughs in cellular regeneration and may provide a medical researchers a new approach to limb regeneration.



Works Cited:


Link to research paper
[1] http://www.pnas.org/content/110/24/9839

Reviews
[2] http://bryophytes.plant.siu.edu/bryojustified.html
[3] http://www.npr.org/blogs/thetwo-way/2013/05/27/186518319/beneath-a-glaciers-white-researchers-see-green
[4] http://news.nationalgeographic.com/news/2013/05/130528-frozen-moss-teardrop-glacier-environment-science/
[5] http://www.popsci.com/science/article/2013-05/400-year-old-mosses-regrown-lab

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