Still sprouting after 32,000 years

Published in The Hindu on February 21, 2012

For the first time ever, scientists have been able to grow ancient flowering plants (Silene stenophylla ) from immature fruit tissues buried 38 metres under the North-eastern Siberian ice deposits about 32,000 years ago. The tissues were recovered from the burrow of a ground squirrel.

The regenerated plants flowered and also produced seeds. These seeds were in turn able to grow into plants that were identical to the parent plants.  If immature tissues and organs are known to be more regenerative than mature ones, this study published today (February 21) in the Proceedings of the National Academy of Sciences journal has proved it conclusively. They used tissue culture and micropropagation to make the immature placental tissue grow into healthy and sexually reproducing plants.

Gamma rays

Another significant finding is that tissues remained viable and seeds germinated despite accumulating total gamma ray radiation of 0.07 kGy during the long period of burial.

Interestingly, S. stenophylla (perennial herbaceous plant from the family Caryophyllaceae) has not gone extinct. “At present, plants of S. stenophylla are the most ancient, viable, multicellular, living organisms,” the authors noted. Hence scientists from the Russian Academy of Sciences, Pushchino, Russia, were able to grow the ancient plants and compare them with those found in the same region.

The ancient plants and those still in existence (extant) were morphologically identical till the flowering stage.  Differences cropped up only when the plants started flowering. The petals of the plants found today were wider and dissected, and all the flowers were bisexual.  However, the petals of the ancient plants were narrower, and the primary flowers were strictly female, followed by bisexual flowers that formed later. The study helped understand the rate of microevolution in the plants.

The seeds and fruits were preserved at about -7°C and remained undisturbed in the burrow for the entire period of burial.  No permafrost degradation in the form of ice melting has been recorded. It has long been known that seed viability increases as the storage temperate and moisture content decrease. Siberian permafrost offered both these conditions. This proves that ancient immature fruit tissues are capable of growing into plants if the preservation conditions are right.

Permafrost sediments, the authors say, might represent a rich source of wild plant species and ancient gene pools, long believed to have gone extinct: “This natural cryopreservation of plant tissues over thousands of years demonstrates a role for permafrost as a depository for an ancient gene pool … a laboratory for the study of rates of microevolution.”

The fact that burrows are constructed by animals against frozen ice and ice complexes are formed immediately on sedimentation makes them ideal locations for safe storage.

About 70 fossil burrows have been found in the region, of which more than 30 have been investigated. The burrows contain invaluable supply of plant seeds and fruits. “The number of seeds and fruits reaches up to 600,000 to 800,000 in some chambers,” they wrote.

Squirrel burrows with seeds deposited around the same time have been identified in Alaska and Yukon as well. “This indicates that the whole of Beringia has a great potential as storage of ancient life preserved in permafrost,” the authors underlined.