Svetlana Yashina
OLD DNA A plant has been generated from the fruit of
the narrow-leafed campion. It is the oldest plant by far to be grown
from ancient tissue.
This would be the oldest plant by far that has ever been grown from
ancient tissue. The present record is held by a date palm grown from a
seed some 2,000 years old that was recovered from the ancient fortress
of Masada in Israel.
Seeds and certain cells can last a long term under the right conditions,
but many claims of extreme longevity have failed on closer examination,
and biologists are likely to greet this claim, too, with reserve until
it can be independently confirmed. Tales of wheat grown from seeds in
the tombs of the pharaohs have long been discredited. Lupines were
germinated from seeds in a 10,000-year-old lemming burrow found by a
gold miner in the Yukon. But the seeds, later dated by the radiocarbon
method, turned out to be modern contaminants.
Despite this unpromising background, the new claim is supported by a
firm radiocarbon date. A similar avenue of inquiry into the deep past,
the field of ancient DNA, was at first discredited after claims of
retrieving dinosaur DNA proved erroneous, but with improved methods has
produced spectacular results like the reconstitution of the Neanderthal
genome.
The new report is by a team led by Svetlana Yashina and David
Gilichinsky of the Russian Academy of Sciences research center at
Pushchino, near Moscow, and appears in Tuesday’s issue of The
Proceedings of the National Academy of Sciences of the United States of
America.
“This is an amazing breakthrough,” said Grant Zazula of the Yukon
Paleontology Program at Whitehorse in Yukon Territory, Canada. “I have
no doubt in my mind that this is a legitimate claim.” It was Dr. Zazula
who showed that the apparently ancient lupine seeds found by the Yukon
gold miner were in fact modern.
But the Russians’ extraordinary report is likely to provoke calls for
more proof. “It’s beyond the bounds of what we’d expect,” said Alastair
Murdoch, an expert on seed viability at the University of Reading in
England. When poppy seeds are kept at minus 7 degrees Celsius, the
temperature the Russians reported for the campions, after only 160 years
just 2 percent of the seeds will be able to germinate, Dr. Murdoch
noted.
The Russian researchers excavated ancient squirrel burrows exposed on
the bank of the lower Kolyma River, an area thronged with mammoth and
woolly rhinoceroses during the last ice age. Soon after being dug, the
burrows were sealed with windblown earth, buried under 125 feet of
sediment and permanently frozen at minus 7 degrees Celsius.
Some of the storage chambers in the burrows contain more than 600,000
seeds and fruits. Many are from a species that most closely resembles a
plant found today, the narrow-leafed campion (Silene stenophylla).
Working with a burrow from the site called Duvanny Yar, the Russian
researchers tried to germinate the campion seeds, but failed. They then
took cells from the placenta, the organ in the fruit that produces the
seeds. They thawed out the cells and grew them in culture dishes into
whole plants.
Many plants can be propagated from a single adult cell, and this cloning
procedure worked with three of the placentas, the Russian researchers
report. They grew 36 ancient plants, which appeared identical to the
present day narrow-leafed campion until they flowered, when they
produced narrower and more splayed-out petals. Seeds from the ancient
plants germinated with 100 percent success, compared with 90 percent for
seeds from living campions.
The Russian team says it obtained a radiocarbon date of 31,800 years
from seeds attached to the same placenta from which the living plants
were propagated.
The researchers suggest that special circumstances may have contributed
to the remarkable longevity of the campion plant cells. Squirrels
construct their larders next to permafrost to keep seeds cool during the
arctic summers, so the fruits would have been chilled from the start.
The fruit’s placenta contains high levels of sucrose and phenols, which
are good antifreeze agents.
The Russians measured the ground radioactivity at the site, which can
damage DNA, and say the amount of gamma radiation the campion fruit
accumulated over 30,000 years is not much higher than that reported for a
1,300-year-old sacred lotus seed, from which a plant was successfully
germinated.
The Russian article was edited by Buford Price of the University of
California, Berkeley. Dr. Price, a physicist, chose two reviewers to
help him. But neither he nor they are plant biologists. “I know nothing
about plants,” he said. Ann Griswold, a spokeswoman for the National
Academy of Sciences, said the paper had been seen by an editorial board
member who is a plant biologist.
Tragedy has now struck the Russian team. Dr. Gilichinksy, its leader, was hospitalized with an asthma
attack and unable to respond to questions, his daughter Yana said on
Friday. On Saturday, Dr. Price reported that Dr. Gilichinsky had died of
a heart attack.
Eske Willerslev, an expert on ancient DNA at the University of
Copenhagen, said the finding was “plausible in principle,” given the
conditions in permafrost. But the claim depends on the radiocarbon date
being correct: “It’s all resting on that — if there’s something wrong
there it can all fall part.”
If the ancient campions are the ancestors of the living plants, this
family relationship should be evident in their DNA. Dr. Willerslev said
that the Russian researchers should analyze the DNA of their specimens
and prove that this is the case. However, this is not easy to do with
plants whose genetics are not well studied, Dr. Willerslev said.
If the claim is true, then scientists should be able to study evolution
in real time by comparing the ancient and living campions. Possibly
other ancient species can be resurrected from the permafrost, including
plants that have long been extinct.
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