"The cultivation of offspring from old seeds radiocarbon dated at between 200 and 500 years of age is a first in plant biology," said UCLA research biologist Jane Shen-Miller, lead author of the research, published in the February issue of the American Journal of Botany.
Shen-Miller led a team that traveled in 1996 to the village of Xipaozi in Pulandian, Liaoning province, China, to search for ancient lotus seeds. Shen-Miller's team combed the land -- which dried over the centuries due to a series of massive earthquakes (a 1556 earthquake in the region killed more than 800,000 people) -- and collected 20 lotus seeds and soil from the region. "Looking for the seeds was like walking back into history," she said.
To the researchers' surprise, all four of the lotus seeds that were tested for viability germinated -- all between 200 and 500 years old -- and showed abnormalities, particularly in their leaves, stalks and underground stems.
"All the offspring of the old lotus seeds are abnormal," Shen-Miller said. "Instead of standing up straight with strong leaves, these were smaller, the leaves were weak and bent, displayed abnormalities in color, and the underground stems were small and not getting enough food."
What accounts for these changes?
All soils are radioactive, Shen-Miller said. The soil the lotus seeds were found in emits low doses of potentially harmful, mutation-causing radiation, which Shen-Miller said "most likely" is the cause of the abnormalities that are similar to those in other plants irradiated experimentally.
"It's startling that they were all abnormal with such a low dose of radiation exposure," Shen-Miller said. "Human cancer patients receive 20 times as much radiation in one day as the lotus seeds get in hundreds of years."
Regardless of the abnormalities, the long-term low-dose radiation does not affect lotus seed germination; they still sprout. This research represents the longest natural experiment of low-dose radiation ever recorded, and the first time scientists have seen examples of the effects of radiation exposure over centuries.
Research on the lotus seeds may have important implications for aging in other organisms, the researchers said, who believe the lotus must have a powerful genetic system to repair germination defects arising from hundreds of years of aging.
"The lotus is so robust that it can sprout after centuries of exposure to low-dose gamma radiation," Shen-Miller said. "We need to learn about its repair mechanisms, and about its biochemical, physiological and molecular properties. The repair mechanisms in the lotus would be very useful if they could be transferred to crops, such as rice, corn and wheat, whose seeds have life spans of only a few years."
Shen-Miller led a UCLA research team that recovered a viable lotus seed more than 1,200 years old from the same lakebed in China -- the oldest living seed whose date could be established, in research published in 1995.
The lotus plant is known from the geologic record as early as 135 million years ago, "dating from a time when dinosaurs roamed the Earth," Shen-Miller said. In China, it has been grown for at least 4,000 years.
Shen-Miller said she would share her remaining ancient lotus seeds with other interested biologists.
Her colleagues on the research include UCLA paleobiologist J. William Schopf, director of UCLA's Center for the Study of Evolution and the Origin of Life; Garman Harbottle, a chemist at Brookhaven National Laboratory; John Southon, a chemist at Lawrence Livermore National Laboratory; and a team of geologists from Beijing, Nanjing and Dalian, China.