TeaThe longest-lived leaves in the plant kingdom can be found only in the harsh, hyperrid deserts that straddle the border between southern Angola and northern Namibia.
A desert, of course, isn’t the most hospitable place for living things to grow, let alone leafy greens, but the Namib Desert—the world’s oldest, with less than 2 inches of rainfall a year—is where Welwitschia says home.
In Afrikaans, the name of the plant is “tweeblarknidood”, which means “two leaves that cannot die”. The nomenclature is apt: Welwitschia grows only two leaves – and continuously – in a lifespan that can last for millennia.
“Most plants develop a leaf, and that is it,” says Andrew Leach, a plant geneticist at Queen Mary University in London. “This plant can live for thousands of years, and it never stops growing. When it stops growing, it’s dead.”
Some of the largest plants are believed to be over 3,000 years old, the two leaves growing continuously since the beginning of the Iron Age, when the Phoenician alphabet was invented and David was crowned King of Israel .
By some accounts, Welwitschia isn’t much to see. Its two fibrous leaves, dampened by dry desert winds and fed by thirsty animals, become shriveled and twisted over time, giving Welwitschia a distinctive octopus-like appearance. A 19th-century director at Kew Gardens remarked, “It is the most wonderful plant ever brought into this country and one of the ugliest plants.”
But since it was first discovered, Welwitschia has fascinated biologists including Charles Darwin and botanist Frederick Welwitsch, after whom the plant is named; It is said that when Welwitsch first came to the plant in 1859, “he could do nothing but kneel on the burning soil and look at it, half afraid that a touch might prove it to be a figment of imagination.” “.
In a recently published study nature communicationIn this article, researchers report some of the genetic secrets behind Welwitschia’s unique size, extreme longevity and profound resilience.
Jim Leibens-Mack, a plant biologist at the University of Georgia who was not involved in the study, says it “gives us a basis for better understanding how Welwitschia does all the crazy stuff that it does”.
The Welwitschia genome reflects the arid and nutrient-poor environment of the plant. And its genetic history appears to be consistent with environmental history.
About 86 million years ago, following a fault in cell division, the entire Welwitschia genome region doubled in periods of increased aridity and prolonged drought — and likely formed the Namib Desert, says Tao Wan, a botanist at Fairey. Lake Botanical Garden in Shenzhen, China, and lead author of the study. He says that “excessive stress” is often associated with such genome duplication events.
Leach, a co-author of the study, says that even the duplicated genes are stripped of their original functions, potentially taking on new ones.
However, having more genetic material comes with a cost, Van says.
“The most basic activity for life is DNA replication,” he says, “so if you have a large genome, it’s really energy consuming to sustain life,” especially in such a harsh environment.
To make matters worse, a significant amount of Welwitschia’s genome is “junk” self-replicating DNA sequences called retrotransposons.
“Now that junk needs to be replicated, repaired,” Leach says.
The researchers traced an “explosion” of retrotransposon activity to 1 to 2 million years ago, most likely due to an increase in temperature. But to counteract this, widespread epigenetic changes occurred in the Welwitschia genome that silenced the junk DNA through a process called DNA methylation.
This process, along with other selective forces, significantly reduced the size and energetic maintenance cost of Welwitschia’s duplicate library of DNA, Van says, giving it “a very efficient, low-cost genome.”
The study also found that other genetic changes were hidden in Welwitschia leaves.
The leaf of the average plant grows from the top of the plant, or the tippy-top of its stem and branches. But the original growing tip of Welwitschia dies, and the leaves emerge from a vulnerable area of the plant’s anatomy called the basal meristem, which supplies fresh cells to the growing plant, Van says. The greater number of copies or increased activity of certain genes associated with efficient metabolism, cell growth and stress resilience in this region may help it to thrive under extreme environmental stress. In a warming world, the genetic lesson that Welwitschia has to offer could help humans produce tougher, less thirsty crops.
“When we see that the plant is able to live in this environment for so long and preserve its DNA and its proteins, I really feel like we can find clues to improve agriculture,” said Leibens- Mack says.
The study also underscores the importance of curiosity-driven research. When you face two leaves growing in a desert against all odds, kneel in the burning mud and take a closer look.
“With strange things, you discover strange things that help you understand things you didn’t know you didn’t understand,” says Leach.
This article originally appeared in the new York Times
Credit: www.independent.co.uk /