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How Did Plants Happen? At Last, We May Have an Answer



  • by Diana O. Potter

As vegans, we depend on plants for our food, our environment — our very existence. And we’re so used to having them around, we don’t question their existence. They’re just here, like us.

But, like everything else on Earth, including us, they didn’t have to arise from the primordial soup. And for years scientists have labored to discover how they did.

Now they believe they may know. And if you think human evolution is impressive, wait ‘til you hear this.

A World Without Plants Becomes Our Earth Because of Them

For billions of years, as our Earth cooled and oceans and land masses formed, there were no living things, including plants, on the barren, rocky land. Yet today, after their beginnings some 500,000 years ago, so-called land plants account for almost all the Earth’s biomass — a fancy term for living organisms — including some 500 billion tons of carbon, more than four times the amount accounted for by all other living things, combined.

There’s more: Land plants are also the reason we have soil to grow them in, oxygen to breathe, and animals who can live on land because they were able to develop from ancient life forms in the seas (including us!).

Scientists have known for a long time that land animals evolved from ancient sea creatures. They naturally suspected that land plants developed the same way, but despite years of research, they were unable to find out how — until now.

On November 14, 2019, researchers at the University of Alberta in Canada and the University of Cologne in Germany reported they believe they’ve cracked the mystery, using the science of genetics.

Solving the Mystery — With a Surprising Discovery

First you need to know that once plants covered the land, they left a lot of fossils that might have offered the scientists help in tracing land plant evolution. But the very earliest land plants weren’t documented well enough to be helpful. So according to an article in The New York Times, the scientists decided to work with living organisms, especially their DNA, to find the answers they were seeking.

Algae soon took center stage.

The researchers discovered that two species of a freshwater algae group with a very long name — Zygnematophyceae — had some of the key genes land plants need to grow and thrive. When the researchers sequenced the complete genomes of these algae, they found that one set of genes stood out.

Why, you ask? Because the algae had apparently “stolen” the genes from bacteria, and not just any bacteria: These live in soil today, helping plants survive potentially damaging stresses such as drought. They even help today’s plants make seeds and spores that can remain dormant (alive but not growing) for months or even years.

What was there about these bacterial genes in the two Zygnematophyceae species that made them able to help plants grow and thrive? Well, what two factors do plants need most to grow and thrive?

You’re right: sunlight and carbon dioxide.

What the Researchers Think Happened

Billions of years ago, according to the researchers, earlier forms of these bacteria, which lived in the ocean and were able to capture sunlight and carbon dioxide, appear to have been acquired by ancient amoeba-like organisms that evolved over millennia into algae.

Fine, you say. But how did the bacterial genes get into the DNA of the Zygnematophyceae algae, energizing millions of years of land plant evolution? Answer: The researchers aren’t yet sure, but they make a strong case for the following explanation:

  • The algae formed a carbohydrate-rich sponge-like coat, which soaks up water.
  • Bacteria fed on the coat carbohydrates, in return producing vitamins that may have benefited the algae.
  • During this process, genes from the bacteria may have entered the algae’s DNA.

Makes sense, but proving it will be difficult and take a long time, the researchers note.

That’s okay with me, and likely with you, too. We’re just glad the plants are here in such abundance, variety, and power to nourish the planet, right?

But it is nice to know at least something of how that may have happened. Stay tuned!

Click here to learn more about the researchers’ work.

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