Researchers Find 320 Million-Year-Old Plant Root Stem Cells

It may look more like a shiny mosaic or a piece of jewellery, but the world’s oldest plant stem cells contain a 320 million-year-old fossil. And it gives us an entirely new understanding of the evolution of how plants grow.

The fossil shows that the way plants grew from their roots millions of years ago was totally different from the way many modern plants form. Stem cells, self-renewing cells responsible for the development of multicellular organisms, in groups called meristems, are present in plants at the tips of shoots and roots.

Scientists at Oxford University have discovered the oldest known population of plant root stem cells in a 320 million-year-old fossil. The researchers found the 320 million-year-old stem cells are different to all those living today, revealing a unique pattern of cell division that had remained unknown until now.

This means some of the mechanisms controlling root formation in plants and trees back then have now become extinct.

The fossils were the remains of the soil from the first giant tropical rainforests on Earth. These fossils made up the rooting structures of the plants growing in the Earth’s first global tropical wetland forests.

The cells, which gave rise to the roots of an ancient plant, were found in a fossilized root tip held in the Oxford University Herbaria – a preserved selection of plants kept for scientists to study.

‘I was examining one of the fossilized soil slides held at the University Herbaria as part of my research into the rooting systems of ancient trees when I noticed a structure that looked like the living root tips we see in plants today,’ said Alexander Hetherington, from Oxford University, who made the discovery during the course of his research.

‘I began to realize that I was looking at a population of 320 million-year-old plant stem cells preserved as they were growing – and that it was the first time anything like this had ever been found.

‘It gives us a unique window into how roots developed hundreds of millions of years ago.’ This is the first time an actively growing fossilized root has been discovered.

The soil was preserved in the rock that formed in the Carboniferous swamps which gave rise to the coal sources spanning what is now Appalachia to central Europe.

This includes the coalfields in Wales, northern England, and Scotland. Because of this, Mr. Hetherington has named the stem-cell fossil Radix carbonica, which is Latin for ‘coal root’.

The forests had trees over 164 feet (50 meters) tall, and were in part responsible for one of the most dramatic climate change events in history.

When deep rooting systems evolved, this increased the rate of chemical weathering of silicate minerals in rocks – a chemical reaction that pulled carbon dioxide out of the atmosphere. This led to the cooling of the Earth and one of the planet’s great ice ages.

Professor Liam Dolan, Head of the Department of Plant Sciences at Oxford University and senior author of the paper, said ‘these fossils demonstrate how the roots of these ancient plants grew for the first time.

‘It is startling that something so small could have had such a dramatic effect on the Earth’s climate.

‘This discovery also shows the importance of collections such as the Oxford University Herbaria – they are so valuable, and we need to maintain them for future generations.’