Mystery of how plants adapted to life on dry land solved

Study shows that plants restrict tissue width to promote drought resistance

For prehistoric vascular plants to grow taller, they had to evolve. Getty
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Prehistoric plants made dramatic changes that have allowed the modern green world to develop and could provide help in tackling climate change.

Research published on Thursday reveals a key adaptation that allowed plants to colonise on dry land and explains how vascular plants avoid having blocked stem tissue as they grow bigger.

It also helps settle a question raised 100 years ago when scientists first identified “elongated, narrow, and increasingly complex shapes” in vascular plants, but did not know why.

The finding, published in the journal Science, offers hope for advances in environmental work such as trying to ensure drought-resistance in crop breeding programmes as the climate changes.

The first vascular plants were just centimetres tall and constrained to live near water because of the blocked tissues problem. Stem tissue became blocked if they grew too tall.

To grow taller, they had to evolve alternatives. Plant lineages that succeeded on land found their own solution to the problem.

The new study shows that plants maintain drought-resistant vascular arrangements by restricting the tissue’s width.

With increased size, tissue assumed the elongated, narrow and increasingly complex shapes that were first identified — but not explained — in 1920.

“If they are strung out in a long narrow shape, embolism [blockage] has to overcome many successive cell walls to go very far, which can save the plant’s life in a drought,” said study co-author Dr Martin Bouda.

Co-author Professor Craig Brodersen said: “Now that we have a better understanding of how the vascular systems are put together and how that influences a plant's ability to tolerate drought, that's the kind of thing that could be used as a target for breeding programmes.”

The fossil record shows increasing diversity in how the plant stem is assembled as plants radiate out from water sources.

Vascular tissue arrangements diversify to take on a vast array of shapes in the stem.

The team of scientists sampled the xylem strands of living and extinct seedless vascular plants spanning over 400 million years of evolution.

Updated: November 10, 2022, 7:00 PM
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