How plants breathe and how humans shaped their ‘lungs’

Scientists have discovered how plants create networks of air channels – the lungs of the leaf – to transport carbon dioxide (CO2) to their cells.

The development of stomata and leaf airspace must be composed to set up a proficient and powerful network that enables gas exchange for photosynthesis. Yet, it wasn’t known how those channels form in the right places in order to provide a steady flow of CO2 to every plant cell.

Scientists at the University of Sheffield‘s Institute for Sustainable Food, in a new study used genetic manipulation methods to uncover that the more stomata a leaf has, the more airspace it forms. The channels act like bronchioles – the tiny sections that convey air to the exchange surfaces of human and animal lungs.

Scientists also have shown that the movement of CO2 through the pores most likely determines the shape and scale of the air channel network.

This discovery is expected to provide detail information on the internal structure of a leaf and how the function of tissues can influence how they develop.

The study also shows that wheat plants have been bred by generations of people to have fewer pores on their leaves and fewer air channels, which makes their leaves denser and allows them to be grown with less water.

Confocal overview of a TaEPF1 OE wheat leaf showing epidermal layer (purple), subtending mesophyll cells (green), a stomate (St) consisting of guard cells and associated subsidiary cells and, in the same file, an arrested stomatal precursor.  CREDIT University of Sheffield
Confocal overview of a TaEPF1 OE wheat leaf showing epidermal layer (purple), subtending mesophyll cells (green), a stomate (St) consisting of guard cells and associated subsidiary cells and, in the same file, an arrested stomatal precursor.
CREDIT
University of Sheffield

This new insight features the potential for scientists to make staple crops like wheat even more water-efficient by altering the interior structure of their leaves. This methodology is being pioneered by other scientists at the Institute for Sustainable Food, who have created climate-ready rice and wheat which can survive extreme drought conditions.

Professor Andrew Fleming from the Institute for Sustainable Food at the University of Sheffield said: “Until now, the way plants form their intricate patterns of air channels has remained surprisingly mysterious to plant scientists.

“This major discovery shows that the movement of air through leaves shapes their internal workings – which has implications for the way we think about evolution in plants.

“The fact that humans have already inadvertently influenced the way plants breathe by breeding wheat that uses less water suggests we could target these air channel networks to develop crops that can survive the more extreme droughts we expect to see with climate breakdown.”

Dr Marjorie Lundgren, Leverhulme Early Career Fellow at Lancaster University, said: “Scientists have suspected for a long time that the development of stomata and the development of air spaces within a leaf are coordinated. However, we weren’t really sure which drove the other. So this started as a ‘what came first, the chicken or the egg?’ question.

“Using a clever set of experiments involving X-ray CT image analyses, our collaborative team answered these questions using species with very different leaf structures. While we show that the development of stomata initiates the expansion of air spaces, we took it one step further to show that the stomata actually need to be exchanging gases in order for the air spaces to expand. This paints a much more interesting story, linked to physiology.”

The Director of the Facility, Professor Sacha Mooney, said, “The X-ray imaging work was undertaken at the Hounsfield Facility at the University of Nottingham. Until recently the application of X-ray CT, or CAT scanning, in plant sciences has mainly been focused on visualizing the hidden half of the plant – the roots – as they grow in soil.”

“Working with our partners in Sheffield we have now developed the technique to visualize the cellular structure of a plant leaf in 3D – allowing us to see how the complex network of air spaces inside the leaf controls its behavior. It’s very exciting.”

The study is published in the journal Nature Communications.

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