A “fix and flex” model explains how plants breathe

New research published this week by University of Sheffield scientists is rewriting our textbook understanding of how plants breathe.

Plants “breathe” by taking up carbon dioxide and expelling oxygen through microscopic pores called stomata, which are surrounded by guard cells. The research proposes a new mechanism of how the stomata open. Carter

Textbook descriptions say that thickening of the inside of guard cells is an important part of the turgor [pressure]-driven shape change required for stomatal pore opening to occur. This interpretation is based on 19th century studies of the structure of the stomata rather than actual measurement of mechanical properties.

The new research, led by Professor Andrew Fleming in the Department of Animal and Plant Sciences at the University of Sheffield, used atomic force microscopy to show that although mature guard cells display the expected radial gradient of stiffness, this is not present in immature guard cells, yet young stomata show a normal opening response.

Professor Fleming explains, “Radial stiffening was thought to be really important for guard cells flexing from being relatively straight into a banana shape as they expanded, creating a pore between the two curved guard cells. However, immature guard cells don’t display a radial gradient of stiffness but the stomata still open. The textbook description can’t be true.”

Professor Jamie Hobbs, from the University’s Department of Physics and Astronomy and an expert in atomic force microscopy, explained further , “Our analysis also revealed an unexpected stiffening of the polar [end] regions of the stomata complexes, both in Arabidopsis and other plants (tomato and maize), suggesting that it is widespread across different plant species, therefore somehow important.

“By analysing the guard cells in detail and using computational modeling, we suggest that the polar stiffening reflects a mechanical pinning down of the guard cell ends which prevents stomata increasing in length as they open. This leads to an increased speed of pore opening and larger pores- you get ‘better’ stomata.”

With this new understanding of how plants breathe, the team is now exploring the possibilities of selecting and engineering crops that have improved mechanical properties in their stomata.

Professor Julie Gray from the Department of Molecular Biology and Biotechnology points out “Stomata play a central role in controlling how efficiently crops use water, a critical problem in many countries. Our study opens up a new avenue to improving agricultural productivity in some of the world’s most challenging environments.”

The research was a collaboration between biologists and physicists at the University of Sheffield, along with collaborators at the John Innes Centre in Norwich and the Sainsbury Laboratory at the University of Cambridge. It was funded through grants from the Leverhulme Trust, the Biotechnology and Biological Science Research Council and the Gatsby Charitable Foundation.

This full paper, “Stomatal Opening Involves Polar, not Radial, Stiffening Of Guard Cells”, is available on the Current Biology website.

For more information about this research, please contact Professor Andrew Fleming, a.fleming@sheffield.ac.uk or 0114 222 4830.

Notes to editors

The University of Sheffield
With almost 27,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities.

A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines.

Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in.

Sheffield is the only university to feature in The Sunday Times 100 Best Not-For-Profit Organisations to Work For 2016 and was voted number one university in the UK for Student Satisfaction by Times Higher Education in 2014. In the last decade it has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life.

Sheffield has six Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields.

Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.