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Sscientists develop an improved theory on leaf gas exchange

by: Natalia Bateman, CoETP

Scientists studying how leaves gain and lose water during the process of photosynthesis, have developed a more precise theory that could help future research on crop resilience to drought and heat waves.

Until now scientists assumed that the movement of carbon dioxide (CO₂) and water happened mostly through the pores of the leaves or stomata, so current models focus mainly on these structures, overlooking the role of the leaf skin, called the cuticle.

“Current leaf models focus on the stomata to understand how water moves out and in the plant. This is a good approximation most of time, but not always. When you study plants under heat stress or drought conditions, you realise that by ignoring the role of the cuticle, you are missing half of the story,” says lead researcher Diego Márquez, from the ARC Centre of Excellence for Translational Photosynthesis (CoETP), located at ANU.

“In our study, we present a more realistic and detailed approach to understand how the leaf works by considering the small but very important fluxes happening through the cuticle of the leaf. If we want to understand how plants would be able to endure the expected consequences of climate change, we cannot overlook the cuticle anymore,” says Márquez.

Plants take carbon dioxide (CO₂) from the atmosphere to produce food and in the process, they lose water.

The cuticle of the leaf is almost impermeable to CO₂, so the main access for this gas into the leaf is through stomata. Water on the other hand, can go easily through the cuticle. This means that If stomata are closed (for example during the night), the plant continues losing water through the cuticle.

Previously, the fluxes through the cuticle were considered too small to be important. In the study, published recently in the journal Nature Plants, the scientists provide a mathematical tool to start accounting for the two pathways – the pores and skin. This new perspective improves the widely used theory for gas exchange proposed in 1981, which does not account for the fluxes of the cuticle.

‘Scientific models are dynamic: they are there to question the world and get closer to reality, in this case, about how plants manage water. By including the cuticle in the mathematical calculations we created 40 years ago, we are bringing our model closer to the real world.” says co-author Professor Graham Farquhar, CoETP Chief Investigator and one of the authors of the initial model on gas exchange.

“We hope this improved version of the model is going to give a common language for scientists working on different aspects of the cuticle including its chemistry, physics and biology and how they are connected, so we can understand how water crosses thought the cuticle,” Professor Farquhar says.

The improved mathematical model includes the small fluxes of the leaf cuticle

“Our next step is to develop a simple standard technique for researchers to help them measure cuticle conductance. It is a simple method that can become a routine for researchers, so from now on they can start accounting for it,” says co-author Hilary Stuart-Williams from the CoETP at the Research School of Biology in ANU.

This research was funded by the ARC Centre of Excellence for Translational Photosynthesis, which aims to improve the process of photosynthesis to increase the production of major food crops such as sorghum, wheat and rice. The project was also funded by the CONICYT Doctorado Becas Chile.

The paper was published in the Nature Plants Journal and is available to view online at:

https://www.nature.com/articles/s41477-021-00861-w

Márquez, D.A., Stuart-Williams, H. & Farquhar, G.D. An improved theory for calculating leaf gas exchange more precisely accounting for small fluxes. Nat. Plants (2021). https://doi.org/10.1038/s41477-021-00861-w

Read the ANU Media release here: Scientists-show-drought-tolerant-crops-need-skin-in-the-game

Reflecting on the research process that resulted on this paper

PhD student Diego Márquez, reflects on the process that finalised in the publication of this article in the journal Nature Plants.

This story, as all PhD projects, started with a question, but also with what initially seemed like a failure. I wanted to understand how plants behave under different water conditions, so I started my project by measuring gas exchange through the leaves. However, my measurements keep coming with an error that was really bothering me.

Credit: Florian Busch, CoETP

For months, I thought I was doing something wrong, as the data didn’t make sense. I tried different machines to measure gas exchange on leaves and frustratingly, the problem kept appearing everywhere.

This pushed my team and I to face the problem, instead of ignoring it. In the earlier version of the mathematical model that describes gas exchange on leaves, this “error” was assumed as a problem that you had to live with. We started wondering if the long-ignored cuticle fluxes had to do something with it. We included them in our mathematical calculations and Eureka, it worked!

The information that didn’t make sense was due to the small fluxes of water that happen through the skin of the leaf. We finally were able to understand the puzzling gas exchange differences we were encountering between the lower and the upper side of the leaves. In a more global scale, we can now also explain why we can see that plants in a forest lose water during the night when the stomata are closed. Now we know this is because the plant is not using the stomata as a main channel of gas exchange but it is using its cuticle.

I think our study highlights three important aspects of research that are sometimes dismissed:

1) that failures can make research advance and be the source of Eureka moments,

2) that you have to face problems instead of ignoring them, and

3) A team of people are needed for ideas to grow; people that permit and push you to try new things and see them from different perspectives.

FOR INTERVIEW:

Dr Diego Márquez

ARC Centre of Excellence for Translational Photosynthesis

T: +61 6125 0123  Twitter: @DiegoMa_rquez

E: diego.marquez@anu.edu.au

Professor Graham Farquhar

Chief Investigator Centre of Excellence for Translational Photosynthesis

e-mail: Graham. Farquhar@anu.edu.au Twitter: @GrahamFarquhar

For media assistance, contact:

Natalia Bateman

Communications Officer, ARC Centre of Excellence for Translational Photosynthesis

Phone: +61 02 6125 1703 m. 0401 083 380

e-mail: natalia.bateman@anu.edu.au