Explaining how ozone "chokes up" plants

December 05, 1999

University Park, Pa. --- Penn State researchers have identified how ozone, a major smog constituent, affects the microscopic breathing pores on plants' leaves, a process that may figure in the estimated $3 billion in agricultural losses caused by ozone air pollution in the U.S. each year.

Dr. Gro Torsethaugen, a postdoctoral researcher in Penn State's Environmental Resources Research Institute, says, "Although elevated ground levels of ozone resulting from traffic and other fossil fuel burning have long been associated with losses in agricultural yield, the precise cellular targets of ozone's action were essentially unknown. Our work has shown, for the first time, that, rather than causing the pores or stomates on a plant's leaves to close, as was generally assumed, ozone actually inhibits stomatal opening by directly affecting the 'guard cells' that control the opening."

Torsethaugen adds that knowing ozone's specific cellular targets may make it possible in the future to breed or to genetically engineer new plant varieties to improve productivity in geographic regions, such as California, with significant ozone exposure.

Torsethaugen and her co-authors Dr. Eva J. Pell, the Steimer professor of agricultural sciences, and Dr. Sarah M. Assmann, professor of biology, published their findings in a recent issue of the Proceedings of the National Academy of Sciences (PNAS).

Plants take in the carbon dioxide they need for photosynthesis through their stomates, Torsethaugen explains. They also release oxygen made in photosynthesis through the same pores. Ozone can also enter the plant through the stomates and can affect photosynthesis via that route. The Penn State experiments point to direct action on the guard cells as an additional path that ozone takes to decrease carbon dioxide assimilation and reduce plant productivity.

Torsethaugen conducted the experiments with fava bean plants, an important world food source and a species scientists favor for guard cell studies. Using various techniques, she examined the pores on the leaves of whole plants and portions of leaf surfaces and then studied the isolated guard cells.

In whole plants and the leaf surfaces, she found that ozone directly affects the stomatal opening.

Using isolated guard cells, she monitored the flow of potassium, in a positively charged or ion form, into and out of the cells.

"We monitored potassium because it is a major component in the osmotic process," she says. "If the potassium ion concentration is increased, water comes into the cell by osmosis and the guard cells surrounding the stomate swell. This swelling causes the pore to open."

Ozone exposure reduced the flow of potassium ions into the guard cells but did not affect the outward flow, indicating that ozone inhibits the opening of the pores.

In their PNAS paper, the authors note that their findings may have particular relevance during drought. They write, "Stomatal closure during a period of drought may be less readily reversed in ozone-exposed plants. This may be particularly relevant because the highest ozone concentrations are sometimes associated with times of drought."

In addition, they write "In major agricultural regions with high light environments and significant ozone exposure - e.g. the "South Coast Air Basin of California, which has the most extreme ozone levels in the U.S. - midday stomatal closure often occurs because of the low ambient humidity that results from the high light, high temperature conditions of midday. Because the generation of ozone in photochemical smog depends on high solar irradiation, ozone inhibition of stomatal opening could significantly retard stomatal reopening in the afternoon after this mid-day depression and consequently reduce crop yield."

Identification of the potassium ion channel as a target for ozone action opens the door to selectively breeding or genetically engineering less ozone sensitive plants to improve plant productivity in geographic regions with significant ozone expose.

However, the Penn State researchers also note that "Our identification of a specific ion channel as a target for ozone action may prompt comparable studies in mammalian system, leading to improved understanding of and treatment for the disease etiologies exacerbated by ozone. "

The research was supported in part by a grant from the Binational Agricultural Research and Development/U.S. Department of Agriculture. The Department of Biology, University of Oslo, Norway, where Torsethaugen earned her doctorate, provided additional support.
-end-
EDITORS: Dr. Torsethaugen is at 814-865-0680 or gxt6@psu.edu by email.

Penn State

Related Photosynthesis Articles from Brightsurf:

During COVID, scientists turn to computers to understand C4 photosynthesis
When COVID closed down their lab, a team from the University of Essex turned to computational approaches to understand what makes some plants better adapted to transform light and carbon dioxide into yield through photosynthesis.

E. coli bacteria offer path to improving photosynthesis
Cornell University scientists have engineered a key plant enzyme and introduced it in Escherichia coli bacteria in order to create an optimal experimental environment for studying how to speed up photosynthesis, a holy grail for improving crop yields.

Showtime for photosynthesis
Using a unique combination of nanoscale imaging and chemical analysis, an international team of researchers has revealed a key step in the molecular mechanism behind the water splitting reaction of photosynthesis, a finding that could help inform the design of renewable energy technology.

Photosynthesis in a droplet
Researchers develop an artificial chloroplast.

Even bacteria need their space: Squished cells may shut down photosynthesis
Introverts take heart: When cells, like some people, get too squished, they can go into defense mode, even shutting down photosynthesis.

Marine cyanobacteria do not survive solely on photosynthesis
The University of Cordoba published a study in a journal from the Nature group that supports the idea that marine cyanobacteria also incorporate organic compounds from the environment.

Photosynthesis -- living laboratories
Ludwig-Maximilians-Universitaet (LMU) in Munich biologists Marcel Dann and Dario Leister have demonstrated for the first time that cyanobacteria and plants employ similar mechanisms and key proteins to regulate cyclic electron flow during photosynthesis.

Photosynthesis seen in a new light by rapid X-ray pulses
In a new study, led by Petra Fromme and Nadia Zatsepin at the Biodesign Center for Applied Structural Discovery, the School of Molecular Sciences and the Department of Physics at ASU, researchers investigated the structure of Photosystem I (PSI) with ultrashort X-ray pulses at the European X-ray Free Electron Laser (EuXFEL), located in Hamburg, Germany.

Photosynthesis olympics: can the best wheat varieties be even better?
Scientists have put elite wheat varieties through a sort of 'Photosynthesis Olympics' to find which varieties have the best performing photosynthesis.

Strange bacteria hint at ancient origin of photosynthesis
Structures inside rare bacteria are similar to those that power photosynthesis in plants today, suggesting the process is older than assumed.

Read More: Photosynthesis News and Photosynthesis Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.