Penn
State Intercom......April 19 , 2001
Focus on Research
Ozone ‘chokes up’ plants
By Barbara Hale
Public
Information
University researchers have identified how ozone, a major smog constituent, affects the microscopic breathingpores on plants' leaves, a process that may figure in the estimated $3 billion in agricultural losses caused by ozone air pollution in the United States each year.
Gro Torsethaugen, a postdoctoral researcher in the Environmental Resources Research Institute, said, "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 worked on the research project with Eva J. Pell, vice president for research and dean of The Graduate School, and Sarah M. Assmann, professor of biology.
Plants take in the carbon dioxide they need for photosynthesis through their stomates, Torsethaugen explained. 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 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, 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 said. "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. The researchers noted 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 exposure.
Barbara Hale can be reached at bah@psu.edu.
Visits now restricted
to all livestock units in Ag
As a precautionary measure to protect against foot-and-mouth and other contagious foreign animal diseases, the College of Agricultural Sciences has implemented a new biosecurity policy for all farm units housing livestock.
Effective immediately, visits to University dairy, beef, swine, sheep, deer and equine facilities will be by appointment only. All entrances to the restricted facilities will be posted. Appointments to visit the facilities may be requested by calling the College of Agricultural Sciences at (814) 865-1362 or by e-mailing coasvisits@lists.psu.edu.
Managers of the restricted farm units will interview potential visitors to determine the purpose of the visit. They also will request information to determine whether any of the visitors may have been in direct or indirect contact with any traveler from a country with confirmed cases of foot-and-mouth or other contagious foreign animal diseases. Other steps, including protective clothing and restrictions on direct contact with animals, will be implemented as appropriate for visitors who are cleared. All affected farm unit employees have been trained in the biosecurity protocols for handling livestock.
This policy will be in effect until further notice. New guidelines will be issued if and when conditions warrant. More information on foot-and-mouth disease is available at the College of Agricultural Sciences Foot-and-Mouth Disease Information Center on the Web at http://fmd.cas.psu.edu.
Drug mechanism
alters genetic makeup of virus
By Steve Sampsell
Public
Information
Researchers at the University have discovered a new mechanism for an existing antiviral drug that could permit the design and production of a new class of antiviral agents to treat RNA viruses.
Such viruses, a family that includes poliovirus and hepatitis C, use RNA as both their core genetic material and also to direct protein synthesis.
Research by a team led by Craig Cameron, assistant professor of biochemistry and molecular biology at University Park, reveals that ribavirin, a synthetic compound that inhibits RNA viruses by working at the cellular level, also possesses an ability to alter the structure of the viruses at the genetic level. Researchers used poliovirus as the experimental model.
"Our results indicate the antiviral effects of ribavirin come from its direct incorporation into the viral RNA," Cameron said. "When that happens, it changes the behavior of the base pairs of the RNA and the virus no longer produces faithful copies of itself. In that manner, ribavirin effectively shifts the internal balance of the virus and the virus suffers from a genetic meltdown."
While most organisms use DNA as their genetic material and RNA to direct protein synthesis, RNA viruses use RNA for both functions. When an RNA virus infects a cell, it directs the synthesis of proteins used to make copies of the original RNA and then uses those copies to build the chromosomes of the virus. Many RNA viruses can be stopped by intervention from the immune system or with the help of vaccinations. Others adapt, developing their own "quasispecies" so rapidly that neither the immune system nor vaccinations provide relief.
In general, RNA's instability -- when compared to DNA -- means it works well as a virus because it changes form, or mutates, often enough to prevent the immune system from providing effective antiviral activity. With ribavirin acting at the genetic level, researchers have discovered a way to use the mutations against the virus. Ribavirin capitalizes on the mutations and stops the virus by altering its genome, upsetting its delicate balance, and forcing it to collapse upon itself.
Collaborators with Cameron were: Jamie Arnold and David Maag from Penn State; Raul Andino and Shane Crotty from the University of California at San Francisco; and Zhi Hong, Johnson Lau, and Weidong Zhong from Schering-Plough Research Institute in Kenilworth, N.J.
Steve Sampsell can be reached at sws102@psu.edu