Researchers seek alternative to ozone depleting pesticide; collaboration key to success

Harinder Singh is working on the transfer of parasitic
nematode worms to test programmed cell death genes.
Esteban Cortez / The Collegian

Plant parasites do over $120 billion per year in damage to worldwide agriculture.  Chemicals are available to eradicate these parasites, but they present safety problems.

Fresno State biology professor Dr. Alejandro Calderon-Urrea is searching for an alternative to methyl bromide, a previously used pesticide that caused damage to the ozone layer.  He has identified a promising alternative, a type of organic compound with significant biological functions.

The parasites being targeted are nematode worms, which can badly damage the roots of plants.

“In a collaboration with Dr. Saeed Attar from chemistry, we developed some organic chalcones that seemed to have some specific deleterious effects against plant-parasitic nematodes,” Calderon-Urrea said.

These chalcones are a type of “pesticide” that will harm only the targeted nematode worms.  Methyl bromide was harmful to humans and parasites.

Calderon-Urrea has tested the specifically engineered chemicals with two similar types of nematode worms.

“These chemicals seemed to kill the plant parasitic nematodes very well,” Calderon-Urrea said.

Calderon-Urrea has used specific programmed cell death genes in the past to kill nematode worms, but has now begun this new experiment because his previous project is in the process of being published in a scientific journal. The investigation is focused on finding the minimum amount of chemical that can be used to eliminate the parasite.

The idea for the whole project started in 2001 during a coffee break between Attar, now the chemistry department chair and researcher and Calderon-Urrea.  Attar noticed during a laboratory course he was teaching that some students had developed slight skin irritations after performing an experiment involving chalcones.

After a search through the published chemical literature, Attar found that chalcones had been reported to have a variety of biological— including nematocidal [parasite killing]— activities, and the collaboration began.

“The idea was to find something to replace methyl bromide. These chalcones have two benzene rings. My idea was to replace one of the benzene rings with an iron-containing group called ferrocene,” Attar said.

Zach O’Brien, a graduate student in Attar’s lab and now a Ph.D. student at UCLA, made the first ferrocenyl derivatives of these chemicals, and in the middle of this, Hasan Al-Haddad, an undergraduate student in Calderon-Urrea’s lab and now a Ph.D. student at UC Davis, got involved and did parallel studies with an organic set of similar chemicals for comparison.

Attar and those collaborating with him ultimately made 63 variations of the new chemical.  The more active of these were organic analogs.  The eight most deadly to nematodes are now being studied 11 years later while a full-length paper has recently been published in the Journal of Bioorganic and Medicinal Chemistry.  Attar commented on the collaboration between himself and Calderon-Urrea, saying, “I have always been interested in biology and consider myself a biologically oriented organic chemist. I was a biology minor and a chemistry major in college… these projects are at the interface between chemistry and biology.”

“It’s been very fruitful, and I look forward to more research we can do together.  Regardless of an undergraduate’s major and future career plans, they will learn a lot by performing scientific research. What you do is not as important as your enthusiasm.  Generally speaking, the physical setting of the CSU departments such as Biology and Chemistry allows these collaborations to happen.”

Researchers at Fresno State are now testing whether the eight active chemicals can affect the growth of other microorganisms found in the soil. Calderon-Urrea and Attar want to find a chemical that will only affect the parasites, leaving all other organisms unharmed because the chemical will essentially be used as a pesticide.

Preliminary studies have been run by undergraduate students with the last names of Ponce, Hill and Serrano from an NSF–funded project, for which Dr. Dave Andrews is the principal investigator. These students, as well as U.C. Merced research associate Venu Polineni and Harinder Singh from Calderon-Urrea’s lab, have been working to collect data and analyze the results.

“Methyl bromide is causing problems with the ozone layer.  All of these questions push us toward specific environmentally friendly techniques. The harm will be specifically toward this nematode,” Singh said.

Singh has worked on testing programmed cell death genes in the past.  These genes basically hold a code which tells the cell to destroy itself. Cancer can occur when this mechanism is interrupted in normal cells.  When these genes are incorporated into a plant which the parasitic nematode eats, a large number of cells in the nematode die, killing the parasite.

Testing of human cells is also under way.  An on-campus cancer laboratory found negative effects on human cells.

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