Parasitic plants sniff out hosts

September 28, 2006



Parasitic plants do not haphazardly flail about looking for a host but sense volatile chemicals produced by other plants and identify potential hosts by their emissions, according to a team of Penn State chemical ecologists.

"We are interested in how plants respond to their environment, and have looked at plant insect interactions," says Dr. Consuelo M. De Moraes, assistant professor of entomology. "It was surprising to see how little was available on how above-ground parasitic plants find their hosts from far-off."

The researchers looked at Cuscuta pentagona, field dodder or five angle dodder, a plant that infests a variety of crops including tomatoes, carrots, onions, citrus trees, cranberries and alfalfa and reported their finding in today's (Sept. 29) issue of Science. Dodder grows throughout the world and is a difficult pest to eliminate because chemicals that kill the parasite also often kill the host plant.

"There is currently no reliable way to get rid of these pests," says Justin B. Runyon, graduate student in entomology. "It is estimated that in California each year, a 20 percent infestation of the tomato crop reduces yield by 25 percent and causes a loss of 4 million dollars."

The researchers used a variety of experiments to determine how newly emerging dodder shoots find a host. The length of time these parasites can live without a host is determined by the amount of food stored in the seed, but they can only grow about four inches before they die.

"These plants have no roots and barely have leaves and the flowers are very tiny," says Mark C. Mescher, assistant professor of entomology.

First the researchers placed dodder seedlings in a water vial at the center of a filter paper disk. A tomato plant was placed near the edge of the disk and the dodder plant was allowed to grow and attempt to locate its host. Dodder plants search for hosts by growing and moving in a circular pattern. In the past, many assumed that the search was random and the location of a host simply a chance encounter. After four days, when the plant was growing flat on the filter paper, the researchers measured the direction of the shoot.

The researchers report that 80 percent of the dodder plants grew onto the side of the filter paper nearest the tomato, with many growing directly towards the tomato plant. Statistical analysis provided strong evidence for directed growth by dodder, but did not indicate what causes the directionality.

The Penn State researchers then challenged dodder seedlings with artificial tomato plants, pots of moist dirt, and vials of green or red water. None of these objects elicited any directional growth. Then, to narrow down the possible cues being used, they tested the seedlings' response to tomato plants slightly separated from the dodder seedlings, out of view so to speak, in a set-up designed to block possible light cues. The researchers observed a growth response toward the tomato plants similar to that in their first experiment. Finally, to firmly establish that volatile chemicals from the host plant were causing this response, the researchers used the same set-up to examine the response to extracted host volatiles, using a solvent-only sample as a control in the opposite direction. They again observed a strong growth response toward the tomato volatiles.

"This showed that host volatiles elicit a growth response in the absence of any other plant-derived clues," says Mescher. "However, while volatile chemicals might be key, our results do not rule out the possibility that other cues such as light or shade may play a role."

After establishing the role of volatiles in leading the parasite plants to their tomato hosts, the researchers looked at other potential hosts including wild impatiens, and showed that the parasites were attracted to a wide variety of plants. They even found attraction to wheat plants, a poor host on which the dodder seedlings do not survive. However, when the researchers offered the seedlings a choice between wheat and tomato plants, the tomato won out, indicating that the parasites have some way of deciding between a good host and a bad host.

The researchers examined responses to some of the individual compounds released by host plants. Of seven compounds tested from tomato, three caused a directional growth response in dodder. One of these chemicals is also released by wheat, which might explain why wheat is somewhat attractive despite being a poor host. However, another chemical compound from wheat actually repels the dodder seedlings, perhaps explaining why the odor of wheat is less attractive than that of the preferred host tomato..

The Penn Stsate researchers note that the identification of at least one repellent compound raises the possibility of eventually using airborne chemicals to deter plant parasites. Looking forward, they would also like to determine exactly how the parasites are able to sense and respond to host volatiles. They hope to identify the specific chemical receptors involved. They are also examining the defensive mechanisms by which host plants respond to attack by parasitic plants.
-end-


Penn State

Related Parasites Articles from Brightsurf:

When malaria parasites trick liver cells to let themselves in
A new study led by Maria Manuel Mota, group leader at Instituto de Medicina Molecular, now shows that malaria parasites secrete the protein EXP2 that is required for their entry into hepatocytes.

How deadly parasites 'glide' into human cells
A group of scientists led by EMBL Hamburg's Christian Löw provide insights into the molecular structure of proteins involved in the gliding movements through which the parasites causing malaria and toxoplasmosis invade human cells.

How malaria parasites withstand a fever's heat
The parasites that cause 200 million cases of malaria each year can withstand feverish temperatures that make their human hosts miserable.

New studies show how to save parasites and why it's important
An international group of scientists published a paper, Aug. 1, 2020, in a special edition of the journal Biological Conservation that lays out an ambitious global conservation plan for parasites.

More flowers and pollinator diversity could help protect bees from parasites
Having more flowers and maintaining diverse bee communities could help reduce the spread of bee parasites, according to a new study.

How Toxoplasma parasites glide so swiftly (video)
If you're a cat owner, you might have heard of Toxoplasma gondii, a protozoan that sometimes infects humans through contact with contaminated feces in litterboxes.

Parasites and the microbiome
In a study of ethnically diverse people from Cameroon, the presence of a parasite infection was closely linked to the make-up of the gastrointestinal microbiome, according to a research team led by Penn scientists.

Clocking in with malaria parasites
Discovery of a malaria parasite's internal clock could lead to new treatment strategies.

Feeding bluebirds helps fend off parasites
If you feed the birds in your backyard, you may be doing more than just making sure they have a source of food: you may be helping baby birds give parasites the boot.

Scientists discover how malaria parasites import sugar
Researchers at Stockholm University has established how sugar is taken up by the malaria parasite, a discovery with the potential to improve the development of antimalarial drugs.

Read More: Parasites News and Parasites 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.