Parasitic Plants Offer Insight Into Plant Communication

dodder

You might be familiar with carnivorous plants (like the Venus fly trap) that feed on insects, but have you heard of parasitic plants that feed on other plants?

Parasitic plants aren’t much of a problem for home gardeners in Virginia, but they do have very important lessons to teach us about the ways that plants communicate with and sense one another. For example, dodder, a relatively common parasitic plant in Virginia, germinates and then grows towards a host plant that it will latch onto in order to steal water and nutrients. Dodder has evolved a sophisticated set of sensory adaptations that allow it to find appropriate host plants without being able to “see” what’s around it.

According to Dr. Jim Westwood, professor of PPWS and an expert on dodder and parasitic plants, dodder seedlings sense the location of potential host plants by recognizing chemical vapors emitted by the plants around them and, potentially, by recognizing the color of surrounding material, for example identifying a green stem among brown, non-plant materials.

Parasitic plants in the family Orobanche provide another amazing example of adaptation to their surroundings. Orobanche seeds will not germinate until an appropriate host plant is nearby. Seeds may lie dormant in the soil for many years until stimulated to germinate by compounds emitted by the nearby roots of a suitable host. After germination, Orobanche seedlings attach to the roots of this host in order to steal water and nutrients.

Orobanche elatior

Orobanche elatior

Like Orobanche plants, dodder is deficient in chlorophyll and must latch onto a host plant for water and nutrients. However, Dr. Westwood’s recent research shows that dodder shares even more with its host than previously thought.

“Dodder has open connections with the host plant. They fuse so well it’s like a seamless graft,” says Dr. Westwood. “They exchange lots of molecules, including microRNA–which people used to think didn’t even leave the cell.”

What is microRNA?

DNA is the set of genetic instructions, common to every cell in an organism, that directs growth and development. MicroRNA helps regulate which parts of DNA are silenced or expressed in a particular cell, for example allowing for the formation of different types of cells (e.g. bone or blood cells) within an organism.

An example of dodder from: https://oak.ppws.vt.edu/~flessner/weedguide/cvcca.htm

In addition to dodder, gardeners and plant lovers in Virginia might encounter a few other parasitic plants. Different types of mistletoe (the common name for many different species of parasitic plants) grow on a variety of host trees in Virginia. Conopholis americana (also known as squaw root or cancer root) is also common in the Virginia mountains.

“If you hike in the woods in the mountains you can find Conopholis americana growing under oak trees. It has a small cream-to-brown flower and it doesn’t do damage to the oak trees it grows on,” says Dr. Westwood.

squaw root

Conopholis americana from: https://oak.ppws.vt.edu/~flessner/weedguide/conam.htm

While it might appear as if all the plants in an ecosystem–or your home garden–exist independently from one another, these highly adapted parasitic plants illustrate that plants are more aware of their surroundings than you might think.

Next time you’re out for a hike or examining the weeds in your home landscape, check for Conopholis americana or dodder and think of the many scientific insights about our world that these highly adapted plants can offer.

For more information on dodder, see Dr. Westwood’s research page: https://www.ppws.vt.edu/research/westwood-lab.html

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