Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

Weed Power

Sunday, May 12, 2013

It has been said that knowledge is power. If that is true, then the Mouse Eared Cress must be the most powerful plant in the world.

What’s that you say? You never heard of the mouse eared cress? Not surprising. And don’t bother to look it up in your Peterson’s Field Guide to Wildflowers. It’s not there. You see, the mouse eared cress makes its living by being inconspicuous.

The mouse eared cress, known scientifically as Arabidopsis thaliana is an invasive. It is widespread in Europe and presumably came to this country a few hundred years ago, although there is no record of when, where or how it first arrived. Once it arrived, however, it was able to spread quickly. The seeds are tiny – barely visible to the naked eye - and easily transported by sticking to birds and insects. Once the seeds are dropped in a suitable location, the plant can go about its business making more seeds – thousands per plant.

Everything about the mouse eared cress seems designed to make you overlook it. The adult plant is small. In full flower, it stands about 4 inches tall. It has a rosette of leaves that hug the ground. The flowers are white, but too small to really notice. And don’t look for insects pollinating this flower. The plant usually pollinates itself.
Even though it is an invasive, mouse eared cress is not likely to take over an area like other invasives. In fact, it avoids competition. It grows in disturbed waste areas. But it disappears as soon as other plants move in. Therefore, it must do its business quickly. The full life cycle of the plant, from the time a seed grows into a plant and produces new seeds, takes a mere six weeks, a very short lifespan.

Here in New England, the mouse eared cress seeds usually germinate in the spring and these plants are done flowering and have disappeared completely before the summer. The seeds from these plants won’t germinate until next spring. They can’t hatch until they have gone through the cold of a winter.
In milder climates, and occasionally here in New England, the seeds hatch in the fall and the plant will grow its rosette of basal leaves. Then the plant becomes dormant for the winter. This fall growth gives the plant a head start for the next spring. When warm weather arrives, the plant grows flowers and produces the seeds that will germinate in the fall.

How is it that such a small inconspicuous plant is so powerful? While it is virtually unknown to most naturalists, it is quite famous among scientists, especially plant biologists. You see, Arabidopsis thaliana is a model organism, an organism that scientists use to study how biology works. In the animal world, both the house mouse and the fruit fly are model organisms. In the plant world, it is Arabidopsis. If many scientists study different aspects about one plant and pool their knowledge, a lot can be learned in a very short period of time. That is what has been happening with this little weed.
Since scientists need to grow many plants to do their experiments, it is easy to see why Arabidopsis is a good choice for a model organism. Compare this plant to another, more familiar plant – Quercus alba, the white oak. A scientist can plant the seeds of Arabidopsis and six weeks later, the plants are producing new seeds. The white oak takes at least twenty years to produce seeds. That’s a long time for a biologist to wait.
To get reliable results, a scientist must repeat an experiment many times, so a lot of plants are needed. A thousand Arabidopsis plants can be grown on a six foot light table. It would take a forest to grow a thousand white oaks. Clearly, Arabidopsis is a much more suitable model organism than an oak tree.

So what sort of things are scientists learning from their study of Arabidopsis? Geneticists, scientists who study genes, were the first group to study the plant. Genes, as you may remember from high school biology, are the bodys' chemical instructions telling the cells what chemicals to make, when to make them and where to put them. In other words, you are what you are in large part because of your genes. Us humans have about 30,000 genes. When you consider how complex humans are and how simple Arabidopsis is, you may be surprised to hear that Arabidopsis has about 32,000 genes, 2,000 more than we humans. Not bad for an insignificant little plant.
Once all 32,000 genes were identified, scientists could begin to figure out what they do and how they do it. Then they could begin to answer some basic questions about plant biology. Many of these questions most people never even think about. It is just taken for granted that plants do these things. But biologists want to know the answers. Here are some of the basic biology questions that Arabidopsis is helping to answer:

When a seed sprouts, how does it know when it is above the ground and should start to make leaves? Leaves that formed underground would not do the plant any good.

Sunlight is a mix of all the colors of the rainbow. Do plant use all of the light or just certain colors?

Do plants make any chemicals that protect them from insect damage?

Sugar is the source of energy for most living things. Plants make sugar through photosynthesis. Animals get their sugar from their environment – from the food they eat. Can plants utilize sugar from their environment – like animals?

These are just a few of many of the basic questions that scientists are asking. The knowledge we get from Arabidopsis helps scientists figure out how life works. But it can also help us answer more mundane questions. For instance, How deep should you plant your seeds? What color light should you provide your house plants? What chemicals might be effective in protecting plants from insect damage? If you dissolve some sugar in the water you use to water your plants, will they grow better?

If size and stature is any indication, the mouse eared cress is a pretty insignificant little weed. But if power is in fact measured by knowledge , then Arabidopsis is one of our most important plants. But just try to find it.