The world is a rough place to grow up. Just ask a stinging nettle. Credit: Ashley Braun/All rights reserved.
Life as a plant can be stressful. Once, or rather, if, you sprout where you’re planted, you’re faced with some immediate limitations. Let’s hope you have just the right exposure to sunlight, water, and nutrients. Maybe not too much wind or competition for space. And watch out for herbivores.
But that’s about all plants can do, right? Just watch.
While plants do have some obvious defenses (thorns, toxins, tannins, and the like), we humans often think of plants as being passive. We don’t give them much credit for taking a stand against the world. “Vegging out” means sitting around doing nothing, unaware and unresponsive. Yet researchers are finding many examples of plants actively responding to the world around them and in a variety of ways.
Yo, Romeo: Smell Ya Later
I forgot to mention that gall fly larvae spit causes huge galls (ball-shaped masses) to form on the goldenrod’s stem. They then live inside the gall all winter, sucking nutrients out of the plant from the inside. No wonder the plant is pissed. Credit: Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor/Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.
Take smelling, for example. In 2012, entomologists at The Pennsylvania State University documented both in the field and in the lab evidence of a plant that, when exposed to the smelly male sex hormones of a long-time enemy, is able to beef up its chemical defenses against it.
It seems that once the tall goldenrod plant, Solidago altissima, gets a whiff of a romantically inclined male goldenrod gall fly, Eurosta solidagini, it begins releasing the defense hormone, jasmonic acid, which is a real turn-off to lady flies. Particularly, as it turns out, when they’re looking for a place to lay their eggs, which hatch into hungry little caterpillars and only have a stomach for tall goldenrod.
Male flies release clouds of this pheromone “perfume” when they’re in the mood for love, sitting on the leaves of a tall goldenrod plant and waiting to attract a female. After they mate, the female flits away to find a suitable nursery plant for her bug babies. In this search, she goes from plant to plant, sticking her egg-laying organs into goldenrod buds and getting a “taste” for the plant with her feet and ovipositor. If she likes the taste, she lays her eggs. If not, on to the next plant.
However, once a plant is exposed to the male flies’ odor, not only are they less likely to have female flies inject their eggs into them, but to a large extent they also avoid being eaten by other hungry insects. Jasmonic acid must taste terrible to a would-be mother goldenrod gall fly. But the musk of a male fly apparently smells like heaven to a nervous goldenrod.
Beating the Heat
Another very real concern for plants is heat stress, which is only going to get worse as the global climate warms. The United Nations Intergovernmental Panel on Climate Change is in the process of releasing its latest series of reports on global warming and its impacts on the natural and human worlds. A part of one of their reports was leaked before being published, but it apparently has dire warnings for agriculture.
According to the New York Times:
In a departure from an earlier assessment, the scientists concluded that rising temperatures will have some beneficial effects on crops in some places, but that globally they will make it harder for crops to thrive—perhaps reducing production over all by as much as 2 percent each decade for the rest of this century, compared with what it would be without climate change.
And, the scientists say, they are already seeing the harmful effects in some regions.
Heat waves have already taken a toll on crop production in recent years (see Europe in 2003). A growing body of research suggests that important crops such as corn and soybeans are more sensitive to extreme heat than previously thought.
What does “extreme heat” mean? The mid-80s. Having grown up with sticky Midwestern summers, that doesn’t even sound that hot, but it translates to a sudden drop in production for these plants.
Even so, plants do have ways to cope with heat stress. Researchers at Iowa State University have recently uncovered some of the molecular pathways that plants use to deal with stress. From a press release:
The research takes a close look at what happens to the model plant Arabidopsis at a molecular level when faced with environmental stress. It involves a process called unfolded protein response, which can act as an alarm system when the plant senses harsh conditions. When the alarm goes off, the plant activates survival measures that can protect crops from succumbing to weather extremes.
Considering the warming world facing plants, they’re going to need these kind of defenses to stay alive. And why should we expect them to just sit back and watch?