What makes plants tick: Figuring out how to thrive

This sugar snap pea tendril is exhibiting thigmotropism, grasping for support in order to climb.

Pete is a sugar snap pea and the smartest vegetable in our garden. While all the vegetables just sit there, Pete learned how to grab a stake and grow to the top.

In some parts of botanical academia, there are debates about plant intelligence. To the horror of some vegetarians, Peter Tompkins released "The Secret Life of Plants" in 1973 and claimed that plants could feel pain, citing plants hooked up to a polygraph machine experienced an electrical impulse when another plant was stomped to death in front of them.

The controversial claims, however, could not be replicated by other scientists.

It seems that the definition of intelligence is what's at stake. Most scientists regard plant behavior as adaptive reactions instead of conscious decision-making. Plants evolved much differently than animals because they are stationary. Being rooted in the ground, it's not beneficial to have a brain that monitors all activities. Plants can lose more than 90 percent of their mass and survive.

But plants are much more complex than just organisms reaching for sun and water. Our yards are, in many ways, botanical battlegrounds where space and resources are highly coveted, not too different from humans.

Some research has demonstrated that the sound of insect chewing can cause nearby plants to deploy defensive measures, such as toxin production, taste alteration or textural changes.

In some cases, a plant under attack may release compounds that attract beneficial insects, like calling the cavalry.

Botanical chemical warfare, called allelopathy, is often employed where roots release growth hormones to negatively affect competitors.

There are also plant alliances.

Research by Suzanne Simard, University of British Columbia, introduced radioactive carbon isotopes to a single tree in a forest. A few days later, she followed the isotopes' presence with a Geiger counter and discovered it in surrounding trees of the same species, likely traveling through a vast network of beneficial fungi that connects roots. In fact, greater amounts were found in smaller trees, as if aiding their growth.

Obviously, plants grow too slow for us to witness. However, speeded up on a recording and it will look like Pete, our sugar snap pea, is searching for something to climb. Plants achieve these seemingly intelligent reactions by means of tropisms: growth responses to stimuli.

Phototropism is a response to light. Leaves and stems grow toward light, which means more photosynthesis. Roots, on the other hand, grow away from light. Rather than a nervous system to guide them, plants utilize growth hormones called auxins. Sunlight inhibits auxin production, thus limiting elongation in cells exposed to light. The cells on the shady side of the stem, however, are not affected and auxin production results in faster growth that bends the stem toward the light.

Heliotropism is slightly different than phototropism. Have you ever noticed sunflowers tracking the sun throughout the day? They operate like solar panels, increasing their energy production by always facing the sun. They do this by turning, not growing, toward light by means of specialized motor cells that alter turgor pressure.

Roots grow into soil where water and nutrients are found. While root tropisms are complex, geotropism, also called gravitropism, is the effect of gravity. Shoots grow away from gravity and roots toward it. They do this by means of specialized plant cells that contain dense elements more affected by gravity than the surrounding cellular environment. Lacking gravity in space experiments, shoots and roots will initially grow in all directions but eventually other tropisms kick in and normal growth resumes.

Finally, Pete, our sugar snap pea, isn't really smart. He uses thigmotropism, a reaction to physical contact. Auxin production is limited in cells that make contact with an object. However, the cells on the stem opposite of the contact continue to grow and, thus, wrap around the support. The competitive advantage Pete and all vines have are that fewer resources are needed for support. They don't need a solid trunk; they can focus on growing fast.

Just ask the vine everyone in the South knows.

His name is kudzu.

Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at tony.bertauski@tridenttech.edu.