The Basic Science Research Concept

“So are you trying to make plants more defended?”

This is often the first question I encounter when I share my research questions with anyone that does not spend their work life thinking about plants. Before the conversation can get much further, I find it helps to introduce the difference between basic science research and applied research.

Both are important, but it is easier for people to connect with applied research: research designed to improve the way humans live. However, many of the solutions we use today came as a result of discoveries from basic science research: research designed to understand the way something works for the sake of understanding.

Like what?

PCR: the technology that lets us duplicate tiny amounts of DNA, was only possible because a scientist was curious about how acidic and hot Yellowstone hot springs could be for bacteria to survive. Bacteria flourishing at high temperatures have DNA too, and the enzymes that could replicate DNA despite the heat were eventually extracted and were able to withstand the hot temperatures in PCR.

Efficient building design: scientists were curious about the structure of termite mounds, which can maintain a constant temperature despite the heat of the desert. The results from these studies were used to construct a building in Zimbabwe (The Eastgate Centre) that uses 90% less energy.

Velcro, the ubiquitous adhesive found on light-up shoes, was inspired by plant hook-shaped hairs.

And the list goes on. The moral of the story is that technology gets along well with natural selection, but first we have to understand how it all works.

My research goal is to understand how plant-insect interactions change as a result of the chemistry within the plants that have a symbiotic relationship with nitrogen-fixing bacteria. I spend my time at my desk wondering about how and when plants will use their resources to make the stuff that protect them- either directly by making poisonous chemicals, or indirectly, by sending volatile compounds into the air to communicate with the predators of their attackers.

Instead of trying to get plants to do anything, my goal is to understand what they actually do on their own- to understand the unknown aspects of their biology.

Do these bacteria play an important role in the food web by altering plant-insect interactions? My research will let you know.

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Plants with Benefits

Maintaining relationships, even great ones, can be challenging.

Some plants juggle multiple relationships ALL of the time.

Think of an organism that does something helpful for a plant. Bees, hummingbirds, and other pollinators may come to mind. But plants also recruit toucans, black bears, and other seed dispersers as well as predatory insects such as ants and wasps for defense.

And then there are microbes.

My goal for this research paper was to show how one microbe in particular, nitrogen-fixing bacteria called rhizobia, can alter a plants’ entire network of relationships—from the bottom-up.

Rhizobia live inside nodules on plant roots in a tight-knit symbiotic relationship, exchanging fertilizer for sugars from photosynthesis. Plants that form this relationship benefit immensely from the nitrogen, but providing sugar in return can tax the plant.


Plants also use their homemade sugar to secrete extrafloral nectar. Nectar typically attracts pollinators, but in the case of extrafloral nectar, plants produce nectar to attract ants, which patrol their sugar source like bodyguards. By evicting intruding bugs attempting to feed on the host plant, extrafloral nectar can be an effective indirect plant defense…

…as long as the ants show up to do their part.


But the key result from our paper is that ants are less attracted to plants that have nitrogen-fixing rhizobia in root nodules belowground. Keep in mind- the ants and bacteria do not interact directly. What connects ant to bacteria?

The plant between them.

Plant chemistry changes when plants form symbiosis with rhizobia. Plants with nitrogen-fixers make more of the nitrogen-based traits, protein and cyanogenesis. Surprise. But these plants also secrete less sugary nectar, therefore attracting fewer ants.

Even in the plant world, some relationships can be more demanding than others.

How do rhizobia cause plants to compromise their ant relationships?

It could be that rhizobia demand so much sugar to keep the nitrogen flowing that the plant’s excess sugar supply is exhausted, leaving little to serve as ant lures. Alternatively, why would plants that get a constant supply of nitrogen to make cyanide need to attract ants anyways?

Either way, we now know rhizobia can change plant relationships with ants.

But why would that matter?
Ants are everywhere- so are rhizobia. Both play important roles in how ecosystems function, but the fact that they can indirectly affect one another may have strong and widely overlooked impacts on plant ecology.

© Adrienne Godschalx (adrg@pdx.edu) August 19, 2015

The Crazy Things Plants do for Nitrogen

What’s the big deal with nitrogen, you ask? Nitrogen is the key ingredient in proteins. In biology, if our DNA does the talkin’, proteins do the walkin’. Proteins can be enzymes that help reactions happen. In plants, the sugar-making part of photosynthesis, (aka the dark cycle) is run by an enzyme called RuBisCO, which also happens to be the most abundant enzyme on earth. The remarkable thing about this super important enzyme, responsible for turning CO2 into sugars, is that it is a super slow, clunky enzyme. Plants often compensate for its slowness by making more of it. More enzyme=more protein. Plants need nitrogen to make proteins.

I thought about naming this post: “Nodules, photosynthetic pathways, and carnivorous plants, oh my!” But the number of syllables got in my way. Still, these three evolutionary wonders all help plants deal with limited nitrogen, and deserve to show up in a blog post together.

But why are plants so nitrogen-limited in nature?

The answer includes a terrifying word from Intro to Chemistry: stoichiometry. (Which I recently learned from this fantastic paper: Nitrogen and Nature.)

The number of nitrogen molecules in plants is small among all of the carbon molecules, which drives the ratio of carbon to nitrogen molecules the leaf litter, overwhelming the soil with carbon and making nitrogen hard to come by. Further, nitrogen is typically stuck directly to carbon in a covalent bond, which is harder to break off than ionic bonds that work like magnets. Even when nitrogen is in this “magnetic” form, these ions are negatively charged—just like soil particles—and easily leech from the soil with rainwater.

Yes, that is why nitrogen is limited in the soil, but most of the nitrogen in the world is in the air; isn’t there plenty of it in the air that plants could use? The atmosphere is made up of roughly 79% nitrogen. Unfortunately, that nitrogen is not accessible to plants. Each nitrogen is tightly bound to a second nitrogen atom like this: N≡N, and triple bonds are especially tough to break, even for a plant.

But some bacteria can break all three bonds!! Microbes have crazy metabolic pathways, many of which are crucial to the chemical balance of the world existing as we know it. By turning N≡N into fertilizer in a process called nitrogen fixation, the nitrogen cycle is driven by microbes.

Evolutionary wonder #1: Some plants figured this out (over evolutionary time), and formed a symbiotic relationship with nitrogen-fixing bacteria. These groups of bacteria: rhizobia, Frankia, and cyanobacteria, live in nodules on their plant hosts’ roots and provide a source of house-made fertilizer in exchange for sugars. Plants, which do photosynthesis, that have nitrogen-fixing bacteria in their roots represent the interface of two important geochemical cycles: the nitrogen and carbon cycles.

Not only are plants solar-powered sugar factories, but some plants can make sugars through several different metabolic pathways: C3, C4, and CAM. For perspective- we don’t even have one carbon assimilating pathway, but the plant kingdom has three.

Evolutionary Wonder #2: In “normal photosynthesis”, or C3 photosynthesis, plants lose water through pores called stomata when they take in carbon to turn into sugars. Some plants reduce the amount of water they lose by either opening their stomata at night when the air is cooler (Crassulacean Acid Metabolism or CAM), or by concentrating the CO2 in a separate compartment with those super slow enzymes (C4). Why are these nitrogen-limited adaptations? Because making enzymes more efficient helps plants with the initial problem of needing nitrogen to churn out tons of slow, clunky enzymes.

Yet some plants carry out old fashioned C3 photosynthesis without any N-fixing bacteria in root nodules and are able to live in extremely nitrogen-poor soil. Their secret? Eat the tiny packets of nitrogen buzzing and crawling everywhere around them.

Evolutionary wonder #3: Carnivorous plants are exciting because they deviate from our basic understanding of what plants do. When my mom let me buy a $4.99 Venus fly trap at City Market, my mind was blown. I wrote songs and recorded one too many home videos about the plant that eats flies!

Even Darwin himself was excited by this menacing behavior and laid some groundwork for research on how Venus flytraps close in on their prey.

Despite the diversity of strategy, ranging from pitcher plants that collect bugs that slip into the plants’ digestive juices to sticky plants that catch bugs with glandular hairs, carnivorous plants evolved to deal with stressful environments lacking that not-so-secret ingredient in all proteins:

Nitrogen.