Caffeine: What’s in it for the coffee plant?
By R. Gary Raham
Ah…that first cup of coffee each day! It almost seems like just the smell of those alkaloids and flavonoids from roasting coffee beans could lift us out of bed in the morning. And that first sip—shared by 26,000 other coffee lovers every second—provides that jolt of caffeine that finally shatters the brittle remnants of last night’s dreams. We owe this pleasurable largesse to the diligent efforts of coffee plants that expend time and energy to transform a precursor compound (xanthosine) into the psychoactive chemical we love and depend upon. Why do those coffee plants do it?
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What’s in it for them?
This is the kind of question biologists ask all the time, because when plants or animals expend energy to do something that means it’s important for their survival. An international team of scientists published an article in the journal Science in 2014 that hints at some answers to the question. Their research involved analyzing the genome of Coffea canephora, one of the three main commercial species of coffee plant, and comparing it with the genomes of other caffeine producing plants like those used to make tea, cocoa (processed cacao beans), and chocolate. (See http://coffee-genome.org/coffeacanephora)
One key discovery was that plants find caffeine so useful that they have evolved more than one way to make it. Coffee plants and cacao plants, for example—as revealed in their genomes—found different paths to making the same compound. And the biochemical enzymes involved in caffeine production, the N-methyltransferases, also participate in creating a variety of compounds we find useful, like the salicylic acid found in willow bark that is the pharmaceutical basis of one of the first wonder drugs, aspirin.
But again: what’s in it for the coffee plants? The simple answer is they use it to control animal behavior.
Caffeine is toxic in high quantities for both plants and animals. When coffee plant leaves fall to the ground and decay they create killing fields laced with caffeine that discourages the seed germination of plant competitors. The caffeine in coffee plant leaves also discourages foraging by hungry insects. Many insects have evolved caffeine-detecting receptors that divert them to less toxic meals.
But in lower doses, caffeine creates a buzz that other insects find as stimulating as we do. Scientists have found that caffeine-spiked nectar improves the memory of insects. They will remember and return to those flowers providing a caffeine high, and thus spread the pollen of those plants far and wide. Since plants can’t walk or drive to some exciting tryst in a neighboring field, the insects serve as their romantic liaisons. Blogger Carl Zimmer in his New York Times article “How Caffeine Evolved to Help Plants Survive and Help People Wake Up” quotes neurobiologist Julie A. Mustard: “It’s a very cool fact that you can use one molecule to do a negative thing and a positive one.”
Johns Hopkins researchers have also reported that caffeine boosts human long-term memory (http://hub.jhu.edu/2014/01/12/caffeine-enhances-memory). Specifically, they found that a 200-milligram caffeine tablet significantly improved recognition of images from one day to the next. As it turns out, 200 milligrams is the average daily intake of caffeine for those of us who imbibe the stuff—which is 80% of adults in the U.S., according to the USDA. The same agency reported that 90% of people worldwide consume caffeine in one form or another.
So, as you sit in the kitchen or at the coffee shop with that cup of joe—one of 2.25 billion cups consumed every day—consider this: Those coffee plants out there have Homo sapiens cultivating over 27 million acres of land on their behalf. They seem to have us right where they want us: raising their seedlings and spreading them far and wide.
It’s enough to make a guy want to call in a lawyer to renegotiate the arrangement. One just has to be sure not to disturb the legal staff until they get that first cup of coffee under their belt in the morning.