If we want to dismiss something as irrelevant, we'd say that it's "as boring as watching the grass grow." And yet grasses—including corn, wheat and rice—make up most of the plant-based calories humans eat, as well as most of the calories fed to livestock. Perhaps we should have been paying attention to such an important plant, because we now know, thanks to new research led by biologists at the University of Massachusetts Amherst and published in Current Biology, that grasses grow according to temperature—not light, like other plants.
Scientists have known for ages that many plants respond to light cues, which trigger their growth cycles. All plants grow fastest at specific times during the day and during specific periods of the year, and most of them respond to seasonal and daily changes in light levels.
But grasses are different.
"All the things we thought we knew about the timing of daily growth rhythms in plants turn out to be different in the plants that provide almost all of our calories and most of the calories that we feed to the animals we eat," says Samuel Hazen, professor of biology at UMass Amherst and the paper's senior author.
Grasses don't seem to respond to light at all. In fact, they respond only to temperature.
"It's easy enough to see this," says Hazen, who previously led a team showing that temperature alone governs how leaves of grass grow. It turns out that each leaf's cells divide and elongate when the temperature is right, making the leaf longer.
But what about grasses' woody stems? It is, after all, those stems that allow wheat, corn and rice to grow tall, where they can be more easily harvested. The rigidity of their stems is provided by a thickening of the secondary walls around cells in the stem. The problem for scientists is that this growth happens on a microscopic scale, and researchers have had no way to watch it unfold in real time.
"This is where my very talented graduate student, first author Greg Gregory, and co-author Dave Follette, director of advanced digital design and fabrication and device characterization at UMass Amherst's Institute for Applied Life Sciences, come in," says Hazen.
Gregory and Follette designed a custom real-time bioluminescence imaging system that could take dozens of time-lapse pictures of a model grass, called purple false brome, as it grew under various conditions. But this purple false brome was different. The team engineered the plants with a genetic reporter that linked CESA8, a key gene involved in building the rigid secondary walls, to firefly luciferase—the enzyme that makes fireflies glow. Whenever the CESA8 gene was expressed, the cells emitted a faint glow that the imaging system could detect.
"For the first time, we are now able to watch a gene responsible for building the plant's structural support turn on and literally glow inside a living stem," Gregory says. "By making this process visible, we can now finally uncover how the grass responds to the environment in regard to building secondary cell walls."
The team then tested a variety of light and temperature conditions to figure out how each variable influenced a plant's growth and found that temperature alone drives the growth rhythm of grass stems—but not in the way the team expected.
In general, the grass grew faster during cool nights and slower during warm days, but it grew fastest of all when there were warm pulses throughout the cool night and slowest when there were cool pulses during the warm day. Cold temperatures initially suppressed cell-wall thickening, but prolonged periods of cold promoted it. Meanwhile, the inverse was true for warmer temperatures.
This "incoherent feed-forward loop," modeled for the biologists by their mathematician co-author, Didier Gonze from Belgium's Université Libre de Bruxelles, means that temperature both activates grass growth while also setting up a delayed response to turn the growth off.
So what does this mean in a world where nighttime temperatures are rising due to global climate change?
Though the research doesn't yet address these sorts of applied questions, any future work in this direction will rely on Hazen and his colleagues' foundational research into the mysteries of how grasses grow.
Publication details
Greg A. Gregory et al, Temperature signals drive grass secondary cell wall thickening, Current Biology (2026). DOI: 10.1016/j.cub.2026.06.034
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Citation: Grasses provide most of the world's calories—but we're only now starting to learn how they grow (2026, July 11) retrieved 11 July 2026 from https://phys.org/news/2026-07-grasses-world-calories.html
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