From flower to fruit: the struggle within

By Julie Gazaille Sep 9th, 2026

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In 5 seconds UdeM scientists reveal how a tug-of-war between fast- and slow-growing tissues sculpts fruit in a flowering plant.

Arabidopsis thaliana, or thale cress, is a small plant biologists have used as a reference model for decades.
Photo : Getty

Unlike an animal cell, a plant cell can't crawl or migrate. It's locked inside a rigid wall, cemented to its neighbours for life. A cell born at the centre of a young fruit will still be there when that fruit ripens.

That constraint has a direct consequence. When two tissues are fused together but programmed to grow at different speeds, neither can simply pull away, and something has to give.

The faster tissue puts the slower one under tension; the slower one, in turn, holds the faster one back.

A study by scientists at Université de Montréal shows that this tug-of-war, far from being a mere inconvenience, is one of the tools the plant uses to build its fruit.

PhD student Binghan Wang led the project, supervised by Daniel Kierzkowski, a professor in UdeM's Department of Biological Sciences and a researcher at the Institute for Research in Plant Biology (IRBV).

The study combines time-lapse imaging, microsurgery, genetics and computer modelling, the latter developed with Richard Smith of the John Innes Centre in the U.K.

Thale cress under the microscope

The team studied Arabidopsis thaliana, or thale cress, a small plant biologists have used as a reference model for decades.

It has a short life cycle, a fully sequenced and well-understood genome, and a broad genetic toolkit that makes it easy to create mutants to test a hypothesis.

What's discovered in thale cress usually sheds light on mechanisms shared by many other plants, such as those in the Brassicaceae family, which includes canola, cabbage, broccoli and others.

Daniel Kierzkowski, professor in the Department of Biological Sciences at Université de Montréal
Photo : Amélie Philibert, Université de Montréal

Two tissues, one organ

The researchers focused on the gynoecium, the flower's female reproductive organ, the structure that becomes the fruit once fertilized, and where ovules (which become seeds) form.

The gynoecium is made of two very different tissues, fused together:

the valves, on the sides of the organ, which grow fast (about four times faster than the tissue next to them);
and the replum, a narrow central band that grows slowly, but almost entirely in one direction.

That slowness is no accident: the replum is connected to the meristem, a small reservoir of actively dividing cells that produces the ovules.

In every plant, meristems grow slowly, a property considered essential to building organs reliably.

A developing flower in thale cress
Photo : Silvia Silveira

Stretched into shape

What happens when a slow band is wedged between two fast-growing tissues? The valves stretch the replum, making it longer than it could ever become on its own.

The clearest proof came from the simplest experiment: when researchers surgically removed a single valve, the organ consistently curved toward the replum, exposing the imbalance in pull.

The reverse holds, too. In the fruitfull mutant, a plant in which a gene needed for normal valve growth has been switched off, the replum becomes short and wide, and the plant produces fewer ovules.

Ovules, it turns out, don't all appear at once: as the tissue that carries them lengthens, new gaps open up to hold more of them. Stretching the replum, in other words, makes room for more seeds.

"The valves look like the passive part of the story, but they're actually the lever," said Kierzkowski.

“If you wanted to change how many seeds a fruit can hold, our results suggest you'd need to target valve growth early in development.”

Trapped, the tissue wrinkles

Here's the surprising part: pulling on the replum doesn't make it grow faster. It changes the direction of its growth instead.

In the fruitfull mutant, where the valves stop growing altogether after fertilization, the replum keeps lengthening anyway, with nowhere to go. Trapped, it wrinkles, the way a long strip of fabric puckers when it's sewn onto a shorter piece. As those folds pile up, the swollen replum physically pushes the two now-inert valves apart.

"What we find beautiful here is that the plant never loses its mechanical continuity — there's no rupture in the tissue," Kierzkowski noted. "When the tissue is under heavy compression, it folds in on itself, and it still holds together."

Microscopy, microsurgery and more

To track growth cell by cell, the researchers used time-lapse confocal microscopy, a technique that enables imaging of cells on the surface of an organ without damaging it.

By repeating these shots at regular intervals over eight days, the team could precisely measure the speed and direction of growth of every cell in the gynoecium - the very colours visible in the images.

That direct observation was then confirmed through microsurgery (removing valves), genetics (the fruitfull mutant) and a computer model developed with Smith.

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