How does a leaf know when to stop growing? Plant biologists have measured growth in countless separate experiments, but the data were gathered in such different ways that comparing them was nearly impossible. Viraj Alimchandani, a PhD student supervised by Anne-Lise Routier-Kierzkowska, Canada Research Chair holder at Université de Montréal's Institut de recherche en biologie végétale, combined results from 176 experiments on the model plant Arabidopsis thaliana into a shared framework, publishing the first atlas of plant growth in New Phytologist.
The atlas overturns some textbook assumptions. Roots, it shows, grow mainly through cell stretching and specialisation in the elongation zone rather than through cell division in the meristem, as commonly supposed. Leaves and young stems both pass through rapid early growth before settling into steadier expansion, and in the meristem, cell expansion follows a conserved offset between central and peripheral zones, hinting at deep regularities in how plants build themselves.
Most consequentially, final organ size emerges from a trade-off between growth rate and how long the scaling phase lasts, a principle the team tested by comparing dark- and light-grown seedlings and leaves of different ages. Events in the earliest stages of growth leave a lasting imprint on final size, which means early measurements matter. As a common reference point, the atlas should help researchers interpret mutant phenotypes, design experiments and connect genes to the growth patterns they shape.