What makes plants grow to a certain size? From the tiniest cells to whole leaves, roots, and stems, growth has to be carefully coordinated – but until now, it has been hard to compare findings from different studies.
In a new study, researchers at Université de Montréal combined results from 176 experiments on Arabidopsis thaliana, a popular model organism in plant biology and genetics, to build the first ever atlas of plant growth.
The study is published today in New Phytologist.
"By creating a common framework, we were able to bring together data collected in many different ways, making it possible to directly compare growth across organs and scales," said Viraj Alimchandani, a PhD student supervised by UdeM biophysics professor Anne-Lise Routier-Kierzkowska.
In their lab at UdeM's Institut de recherche en biologie végétale, the scientists found that plants use both organ-specific and shared strategies to control their size.
"For example, roots grow mainly through the stretching and specialisation of cells in a particular region, while leaves and stems show surprisingly similar patterns of rapid early growth followed by steadier expansion as they mature," said Alimchandani.
"Crucially, we discovered that what happens during the earliest stages of growth can have a lasting effect on the final size of an organ, everything from shoots to roots to leaves," he said.
Both organ-specific and general growth strategies are linked to size control in the plants studied, the scientists found. In the meristem, for instance, there was a conserved offset in cell expansion between central and peripheral zones.
Elongation in the roots, for their part, was driven mainly by cell expansion and differentiation in the elongation zone, rather than by cell dynamics in the meristem as commonly expected. Hypocotyl and leaf growth showed unexpected parallels: early exponential elongation resembled primary morphogenesis, while later linear growth matched secondary morphogenesis.
Comparing dark-grown versus light-grown hypocotyls, and juvenile versus transition leaves, showed that organ size was modulated by a trade-off between growth rate and duration of the scaling phase. Cellular-scale growth during early development was shown to influence final organ size, underscoring the need for early-stage measurements.
The growth atlas offers a new reference point for plant research in general, he added, a framework for interpreting mutant phenotypes, guiding how experiments are conceived, and advancing scientists' understanding of growth regulation across plant organs.
"It will help scientists understand how genes affect growth, improve experimental design and, in the long run, shed light on how plants adapt and thrive," said Routier-Kierzkowska, an associate professor and Canada Research Chair whose lab specializes in investigating the biophysics of cells.
