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Throughout their growth cycle, plants sprout all kinds of intricate and complex structures that range from scarcely apparent to invisible in the seedling stage. Leaves, flowers and seeds can appear, seemingly out of nowhere, from a smooth stem or branch. But the details of how cellular development occurs—why one cell might give rise to petal cells and another to bark—have often remained obscure to botanists and other scientists.
A new three-dimensional imaging technique now has shed (laser) light on how plant cells begin forming these new features. Described in a study led by Romain Fernandez, of Equipe-projet Virtual Plants, Institut National de la Recherche en Informatique et en Automatique at Sophia Antipolis in France, the results were published online June 13 in the journal Nature Methods (Scientific American is part of Nature Publishing Group).
Unlike the typical case with many animals, plants do not start out with miniature structures that will form more fully later, such as a human fetus' arm buds that appear soon after egg fertilization. Most plants first arise from a seed or bulb as a simple stalk, going through morphogenesis as they mature.
To peer into the microscopic processes, the researchers stained meristem cells, which are plant pluripotent cells responsible for development of key organs (such as flowers and roots), in the well-studied flowering Arabidopsis thaliana as well as in rice roots. The team then trained confocal laser-scanning microscopes on the growing plants from multiple angles. This digital information was then run through novel computer algorithms to reassemble the structures—cell-by-cell—in three dimensions, enabling the creation of video (see below) animating the cells' structural changes.
In Arabidopsis, the flower meristem cells divided about every 19 to 24 hours and multiplied to "several hundred cells, even before the onset of differentiation and organ formation," the authors noted. "We can now address a long-standing question on the precise nature of cell division rules in growing tissues and organs," Fernandez and colleagues noted in their study.
The technique and reassembly algorithms could also be useful for other plants and should be able to also track cell death, the researchers noted. They might even be adaptable to observe "cell movement and/or cell death in animal tissues." But in the meantime it can be put to work validating long lists of hypotheses about plant growth—and condensing days of grass growing into short, relatively action-packed films.
