Pushing and Pulling in Plants

By Fenella Saunders

Stems use mechanical forces to control growth between their layers of tissues.

Biology Physics Technology Botany Morphology

This Article From Issue

September-October 2023

Volume 111, Number 5

Page 272

DOI: 10.1511/2023.111.5.272

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Relatively few organisms are a single cell thick, so their layers of cells have to work together to build a functional structure. Genes in different tissue layers are known to influence one another’s activity, and most of the time, that communication is assumed to occur via chemical signaling. But because the layers are in contact, there’s another option: mechanical forces. “We think of a biochemical signal as the analogy of verbal communication: You want to get somebody to do something, you tell them to do it. But tissue layers interacting with each other via pure mechanics is like me grabbing somebody and moving them to where I want to do something,” says Robert Kelly-Bellow, a plant biologist at the John Innes Centre in the United Kingdom.

The tiny water plant Utricularia gibba usually has a straight central vasculature surrounded by blades and an epidermis (*shown in an idealized simulation as yellow, cyan, and purple at A–C and E–F above*). But when the plant is mutated into a dwarf with a thick epidermis, its vasculature becomes twisted (*confocal microscope image at left*). In a simulation, the normal growth rate (*shown in red at D; growth scale at Q*) in the dwarf plant drops to zero just for its epidermis (*white, G*), and the stem’s internal structure—growing normally—begins to buckle under the constriction (H). This twisting growth puts the epidermis in tension (I) but relieves some of the internal compression (*shown at J, stress scale for tension [t] and compression [c] at R*). The resultant growth rate is low for the epidermis (K) and variable inside (L), resulting in the warped vasculature (*shown at M–P*). The simulation demonstrated that mechanical forces could explain these tissue interactions. See a video of the simulation process below.

**Images from R. Kelly-Bellow et al., 2023, *Science* 380:1275; simulation by Richard Kennaway**

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