Here’s what a leaf looks like during a fatal attack of bubbles

Simple equipment triumphs in revealing how bubbles kill plant leaves during drought

lab images of embolisms in leaf veins

DEATH BY BUBBLE Mundane tools beat fancy X-ray setups in tracking how invading air bubbles kill leaves during drought, as seen in (clockwise from top) a Pteris fern, oak leaf and Adiantum fern.

T.J. Brodribb et al/PNAS 2016

A decent office scanner has beaten X-ray blasts from multimillion-dollar synchrotron setups in revealing how air bubbles kill plant leaves during drought.

Intricate fans and meshes of plant veins carrying water are “among the most important networks in biology,” says Timothy Brodribb of the University of Tasmania in Hobart, Australia. When drought weakens the water tension in veins, air from plant tissues bubbles in, killing leaves much as bubble embolisms and clots in blood vessels can kill human tissue. As climate change and population growth increase risks of water shortage, Brodribb and other researchers are delving into the details of what makes some plants more resistant than others to drought.

The high energy of X-rays destroys delicate leaf tissue. So, based on a chat with microfluidics specialist Philippe Marmottant of the French National Center for Scientific Research, Brodribb tried repeatedly scanning a leaf with a light source below it to reveal darkening lines as air bubbles shot through the veins. A microscope or scanner proved perfect. Tracked this way, an invasion of killer bubbles “looks like a lightning storm,” he says.

He was surprised to see that bigger veins, despite their robust looks, fail before tiny ones (blue indicates earliest failures; red, the latest), as seen in an oak leaf (lower right) and Pteris fern (top). And networks in ferns with simpler branching patterns, as in the Adiantum ferns at bottom left, crash quickly.

This system of visualizing plant plumbing gave better resolution than expensive and elaborate X-ray techniques had, Brodribb, Marmottant and Diane Bienaimé report online April 11 in the Proceedings of the National Academy of Sciences

DEATH BY BUBBLE By imaging a maidenhair fern leaflet (left panel) at 30-second intervals, researchers could subtract the difference between the images (center panel) to see where an embolism formed. Images were colorized (right panel) by how much time had elapsed and then combined, as shown in the second clip, to give a complete picture of the leaf’s response to water stress. T.J. Brodribb et al/PNAS 2016

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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