Plants need carbon dioxide to flourish, but during a drought, gases can leak inside the veins that supply water, cutting off the flow of fluid and killing the plant. In fact, these blockages are the leading cause of death for thirsty plants. But until now, no one has been able to see how the lethal air pockets develop. To watch this process unfold in leaves, researchers took advantage of their natural transparency, using light microscopes to chart the origin and spread of bubbles in several species, including the maidenhair fern (the first leaf in the video, above) and the oak tree (the final leaf). The blockages, the team reports today in the Proceedings of the National Academy of Sciences, first crop up in the largest veins. Water circulation slows as existing bubbles spread and new ones start to form, eventually killing the leaf. But not all leaves are equally doomed—some have developed “short cut” veins that, like back roads connecting bigger highways, provide additional outlets for the water. Whereas a few air pockets quickly shut down water flow in simple ferns, plants with more complicated networks of criss-crossing conduits, such as oak and eucalyptus, decline more slowly. Indeed, scientists suspect flowering plants evolved these interconnected plumbing systems in part to protect against the dangers of dry spells.
(Video credit: Science/AAAS)