As any diver will tell you, air embolisms (when a bubble of gas blocks the flow in a vital artery) are bad news. Plants can suffer from them too, particularly during drought, but we still have much to learn about how vulnerable the xylem in different parts of a plant are to embolism, or how they might spread when they do happen.
In the research behind this issue’s cover image, Rob Skelton and colleagues used X-ray micro-computed tomography (microCT) scans to follow the spread of embolism through the internal plumbing of plants as they became more water stressed. To find out how air enters and spreads through a plant’s plumbing, Rob Skelton and colleagues placed dehydrating tomato plants in front of X-ray beams generated by the particle accelerator at the Australian Synchrotron, in Melbourne.
The resulting scans generated many 2D images or slices showing cross-sections of the dehydrating plants (about 2,000 per about 1 cm of plant tissue), which were then stacked on top of each other to ultimately produce a 3D image of the entire scanned section of the plant. Generating the final 3D images requires some fairly advanced software and a lot of patience (not to mention computer processing power).
The image on the cover is a 3D reconstruction of a tomato plant root that is suffering from severe water stress. The red dots in the cross section at the top show xylem – normally filled with water – that have become filled with air. Once filled with air, the xylem can no longer transport water and nutrients to the different parts of the plant that require these resources, and the plant suffers as a result.
By tracing the amount of air in different parts of the tomato plant, Rob Skelton and colleagues show that the roots, stems and leaves all begin to suffer embolisms at the same level of water stress. Researchers previously thought that less ‘valuable’ parts of the plant, like the leaves, would begin to fail first, but this doesn’t seem to be the case: different tissues within the plant are equally susceptible to water stress. “By establishing these critical points of failure in the plant as they become more and more stressed we are able to make better predictions about the kind of stresses that plants can tolerate before they start to lose functionality,” said Rob.
Read the paper: Skelton, R. P., Brodribb, T. J. and Choat, B. (2017) Casting light on xylem vulnerability in an herbaceous species reveals a lack of segmentation. New Phytologist 214: 561–569. doi: 10.1111/nph.14450
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