High energy x-rays are shedding light on plants with possible implications for heavy metal decontamination, say Japanese scientists. The team has used the tightly focussed rays to image the cadmium distribution in a type of thale cress, Arabidopsis halleri. 

X-ray spectroscopy reveals that Arabidopsis halleri accumulates cadmium in its hairs

Certain Arabidopsis species have received much attention in recent years because of their ability to accumulate heavy metals from the ground. This has applications in phytoremediation, in which such plants are sown on contaminated sites, harvested, and the toxic metals then disposed of safely.

But developing these applications requires an understanding of how the metals accumulate in these plants, which so far has proved challenging. For scientists studying plant metal distributions, the method of choice is x-ray spectroscopy. Yet their studies have been limited by the availability of only low-energy x-rays, which are absorbed by air, making samples difficult to examine. Izumi Nakai and colleagues at Tokyo University of Science have now shown how the optics can be adjusted to produce high-energy x-rays.

This advance allows the plant samples to be analysed in air, says Nakai. Not only that, but the x-rays can be focussed onto a micrometre-sized area. This meant that the team could determine the cadmium distribution at the subcellular level.

The researchers discovered that the cadmium lies in rings around the bases of tiny hairs on the plant, and is found together with zinc. Future work, says Nakai, will focus on investigating the change in cadmium distribution over time and the chemical form of cadmium in the plant. This, he says, should contribute to the development of practical phytoremediation technologies.

David Koppenaal from Pacific Northwest National Laboratory, Richland, US, says 'metal localisation in cells is an important yet vexing analytical problem, since metals can occur naturally in cells at concentrations that vary by 10 orders of magnitude. This study and others like it are opening the doors to better understanding of metal incorporation and export in cells.'

David Barden