Behind the Cover: New Phytologist 218:2: April 2018

Hyperaccumulator plants have the unusual ability to accumulate extreme concentrations of metal(loid)s in their living tissues. In the Tansley review behind the latest cover of New PhytologistAntony van der Ent and colleagues discuss the different techniques, based on X-rays, used for probing the internal distribution and chemical form of different elements in plants.

The cover shows images of various hyperaccumulator plants, captured using a technique called X-ray Fluorescence Microscopy. Each element is depicted in a different colour, making up a red-green-blue (RGB) image.

Image: X-ray Fluorescence (XRF) elemental maps of hyperaccumulator plants. The tricolour composite images show (clockwise from top left): a young plant of Berkheya coddii (red, potassium; green, calcium; blue, nickel), seed capsules of Alyssum murale (red, potassium; green, calcium; blue, nickel), seed of Berkheya coddii (red, potassium; green, calcium; blue, nickel), root cross-section of Senecio coronatus (red, iron; green, nickel; blue, potassium), and seedlings of Alyssum murale (red, calcium; green, nickel; blue, Compton scatter).
X-ray Fluorescence (XRF) elemental maps of hyperaccumulator plants. The tricolour composite images show (clockwise from top left): a young plant of Berkheya coddii (red, potassium; green, calcium; blue, nickel), seed capsules of Alyssum murale (red, potassium; green, calcium; blue, nickel), seed of Berkheya coddii (red, potassium; green, calcium; blue, nickel), root cross-section of Senecio coronatus (red, iron; green, nickel; blue, potassium), and seedlings of Alyssum murale (red, calcium; green, nickel; blue, Compton scatter).

The top left of the cover shows a young seedling of the nickel hyperaccumulator plant Berkheya coddii from South Africa. Potassium shows up as red, calcium as green, and nickel as blue. Other panels show seed capsules and seedlings of the nickel hyperaccumulator Alyssum murale from Albania. Finally, a root cross-section of another South African nickel hyperaccumulator plant species (Senecio coronatus) from the Sunflower-family (Asteraceae).

Antony and colleagues captured the images at the Australian Synchrotron in Melbourne. X-ray Fluorescence Microscopy uses a synchrotron (a very large electron accelerator) to generate a focussed beam of X-rays that is pointed at a sample. Moving the sample through the beam generates ‘fluorescent X-rays’, which are captured by a detector. Different elements in different concentrations produce characteristic X-rays, which are then used to build an ‘elemental map’ of the sample. This is what the cover image shows.

Elemental mapping with Maia

“Unique about this work is that we used a revolutionary X-ray detector called Maia (a massive array of 384 tiny detectors),” said Antony Van der Ent. “Maia enables extremely fast capture of fluorescent X-rays, and this makes it possible to obtain elemental maps that are many millions of pixels (megapixels) in size in hours. It also makes it possible to obtain elemental maps of highly sensitive samples, as such as living plants, because it is so fast (hence minimising the radiation dose which can be damaging to living cells).”

Antony aims to better understand how hyperaccumulator plants take up and store metals such as nickel, cobalt and zinc. “This information can be used to infer the ecophysiology of these plants, and the evolution of metal tolerance and hyperaccumulation. Eventually, this knowledge is useful for developing hyperaccumulator plants as ‘metal crops’ in novel phytotechnologies, such as phytomining.”

Read the paper: van der Ent, A., Przybyłowicz, W. J., de Jonge, M. D., et al. (2017) X-ray elemental mapping techniques for elucidating the ecophysiology of hyperaccumulator plantsNew Phytologist. doi: 10.1111/nph.14810


 

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Mike Whitfield (@mgwhitfield)
Development Coordinator
New Phytologist