Cryo-FIB SEM imaging of plant matter

Equipment case study - Cryo-FIB SEM

ECFP has access to the cryo-FIB SEM facility located within the School of Physics & Astronomy at the University of Edinburgh. It provides a powerful three-in-one imaging facility for opaque soft matter. The instrument’s cryo mode gives the option of imaging a wide range of materials including liquids, gels, polymers, and biological matter. Samples up to a few micrometres thick can be frozen in milliseconds – this prevents the formation of ice crystals and allows samples to be imaged as close to their natural state as possible.

The benefits of this approach can be illustrated using a leaf sample. Without freezing, the instrument’s high vacuum would boil the water within its structure, drying it out and leaving a structure different to what would be found in nature (compare a grape and a raisin). Looking at the leaf in its frozen, hydrated state allows researchers to study its structure close to how it would be in its natural environment, and at resolutions much better than optical microscopy.

A freeze-fractured cryo-SEM image of a common privet leaf (Ligustrum vulgare) epidermis is shown above. It is possible to discern the distinct sections that make up the leaf structure. The microscope has resolution down to ~1nm, enabling it to capture the individual chloroplasts that produce the leaf’s energy through photosynthesis (image below). At the top of this image, the surface ornamentation of the leaf can also be seen.

Another cross section of the leaf contains 1-2 layers of collenchyma cells (ones with thick primary walls). Below the epidermis, some hairs can be seen.

Examining the “midvein” that runs down the centre of the leaf reveals a vascular bundle that makes up part of the leaf’s transport system moving water and nutrients throughout its structure.

These vasuclar bundles contain xylem cells, which develop secondary wall thickening over time as seen in the image below.

Finally, another image of the plant’s midvein contains a variety of lignified (“woody”) and unlignified cells.

We thank Dr Rafael da Silva Cruz (School of Biological Sciences) for his insightful comments on the images shown here. The cryo-FIB SEM facility is available to all researchers across the university, researchers from other academic institutions and external users including industry. Interested in exploring potential applications further? Please contact us to discuss how we can help.

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Cryo-FIB SEM imaging of plant matter

Equipment case study - Cryo-FIB SEM

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