A closer look at Fasciated Haworthia

Today, we’ll be taking a closer look at a fasciated Haworthia succulent, also known as the “zebra succulent”. This imaging adventure was undertaken as a part of our Diagnostic Devices and Imaging lab course.

This is the plant we will be imaging:

The Haworthia succulent is akin to aloe vera. It has a similar spine-like structure, which is filled with a jelly-like substance. To image this plant, the following materials were used:

A glass slide was used to mount the leaf specimen (shown to the left of the glass slide). Scissors were used to cut a cross-section of the leaf. A phone flashlight was used to illuminate the image.

The leaf, shown in the image above, was prepared on a glass slide. The glass slide was then loaded into the foldscope for imaging. Adhesive stickers, provided with the foldscope kit, were used to mount the sample onto the glass slide. Scissors were used to cut a cross-section of the leaf.

This is a leaf cross-section mounted on the glass slide. There is a small, fibrous extension protruding from the bottom of the slice. We will be examining this fibrous filament further.

To begin, the glass slide was lightly pressed against the foldscope lens to decrease distance between the specimen and the lens. This strategy facilitated focusing on the image. A magnetic cellphone camera mount was used to easily couple a phone camera and the foldscope lens. Images were obtained using a Samsung Galaxy S21 Ultra phone.

We can see some clumps of cells here. The structure appears slightly gelatinous, suggesting that these may be cells trapped in the jelly-like substance found in the center of the leaf’s cross-section.

With strategic positioning, we can begin to see the interface between the chloroplast-abundant leaf layer and the gelatinous substance that fills the leaf (similar to aloe jelly). The image below clearly shows the interface of the leaf encasing and the interior jelly substance.

You can clearly see the interface between globular leaf cell clusters containing chlorophyll (green region) and the gelatinous layer inside the leaf (clear region). Some bubbles are visible in the gelatinous layer.
In this image, the large bubbles in the gelatinous layer are far more visible. These are likely pockets of air trapped in the jelly.

In an attempt to view cells in the plant, a pseudo- phase contrast approach was adopted. Rather than shining the light directly on the specimen, the specimen was slightly tilted away from the light to cast slight shadows and increase contrast of small structures in the sample. Using this strategy, plant cells became visible as seen below.

Hexagonal cell structures are visible in this image. You can appreciate that some cells have a more intense green pigment, suggesting that these cells are producing more chlorophyll.
This image shows a closer look at the highly pigmented cells that are likely producing higher amounts of chlorophyll. The cells are organized in a very precise, spatial pattern, likely to maximize their surface area.

In these images, one can appreciate that although the cell layer and gelatinous substance layer are separated, bubbles can be seen throughout the cross-section. This is likely to facilitate water and nutrient transport in the succulent since such plants are expected to survive extended periods of time without water.

Finally, it was possible to obtain a closer look at the filamentous extension alluded to earlier. Below is a magnified image of the filament:

The filament is highly striated and fibrous. This suggests that these filaments provide structural support and are likely the source of the Haworthia leaves’ rigidity.

Overall, this imaging adventure provided further insight into the Haworthia succulent’s microscopic structure. It was observed that the leaf consisted of an outer plant cell layer, filled with a gelatinous substance. The plant cell layer consisted of highly organized, hexagonal cells, with varying shades of green – indicating varying levels of chlorophyll production. Although the gelatinous layer was largely separated from the plant layer, some gel bubbles/pockets, were visible in the plant cell layer. Finally, fibrous filaments run through the plant cell layer to provide structural support and rigidity.